Agricultural and Food Science, Vol. 18 (2009): 57-75 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 57 © Agricultural and Food Science Manuscript received September 2006 Waste composts as nitrogen fertilizers for forage leys Tiina Tontti*, Arja Nykänen and Miia Kuisma MTT Agrifood Research Finland, Plant Production Research, Lönnrotinkatu 3, FI-50100 Mikkeli, Finland, *email: tiina.tontti@mtt.fi Two field experiments, conventional grass ley and organic grass-clover ley, were established with barley as a nurse crop in spring 2000 and given either low or high fertilization with mineral fertilizer (Mineral) or composts. The compost types were municipal biowaste (Biowaste), biowaste + sewage sludge (BioSludge) and cattle manure (Manure). Plant yields and nitrogen (N) uptakes were measured for three years and ef- ficiency of N utilization was estimated. In single application of compost, the total N was mainly in organic form and less than 10% was in inorganic form. Along with increasing amount of inorganic N applied in compost, the yield, N uptake and N recovery increased during the application year. The highest compost N recovery in the application year was 12%, found with Biowaste. In the following years the highest N recovery was found where the lowest total N had been applied. Clover performance was improved in the organic grass-clover ley established with BioSludge fertilization, producing total ley yield comparable with Manure compost. High total N application in composts caused high N surplus and low N use efficiency over three years. Generally, moderate compost fertilization is suitable for ley crops when supplemented with mineral N fertilizer or clover N fixation. Key-words: compost, biowaste, sewage sludge, yield, N uptake, N recovery, apparent bio-available N, N balance, N use efficiency Introduction High amounts of organic waste are produced in mu- nicipalities. Both from the ecological and economic point of view the valuable resources in organic waste should be recycled in a sustainable way, and composting is an efficient stabilizing method for treating the organic waste materials (Epstein 1997). Although the quality of waste composts has continuously improved and the contents of heavy metals and pathogens are decreasing and restricted, there are still many challenges for utilizing waste composts in agriculture. Such challenges include A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 58 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 59 public acceptance, problems of integration into agricultural practices, quality control, logistics and organization, as well as environmental regulations, economic viability and sustainability (Westerman and Bicudo 2005). The potential beneficial effects of compost ap- plication on fields include increased organic matter, total nitrogen (N) and humus contents of soil. In addition, soil enzyme activities, water-holding ca- pacity, soil structure and plant nutrient supply may be improved by compost applications (Jakobsen 1995, Debosz et al. 2002, Hartl and Erhart 2005). Waste composts include significant amounts of nu- trients and the amount of total N in composts pro- duced from source-separated municipal biowaste can be up to 20 g kg-1 on dry weight basis (Houot et al. 2002, Erhart et al. 2005). Comparable Finn- ish biowaste composts which were matured over 6 months have been found to include 9–20 g total N kg-1 in dry matter and 2.6–4.1 g total P kg-1 in dry matter (Hänninen and Mäkelä-Kurtto 1995). It has been estimated that the nutrients returned to agricultural soil in organic waste could replace about 17% of the nutrients annually applied to soil with inorganic fertilizers in Finnish food produc- tion (Antikainen et al. 2005). The plant availability of N from waste composts is generally low since the majority of total N is in organic form and the mineralization from compost products is usually slow. Various other factors, too, such as compost quality (influenced by origin and processing of waste), climate, soil properties and management as well as N uptake by the crop, affect the N dynamics in compost-amended soil (Amlin- ger et al. 2003). The mineralization of N is highest during the first year after compost application, but even then the plant N uptake from biowaste com- post is usually below 15% of the total N content in compost. During the subsequent years, approxi- mately 2–8% of the total N in compost is available to plants per year (Gagnon et al. 1997, Smith et al. 1998, Amlinger et al. 2003). However, the Finnish implementation of the EU nitrate directive 91/676/ EEC (Council of State 931/2000) may limit the amounts of N applied to agricultural fields to 170 kg ha-1 total N. If this limit of total N application were considered to cover compost fertilization as such, it might result with less than 30 kg N in crop uptake, with no possibility for mineral N addition during the first year. The agronomic value of waste composts de- pends highly on their ability to increase the crop yields, whereas from the environmental point of view the quality of waste composts should be high enough to avoid potential harmful effects and rather to improve the quality of soil, plants and environ- ment (Stratton et al. 1995, Amlinger at al. 2003). Composting municipal organic waste together with sewage sludge (i.e. biosolids) can be a way of op- timizing the composting process and of improving the product quality, especially by increasing the nu- trient contents in compost (Tognetti et al. 2007). In high-quality composts the contents of harmful ele- ments, such as heavy metals, pathogens and toxic organic compounds, are very low or absent, and the application rates could be determined by match- ing the plant-available N from the waste compost with the N requirements of crop (Mamo et al. 1999, Amlinger et al. 2003). However, this may require high amounts of applied compost and could lead to salt or heavy metal accumulation and thus to reduced soil quality. Therefore, combination of low amendment rates of composts with sufficient min- eral fertilizer has been suggested as an advisable method to meet the crop N requirements (Gagnon et al. 1997, Sullivan et al. 2002). Another approach could be to include legumes in crop rotation and thus to utilize their ability to fix atmospheric N (Lynch et al. 2004). Difficulties in predicting the N supply from composts may limit their routine use in crop pro- duction. A number of methods have been devel- oped for estimating the N availability, but there is no standard method for doing this. Nutrient dynamics in complex soil-plant systems could be formulated with modelling, based on extensive data sets (Gabrielle et al. 2005). More simply, the plant-available N from the applied fertilizer could be calculated based on crop N uptakes with inor- ganic N contents of soil included in the assessment (Iglesias-Jimenez and Alvarez 1993). Alternatively, the utilization of N could be estimated based on crop N uptakes only (Lynch et al. 2004, Hartl and Erhart 2005). In the latter two methods the ferti- A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 58 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 59 lized crop may be compared with the unfertilized crop, but potential losses of N by denitrification, leaching or volatilization and the N remaining in plant roots are usually excluded. In order to achieve a balance between inputs and outputs of nutrients, nutrient budgets have been used as a tool to improve nutrient management over periods longer than one growing period within or- ganic farming systems (Watson et al. 2002). De- termining N use efficiency (NUE) is another way of measuring the utilization of applied N and may be calculated as a ratio between crop N uptake and applied fertilizer N, i.e. the ratio between outputs and inputs in a cropping system (Cassman et al. 2002). The application of waste-based composts has been relatively uncommon in Finland, and research has merely focused on processing waste materi- als, including source-separated biowaste or various sludges from forest industry waste water or sewage water treatment plants (Jokinen 1990, Rantala et al. 1999, Venelampi et al. 2003). In some previ- ous studies, also the quality of composts produced in open-air windrow composting systems has been considered in terms of their final application (Hänninen and Mäkelä-Kurtto 1995, Koivula et al. 2000, Hänninen et al. 2001). The aim of this study was to test waste composts made of municipal biowaste and sewage sludge as fertilizers for ley production in conventional and organic cropping systems. Specifically, the aim was to define the effect of two levels of waste compost on crop yield and N uptake over three subsequent years and to estimate the utilization and efficiency of N by various methods. Material and methods Experiments and fertilizations Two field experiments were established in 2000, a conventionally cultivated grass experiment in Mikkeli (61°40’ N, 27°13’ E) and an organically cultivated grass-clover experiment in Juva (61°53’ N, 27°53’ E). The soil characteristics in Mikkeli were medium fine sand, pHH2O 6.1, organic C 5.6%, total P 1.1 g kg-1 soil, PAAAc-extractable 8.8 mg l -1 soil (class “satisfactory” according to the Finnish soil classification), those in Juva were fine sandy mo- raine, pHH2O 6.6, organic C 3.0%, total P 1.6 g kg -1 soil, PAAAc-extractable 20.4 mg l -1 soil (class “good”). The experimental sites were situated 45 km apart and the climatic data from Mikkeli represent the weather conditions in Juva reasonably well (Table 1). Precipitation was monitored on field in Mikkeli and mean temperatures were obtained from the observation station of the Finnish Meteorological Institute 1 km away from the grass experiment. The grass experiment was sown with timothy (Phleum pratense, L., 10 kg ha-1) and meadow fescue (Festuca pratensis, Huds., 15 kg ha-1) with spring barley (Hordeum vulgare, L., 350 seeds m-2) as nurse crop. The grass-clover experiment Precipitation, mm (1) Mean temperature, °C (2) average 1961–1990 2000 2001 2002 average 1961–1990 2000 2001 2002 May 40 32 47 48 9.4 9.3 8.0 10.8 June 55 75 115 92 14.4 13.8 13.6 15.3 July 68 92 120 79 16.1 16.3 19.0 18.4 August 88 66 39 19 14.1 13.8 14.1 16.6 September 68 22 60 21 8.8 7.6 10.3 8.5 (1)Monitored at the research station. (2)From the Finnish Meteorological Institute. Table 1. Weather conditions in Mikkeli during the experiments and in the reference period 1961–1990. A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 60 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 61 was sown with red clover (Trifolium pratense, L.), timothy and meadow fescue (seed rates 5, 8 and 12 kg ha-1, respectively), with spring barley as nurse crop (350 seeds m-2). In both experiments, barley nurse crop was grown in 2000 and forage ley in 2001 and 2002. The experimental set-up was split-plot design, with two application rates in the main plot (low/ high), fertilizer types in the sub-plot and an un- fertilized control treatment at the main plot level. Four replications for each treatment were used and the plot size was 3 m ×10 m with a 1.5 m × 7 m harvesting and sampling area within the plot. The fertilizer types in the grass experiment were mineral NPK fertilizer (Mineral), municipal source-separated biowaste compost (Biowaste) and co-composted municipal source-separated biow- aste and municipal anaerobically digested sewage sludge (BioSludge). Accordingly, in the grass-clo- ver experiment the fertilizer types were cattle ma- nure compost (Manure), Biowaste and BioSludge. The Manure was produced by a farmer by compost- ing cattle manure with 1/2 of straw by volume. The BioSludge consisted of approximately 1/3 biowaste and 2/3 sludge. The co-operating composting facil- ities applied a static, aerated tunnel technique for Biowaste and BioSludge. The compost producers selected good-quality compost batches of adequate maturity (aimed at over 6 months processing) and sieved the material for the experiments (Table 2). The composts were applied on soil surface in May 2000 and mixed with the upper soil layer (within 0–10 cm) by harrowing immediately. The application rates of compost aimed to satisfy the plant P requirement for two (low application) or four (high application) years, leading to variable N inputs into the soil in 2000 (Table 2). In the conventional grass experiment, the applications of Biowaste were 20 and 40 Mg ha-1 and those of BioSludge were 22 and 44 Mg ha-1 fresh matter for low and high application, respectively. For the Mineral plots, the nutrients were given according to fertilization recommendations (Table 2). In the organic grass-clover experiment, the applications of Manure were 17 and 33 Mg ha-1, those of Biow- aste 23 and 45 Mg ha-1 and of BioSludge 9 and 18 Mg ha-1 for low and high application, respectively. For the conventional grass ley in 2001 and 2002, mineral N (250 kg ha -1 year-1) and K (130–160 kg ha-1 year-1) were supplied for all the treated plots (excluding the unfertilized control), aiming to de- scribe the fertilization practice of a conventional farm. In the organic experiment, no external fertili- zation was applied after compost application, apart from the input of N fixation by red clover. Sampling and analyses Compost samples were taken just before the ap- plication, with 10 sub-samples collected and mixed thoroughly. Final samples of 1 litre were taken from these and stored frozen. Crop yields were measured from the 10.5 m2 area at harvesting and plant samples were collected for further analysis; total yield of barley grain and a minimum of 1 kg of barley straw and leys. Due to weak establishment of the barley nurse crop in the conventional experiment, the plant growth was harvested as a whole crop silage in late July. After that the grass was cut once in late September 2000. Both fractions were combined in the total yield of the conventional experiment in 2000. In the organic experiment the cereal nurse crop was threshed at the end of August 2000. During the subsequent two years the conventional grass ley was cut three times and the organic grass-clover ley twice a year at silage stage. The plant samples from the organic ley were sorted to separate grasses and clover and weighed for determination of clover content of the yield. The plant samples were dried at 60 °C, weighed for dry matter and ground for the analysis of total N. Soil samples were taken before the establish- ment of the experiments and thereafter every au- tumn (September) and spring (May). Composite soil samples were collected with a soil drill from the plough layer (approximately 0–20 cm deep) of 10–15 systematically chosen points and mixed. A final sample of 0.75 dm3 was taken from the mix- ture and stored frozen. Ammonium (NH4 + -N) and nitrate (NO3 - -N) contents of the composts and soil were determined A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 60 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 61 C on ve nt io na l g ra ss e xp er im en t O rg an ic g ra ss -c lo ve r e xp er im en t C ha ra ct er is tic s of c om po st s C ha ra ct er is tic s of c om po st s To ta l P A va ila bl e P To ta l N In or ga ni c N O rg an ic C N H 4/ N O 3 To ta l P A va ila bl e P To ta l N In or ga ni c N O rg an ic C N H 4/ N O 3 g kg -1 d ry m at te r C /N pH g kg -1 d ry m at te r C /N pH M an ur e 6. 9 4. 4 26 0. 7 42 5 16 .3 n. d. 35 B io w as te 6. 9 1. 7 27 2. 1 28 8 10 .7 6. 8 6. 7 B io w as te 5. 2 2. 5 25 2. 2 31 5 12 .6 6. 9 6. 8 B io Sl ud ge 14 .2 0. 5 22 1. 1 31 1 14 .1 6. 4 0. 7 B io Sl ud ge 12 .2 0. 4 24 1. 8 30 4 12 .7 6. 4 0. 6 N ut ri en ts a pp lie d N ut ri en ts a pp lie d P (k g ha -1 ) N (k g ha -1 ) P (k g ha -1 ) N (k g ha -1 ) To ta l A va ila bl e % To ta l In or ga ni c % To ta l A va ila bl e % To ta l In or ga ni c % M in er al lo w 68 64 94 60 60 10 0 M an ur e lo w 91 62 68 36 7 10 3 B io w as te lo w 68 18 26 27 7 22 8 B io w as te lo w 51 26 51 25 7 23 9 B io Sl ud ge lo w 24 8 10 4 41 3 20 5 B io Sl ud ge lo w 60 2 3 12 6 9 7 M in er al hi gh 13 5 12 7 94 60 60 10 0 M an ur e hi gh 17 8 12 1 68 72 0 20 3 B io w as te hi gh 13 4 36 27 54 4 44 8 B io w as te hi gh 10 0 52 52 50 3 44 9 B io Sl ud ge hi gh 49 3 20 4 82 0 39 5 B io Sl ud ge hi gh 11 7 4 3 24 8 18 7 To ta l P = fr om w et c om bu st io n w ith IC P- A E S, A va ila bl e P = A A A c ex tr ac tio n, T ot al N a nd O rg an ic C fr om d ry c om bu st io n (L ec o) , p H e xt ra ct io n 1: 2. 5 w ith w at er In or ga ni c N = s um o f a m m on iu m (N H 4+ )- N a nd n itr at e (N O 3- )- N (f ro m K C l e xt ra ct io n) , N H 4/N O 3 = ra tio o f a m m on iu m -N a nd n itr at e- N , n .d .= no t d et er m in ed Ta bl e 2. C ha ra ct er is tic s of c om po st s at th e tim e of a pp lic at io n in s pr in g 20 00 a nd a m ou nt s of P a nd N a pp lie d in c om po st s an d fe rt ili ze d co nt ro l i n 20 00 a nd p er ce nt - ag e (% ) o f s ol ub le fr om th e to ta l a m ou nt . A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 62 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 63 from thawed samples extracted with 2 M KCl (ex- traction ratio 1:2.5 by volume) and analyzed spec- trophotometrically (Mulvaney 1996). The compost samples were air-dried and ground to pass a 2-mm sieve and analyzed for total N and C content by the dry combustion method (Leco CN-2000 analyzer). For total P content in the composts, wet combus- tion (nitric acid) and determination with ICP-AES were applied (Agricultural Research Centre of Finland 1986). The soluble P in composts was ex- tracted with acidic ammonium acetate (extraction ratio 1:10 by volume, pH 4.65) and determined photometrically by the molybdenum blue method (Agricultural Research Centre of Finland 1986). The N content of plant samples was analyzed by using the dry combustion method (Leco CN-2000 analyzer). Calculations and definitions The N uptake was calculated as a product of dry matter (DM) yield of harvested plants and N con- centration of the plant sample, while the amount of N in roots and stubble was not included. For the organic experiment, the N uptake of grass and clover were calculated separately. The utilization of fertilizer N was described by estimating the additional N uptake (ANU) on annu- al basis by subtracting the N uptake in unfertilized crop from the N uptake in fertilized crop. For the first year, the estimated ANU from fertilizer was assumed to consist of two components, the amount of inorganic N applied in spring in compost and the rest of ANU representing an estimate of N released from organic matter (OM) in soil (ANUOM) during the growing period. Thus, the ANUOM in soil was estimated by subtracting the amount of inorganic N in applied compost (see Table 2) from the total ANU. Due to a single compost application, the ANUOM was calculated only for the first year. The efficiency of fertilizer N utilization was estimated with two equations, N recovery and apparent bioavailable N (ABN). The N recovery describes the proportion of fertilizer N utilized by plants (i.e. ANU) to the applied amount of fertilizer N. The N recovery was calculated annually accord- ing to Eq. (1) (Iglesias-Jimenez and Alvarez 1993, Hartl and Erhart 2005): Eq. (1) N recovery % = (( NUp – NUc ) / Nf ) × 100 where NUp is the total plant N uptake, NUc is the N uptake by the unfertilized control and Nf is the total N applied in fertilizer. The ABN describes the amount of fertilizer N utilized by plants and available inorganic N in soil in relation to the applied N amount. ABN was estimated annually according to Eq. (2) (Iglesias- Jimenez and Alvarez 1993): Eq. (2) ABN % = ((NUp + NSs – NUc – NSc ) / Nf ) × 100 where NUp is the total plant N uptake, NSs is the inorganic N in soil as determined from the plough layer in autumn, NUc is the N uptake in the unfer- tilized control, assumed to be equivalent to the N uptake derived from soil reserve, NSc is the inor- ganic N in the control plot as determined from the plough layer, assumed to be equivalent to inorganic N derived from the soil reserve, and Nf is the total N applied in the fertilizer. In the estimates of N utilization and efficiency, N uptakes from all the cuts of the growing period were summarized. When estimating ABN, the con- centrations of inorganic N in soil were calculated as a sum of NH4 + -N and NO3 - -N in the soil plough layer in autumn. In the N efficiency estimates for the second and third year it was assumed that total N previously added in fertilizer and unused by the previous crops was available for plants in soil dur- ing the following year. Thus, for the second and third year the annual amount of N supply (Nf) was considered to consist of two components: 1) annu- ally added external N (Nf-Annual) and 2) previously added total N that was not found in the uptake of the previous crop (Nf-Remains). In order to estimate atmospheric N input to the grass-clover ley in 2001 and 2002, the biological N2 fixation (BNF) was estimated by Eq. (3), based on a practical model of BNF estimation developed for farm application (Väisänen 2000, Väisänen et al. 2000): A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 62 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 63 Eq. (3) BNF (kg ha-1) = (clover N (%) × clover yield (kg DM ha-1) ) – (0.268 × soil NO3- -Nspring content (kgN ha -1) ) According to these calculations the estimated BNF was equal to the corresponding clover N up- take, because soil NO3 - -N was very low and the effect on BNF estimate was negligible in this ex- periment. In the grass-clover ley during the second and third year, the N uptakes consisted of grass N up- take and clover N uptake, while the annually added external N (Nf-Annual) consisted of “fertilized BNF – unfertilized BNF”. Thus, we could formulate Eq. (1) for the grass-clover ley (GC) as: Eq. (4) N recovery % GC = Because the BNF estimated in the grass-clover ley was equal to the corresponding clover N uptake during the second and third year, factors NUp-Clover, BNFfertilized, NUc-Clover and BNFunfertilized could be reduced from the equation and the N recovery in grass of the grass-clover ley was estimated as: Eq.(5) N recovery % GC-g = Corresponding development and reductions could be made for the basic equation of ABN (Eq. 2), resulting with an estimate of ABN in grass of the grass-clover ley as: Eq. (6) ABN % GC-g = NU p-Grass + NSs – NUc-Grass – NS c × 100 N f-Remains (NUp-Grass + NUp-Clover ) – ( NUc-Grass + NUc-Clover ) × 100 Nf-Remains + BNFfertilized – BNFunfertilized (NU p-Grass – NUc-Grass ) × 100 Nf-Remains The N balance was calculated for the total three-year period in both experiments as a dif- ference between total N input and total N output. The N input consisted of total N added in fertilizer and of estimated N fixation of clover, while output equalled the N uptake in the harvested crop. The N use efficiency (NUE) was calculated as a percent- age of the ratio between total N output and N input over a three-year period (Watson et al. 2002). Statistical analyses The experimental design was a split-plot design where the main-plot treatments (application rate) were in a randomized complete-block design and the sub-plot treatments (compost type) were rand- omized within each main plot. Consequently, the statistical analyses of the annual data were based on the common mixed model for a split-plot design which included three fixed effects (application rate, compost type and their interaction) and three random effects (block, main-plot error and sub-plot error) (Littell et al. 2006). The analyses were performed using the SAS system for Windows, version 9.1.3 and the SAS Enterprise Guide, version 4.1 (SAS Institute Inc., Cary, NC, USA). Pairwise com- parisons were made using two-sided t-type tests. Model assumptions were checked by graphs of residuals. REML was used as an estimation method and degrees of freedom were calculated using the containment method or the Kenward-Roger method (Kenward and Roger 1997). In order to minimize the number of plots, the unfertilized control was randomized only at the main-plot level. Thus the unfertilized control was not included in statistical analyses made according to the split-plot design, and deviations from the unfertilized control were considered visually. In the paired comparisons, only differences within the application rate were considered interesting and compared with each other. This constraint in the number of comparisons helped to minimize type I errors. A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 64 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 65 Results Crop yield and N uptake In the first year of the conventional grass experiment, low compost fertilizations produced about 1000 kg ha-1 lower dry matter yields than the Minerallow which produced 6600 kg ha-1 of barley-grass, and plant N uptakes complied closely with the yield results (Fig. 1). With Minerallow the N uptake was 141 kg N ha-1, while with Biowastelow and BioSludgelow the N uptake was 21 or 29 kg lower, respectively. Com- pared with the unfertilized control in the first year, the dry matter yield was 30–35% higher with low compost fertilization and 47–51% higher with high compost fertilization. Accordingly, compared with the unfertilized control, the N uptake was 28–37% higher with low compost fertilization and 50–58% higher with high compost fertilization. During the second and third year the dry matter yield of grass ley was generally equal for all fertilized treatments, approximately 12000 kg ha-1, since equal mineral N fertilization of 250 kg N ha-1 was applied dur- ing these years. However, in the third year, both yield and N uptake were higher with BioSludgehigh compared with Mineralhigh (Fig. 1). No significant differences could be found in the yield or N uptake between high and low fertilization levels in any of these years. The total biomass and N uptake in the organic spring barley nurse crop was higher with Biow- aste than with BioSludge and Manure composts (p<0.01). The average biomass with Biowaste, Bi- oSludge and Manure fertilization was 4150, 3560 and 3480 kg DM ha-1 and the average N uptake was 69, 53 and 60 kg N ha-1, respectively. The total biomass of unfertilized barley nurse crop was 2620 kg DM ha-1 and the N uptake was 44 kg N ha-1. The grain yield of the organic barley nurse crop fertilized with Biowaste was higher (p<0.05) than with Manure or with BioSludge compost (average 2670, 2350 and 2170 kg DM ha-1, respectively). However, the N uptake of barley grain fertilized with Biowaste was no different from that with Manure compost (Fig. 2), whereas the N uptake with BioSludge was lower than that with Biowaste (p=0.003), with average N uptakes of 56, 50 and 43 kg N ha-1, respectively. The grain yield of unferti- lized barley nurse crop was 1630 kg DM ha-1 and N uptake was 32 kg N ha-1. 0 2000 4000 6000 8000 10000 12000 14000 2000 2001 2002 Cereal-Grass Grass Grass Yield, kg DM ha-1 Mineral Biowaste BioSludge 0-ctrl a b b B A Low High Low HighLow High 0 50 100 150 200 250 300 2000 2001 2002 Cereal-Grass Grass Grass N uptake, kg N ha-1 a b b Low High Low High Low High B B A, ,, , Fig. 1. Total dry matter yield and plant N uptake in the conventional grass ley experiment. Vertical lines indicate stand- ard deviations of measurement replicates. Means denoted by different letters differ significantly from each other with- in the low (a/b) or high application (A/B) with p<0.05. When denoted by ‘, the difference is marginally significant at 0.05 Biowaste (71%) > BioSludge (59%), in the organic grass-clover in Conventional grass (1) Organic grass–clover (2) 2000 2001 2002 2000 2001 2002 ±SD ±SD ±SD ±SD ±SD ±SD Mineral low 89 a 83 75 a 9 47 a 9 Manure low 4 2 3 a 7 7 4 Biowaste low 12 b 9 42 b 8 28 b 14 Biowaste low 8 4 –1 7 5 5 BioSludge low 6 b 9 31 c 5 21 b 7 BioSludge low 6 9 –7 b 10 8 17 Mineral high 58 A 41 69 A 5 38 A 15 Manure high 2 1 4 A‘ 2 3 1 Biowaste high 9 B‘ 7 27 B 3 17 B 5 Biowaste high 6 2 0 4 0 4 BioSludge high 5 B 4 21 C 3 16 B 5 BioSludge high 4 5 –2 B‘ 9 2 8 The N recovery estimate = (fertilized N uptake – unfertilized N uptake) / external N added and remaining in soil (1) Total biomass of barley–grass in 2000 and grass ley in 2001 and 2002. (2) Barley nurse crop (grain + straw) in 2000 and grass fraction of grass-clover ley in 2001 and 2002. Table 4. Efficiency of applied fertilizer N estimated with N recovery (%) in conventional grass and organic grass-clover ley. Means denoted by different letters differ significantly from each other within the low (a/b) or high application (A/B) with p<0.05, or marginally significantly with 0.05 Biowaste (71%) > Manure (60%). In both experiments the low ferti- lization level resulted in better NUE than the high fertilization level (p<0.05). Discussion Yield and N uptake The differences in plant N uptake followed the changes in plant dry matter yield in both experi- ments, which was observed also in other compost fertilization studies (Gagnon et al. 1997, Lynch et al. 2004). In the first year of the conventional grass experiment, both yield and N uptake were lower with low compost fertilizations compared with Mineral fertilization, whereas with high compost fertiliza- tions yield and N uptake did not differ from Mineral. In the organic barley nurse crop, Biowaste produced higher biomass and N uptake than BioSludge or Manure. According to Svensson et al. (2004) the inorganic N amount in compost is probably the most important explaining factor for the yield and N uptake during the application year. In our experi- ments, less than 10% of total N in composts was in inorganic form at the time of application. In the organic experiment the high amount of inorganic N applied in Biowaste, 45 kg ha-1 and twice the amount applied in BioSludge and Manure, explained the differences in crop production. Furthermore, equal amounts of inorganic N applied in Biowaste and Fig. 3. The N balance and N use efficiency (NUE) over a three-year period in the conventional and organic experiment. Estimates were calculated as “N balance = N input – N output” and “NUE% = (N output / N input) × 100”. Means de- noted by different letters differ significantly from each other within the low (a/b/c) or high (A/B/C) application, with p<0.05. (0-ctrl = unfertilized control) 70 C 308 B 489 A 61 b 147 a 647 A 304 a 411 B 143 b -168-51 c-82 c -40 C -251 -400 -200 0 200 400 600 800 N balance, kg N ha -1 CONVENTIONAL ORGANIC 86 A 54 B46 C 87 b 74 c 51 B 61 B 107 A 67 c 113 a115 a 82 b 0 30 60 90 120 150 M in er al B io w as te B io S lu dg e M in er al B io w as te B io S lu dg e M an ur e B io w as te B io S lu dg e M an ur e B io w as te B io S lu dg e Low High 0-ctrl Low High 0-ctrl N use efficiency, % A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 70 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 71 BioSludge in the conventional experiment produced equal yields between compost types. All fertilizations increased yields and N uptakes compared with the unfertilized control during the first year after application, which was found also when Zheljazkov et al. (2006) fertilized the mix- ture of timothy and red clover with municipal solid waste compost. Erhart et al. (2005) fertilized winter cereals with biowaste compost and found annual yield increases of less than 30% compared with the unfertilized control which was mostly lower than the increases of 26–63% we found. The higher amount of inorganic N in compost may partly ex- plain our higher increases, and some could be due to applying composts in spring, higher maturity and total N concentration of compost, or due to moist weather conditions during summer. These experimental soils were rather fertile with favourable capillary water conditions and the weather conditions during mid-summer were moist with average temperatures, whereas the benefits of compost additions might have become more evident in less favourable growth conditions. Additionally, the variable results of compost fertilization and ef- ficiency of N utilization between different studies may be caused by different calculation procedures or experimental plants, source of N addition or fer- tilization level. The maturity of compost and timing of application may also affect the N efficiency but apart from that part of N could be lost and other nutrients than N may affect the crop growth (Fauci and Dick 1994, Sikora and Enkiri 1999, Keeling et al. 2003, Svensson et al. 2004). In a review of several compost fertilization stud- ies Amlinger et al. (2003) concluded that in general 2–8% of the total N in compost remaining in soil after the first year could be used by plants annually in subsequent years. We found the annual N utiliza- tion based on crop production difficult to measure after the application year due to the influence of red clover in the organic system and the mineral N added in the conventional system. Mineral N fertilizer was applied according to annual fertili- zation recommendations for the grass ley in 2001 and 2002 in Finland. The amount was apparently too high when combined with preceding compost additions, since crop production was equal with both fertilization levels. Apparently the added min- eral N fulfilled most of the crop N requirements, whereas compost N was not required. A clear dif- ference between the yields with BioSludgehigh and Mineralhigh was found only in 2002, which could be partly explained by the large amount of total N applied in BioSludgehigh compost, but most likely the difference was due to an unexplained yield de- crease with Mineralhigh. Red clover has a considerable effect on yield within grass-clover leys. The clover yield increases with decreasing inorganic N supply in soil, and with increasing inorganic N amounts grasses are more competitive against clover (Boller and Nösberger 1987). In the study of Lynch et al. (2004), sew- age sludge compost produced N uptakes equal to fertilization with liquid manure, manure compost, corn-silage compost or ammonium nitrate fertilizer applied to clover-timothy mixture. In timothy mo- noculture fertilized with sewage sludge compost, they found lower N uptakes. In our organic grass- clover ley, the total plant biomass and N uptake tended to be lower with Biowaste and higher with BioSludge when compared with Manure. The N availability from BioSludge compost was appar- ently low, since the yields of grass and clover were close to those in the unfertilized control and the clover yield was higher than with other composts. We found the highest BNF estimates, up to 155 kg, with the lowest amount of compost N applied. These BNF estimates were higher than the highest BNF 67 kg N ha-1 previously found on active or- ganic farms in Finland. Our estimates were closer to previous BNF estimates of 90–114 kg N ha-1 in experimental fields (Väisänen et al. 2000), al- though in field-scale BNF in organic grass-clover leys may be also highly variable, ranging from 20 up to 250 kg N ha-1 within a field (Nykänen et al. 2008). In agreement with our results, Lynch et al. (2004) found that in legume-grass forage fertilized with compost containing a low amount of inorganic N, the BNF was close to the level obtained in un- fertilized legume-grass. Utilization of N The ANU was generally the same between the two fertilization levels each year, but in the first A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 70 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 71 year the increases of ANU appeared to follow the increases of inorganic N added in fertilizer. The ANUOM estimated for the compost application year remained below 10 kg N ha-1 for all treatments, suggesting rather low mineralization in soil. The negative estimates of ANUOM were found when the fertilized ANU was lower than the amount of inorganic N added in fertilizer, suggesting that part of the inorganic N applied in fertilizer was not harvested in the crops. In the second and third year after application the negative ANU values found in grass-clover ley were due to high yields in the unfertilized ley. This was particularly evident with ANU of the clover fraction. Accordingly, in previous studies the grass-clover yields in organically man- aged fields were generally good without additional fertilization (Nykänen et al. 2000). The higher ANU in the grass of Manure-fertilized grass-clover ley compared with other fertilizations reflected increased grass N uptakes in both cuts with Manure. The high positive values of N balance over three years reflected surplus of N due to the high amount of organic N applied in composts, whereas the clearly negative N balances in unfertilized soils indicated shortage of N in soil. The most prefer- able balances would be small positive values which were found with Biowaste and low fertilization in both conventional and organic systems. Previously, in organic grass-clover leys with BNF as a sole N input, the N balances were mostly negative after two years of cultivation if the yields were removed from the field (Nykänen 2008). There, the conclu- sion was that the N input in organic systems should remain higher than N output in order to maintain positive but not excessively high N balances. Efficiency of N utilization In the first year after compost application, we found the efficiency of compost N utilization to be 5–12% in the conventional and 2–8% in the organic experi- ment. These N recoveries were close to the overall range of 5–15% with various composts during the application year presented by Amlinger et al. (2003) in their review. Increasing the amount of inorganic N applied in composts is likely to increase the N recovery (Svensson et al. 2004), as inorganic N is directly available to plants whereas the rest of compost N is available to plants only after miner- alization. Eghball and Power (1999a) considered the N availability of 20% from composted feedlot manure to be lower than expected, whereas from uncomposted manure they estimated a 38% N avail- ability during the first year. In their study, part of the low N availability may have been caused by the lower amount of inorganic N applied in compost than in uncomposted manure, but apart from that application in autumn may have decreased the N availablity. The N available from composts has been clearly lower than that from mineral fertilizer (Zhel- jazkov et al. 2006), although the crop N recovery may underestimate the mineralization from organic amendments (Lynch et al. 2004). Accordingly, our N recoveries less than 12% with composts were consistently lower than the over 50% N recovery with Mineral fertilization. Similarly to Iglesias-Jimenez and Alvarez (1993), we found a trend of highest N efficiencies with the lowest compost applications in the first year. This was due to only slightly increased, but not doubled ANU with doubled N addition in high compost fertilization. The higher N recovery in the grass experiment compared with the grass-clover experiment was caused by different crops, as the N uptake of barley-grass was higher than that of bar- ley nurse crop. We determined the dosage of com- posts on the basis of categorical assumption of P fertilization effect of composts, which in most cas- es led to total N amounts exceeding the limit of the EU nitrate directive (Council of State 931/2000). If the upper limit of 250 kg total N ha-1 for silage crops had been followed in the grass experiment, it would have been possible to apply 90, 61, 46 and 30% of the amounts of Biowastelow, BioSludgelow, Biowastehigh and BioSludgehigh, respectively. In that case, the amount of nutrients supplied into soil would have decreased correspondingly and the yields could probably have been lower during the first year. The N recovery for biannually applied feedlot manure compost has been estimated to decrease from 15% in the application year to 8% in the sec- ond year in corn production (Eghball and Power 1999b). Accordingly, we found decreasing com- post N recovery in the organic experiment from the A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 72 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 73 first to the second year, although in our experiments the harvested crops varied between those years. From the second to the third year the N recovery in grass of the organic ley generally increased due to increased ANU in the compost-fertilized grass. In the conventional grass ley the increase of compost N recovery from the first to the second year was probably due to supplemental mineral fertilization, whereas the decrease from the second to the third year was mostly due to increased N uptake in the unfertilized grass ley. The efficiency of compost N utilization has been estimated often as an average N recovery over a multi-year period where compost has been ap- plied once in two years or with variable frequency (Eghball and Power 1999b, Hartl and Erhart 2005). However, the multi-year approach does not show possible changes between or within years. Lynch et al. (2004) estimated the fertilizer N recovery at the level of forage cuts, presenting the difference of N uptake in fertilized and unfertilized crop (which is equivalent to ANU) in proportion to the cumu- lative amount of total N applied before that cut. Correspondingly, we assumed that previous total N additions in fertilizer into the soil were included in the N supply for plants, but apart from that we subtracted the previous plant ANUs from the total fertilizer N supply. Lynch et al. (2004) found that in the year following the last compost fertilization of timothy forage the N recoveries ranged from slightly immobilized (−1%) up to 8%. In the sec- ond and third year in the organic grass-clover ley, we found nearly the same range of N recovery in grass, from −7% up to 8%. Due to annual mineral N additions our N recoveries in the conventional grass ley were clearly higher, up to 42% in the sec- ond year and 28% in the third year. Basically, we used the estimated BNF in the or- ganic grass-clover ley as N input in the N recovery estimations for the second and third experimental year. Because the estimated BNF was, in fact, equal to the clover N uptake, we reduced both BNF and clover N uptake from the N recovery estimation. In case we had measured BNF directly, for example by the N15 method (Sikora and Enkiri 2001), the accurate BNF might have been lower than the clo- ver N uptake. In that case, the estimate of compost N recovery in grass-clover ley might have been higher, because part of clover N would have origi- nated from the composts. The transfer of clover- fixed N to grasses is difficult to quantify and clover N mostly releases to the soil only after ploughing of ley (Hoegh-Jensen 2006, Hakala and Jauhiai- nen 2007). Therefore, considering the BNF as an immediate N input to the soil during the ongoing growing period might have been inaccurate. The NUE over three years was highest with low total N inputs and inversely proportional to the N balance values. Accordingly, in previous results of organic cereals fertilized with incorporation of grass-clover ley into the soil, the lowest NUEs were found with higher N input or lower N uptake (Nykänen 2008). The utilization and efficiency of fertilizer N may be assessed by various methods, but the dif- ferent scopes and boundaries of these methods should be clarified, particularly when organic fer- tilizers are considered. The estimates of N balance and NUE could be appropriate for assessing the utilization of N in a certain cropping system over several years. When the utilization of fertilizer N should be separated from the background effect of that particular soil, the estimate of ANU could be applied. The ANUs may be calculated annually or more frequently and a certain fertilization can be compared between various locations. The estimates for efficiency of N utilization, for example N re- covery, clarify the effect of fertilizer N in relation to the amount of total N in the fertilizer and allow comparisons between various fertilizers in variable conditions. However, the N recovery of organic fertilizers might be underestimated, while the N recovery of mineral fertilizers is typically high. Conclusions In mature municipal waste composts the majority of total N is in organic form leaving less than 10% as inorganic N. Yield response and the efficiency of N utilization during the application year increase with increasing supply of inorganic N in compost, A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 72 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 73 whereas a high amount of total N alone might not give yield responses. The recovery of compost N is usually much lower than that of mineral fertiliza- tion, with maximum recovery of 12% in the present study. In organic grass-clover ley established with waste composts the N recovery may be close to that with manure compost. In the organic ley, increase of clover yield may compensate for low grass yield, whereas high supply of inorganic N might be unfavourable for clover. Single application of compost with less than 25 Mg ha-1 may produce equal yields and N uptakes as doubled amounts of composts. Furthermore, based on N balance and estimates of N use efficiency, smaller applications of composts are most suitable for both conventional and organic ley in the long run. Waste composts may be supplemented with either moderate inorganic N additions or N fixation of clover. However, the optimal level of compost application and supplemental fertilization is case- specific, varying according to the characteristics of the compost and crop in question. The various estimates describing utilization of N should be interpreted with consideration of the scopes and boundaries of these methods. Moreover, a sub- stantial part of compost N may be released only after the application year and, therefore, the annual estimation of N efficiency in the following years should include the residual of the previously added, unused total N. Acknowledgements.The experimental work was funded by the Finnish Ministry of Agriculture and Forestry, the Finnish Ministry of the Environment and MTT Agrifood Research Finland. We sincerely thank all the persons in- volved in the field and laboratory work conducted at MTT Agrifood Research Finland, and especially Keijo Lehtonen, D.Sc. (Chem.), for his valuable contribution to this work and biometricians Timo Hurme and Lauri Jauhiainen for their advice in the statistical analyses of the data. We also thank Assistant Professor Kari Hänninen (University of Jyväskylä, Environmental Science) for useful comments during the preparation of this paper, Sevastiana Ruusamo, M.A., for revision of the English manuscript and all other associates for their invaluable contributions to the revi- sions of this manuscript. The preparation of this paper was financially supported by the Finnish Graduate School for Environmental Science and Technology (EnSTe) and the Finnish Cultural Foundation. References Agricultural Research Centre of Finland 1986. Soil and Plant Analysis. Agricultural Research Centre, Depart- ment of Soil Science. Jokioinen, Finland: 45 p. Amlinger, F., Götz, B., Dreher, P., Geszti, J. & Weissteiner, C. 2003. Nitrogen in biowaste and yard waste compost: dynamics of mobilisation and availability-a review. Eu- ropean Journal of Soil Biology 39: 107–116. Antikainen, R., Lemola, R., Nousiainen, J.I., Sokka, L., Esala, M., Huhtanen, P. & Rekolainen, S. 2005. Stocks and flows of nitrogen and phosphorus in the Finnish food production and consumption system. Agriculture, Ecosystems & Environment 107: 287–305. Boller, B.C. & Nösberger, J. 1987. Symbiotically fixed ni- trogen from field- grown white and red clover mixed with ryegrasses at low levels of15N-fertilization. Plant and Soil 104: 219–226. Cassman, K.G., Dobermann, A. & Walters, D.T. 2002. Agroecosystems, nitrogen-use efficiency, and nitro- gen management. Ambio 31: 132–140. Council of State 931/2000. Government Decree on the restriction of discharge of nitrates from agriculture into waters. Original in Finnish: Valtioneuvoston asetus maataloudesta peräisin olevien nitraattien vesiin pää- syn rajoittamisesta. Translation available in English at Internet: http://www.finlex.fi/en/laki/kaannokset/2000/ en20000931.pdf (Cited 20.12.2007). Debosz, K., Petersen, S.O., Kure, L.K. & Ambus, P. 2002. Evaluating effects of sewage sludge and household compost on soil physical, chemical and microbiological properties. Applied Soil Ecology 19: 237–248. Eghball, B. & Power, J.F. 1999a. Composted and noncom- posted manure application to conventional and no-till- age systems: corn yield and nitrogen uptake. Agrono- my Journal 91: 819–825. Eghball, B. & Power, J.F. 1999b. Phosphorus- and nitro- gen-based manure and compost applications: Corn production and soil phosphorus. Soil Science Society of America Journal 63: 895–901. Epstein, E. 1997. The Science of Composting. Lancaster, Basel: Technomic Publishing. 482 p. Erhart, E., Hartl, W. & Putz, B. 2005. Biowaste compost affects yield, nitrogen supply during the vegetation pe- riod and crop quality of agricultural crops. European Journal of Agronomy 23: 305–314. Fauci, M.F. & Dick, R.P. 1994. Plant response to organic amendments and decreasing inorganic nitrogen rates in soils from a long-term experiment. Soil Science So- ciety of America Journal 58: 134–138. Gabrielle, B., Da-Silveira, J., Houot, S. & Michelin, J. 2005. Field-scale modelling of carbon and nitrogen dynamics in soils amended with urban waste com- posts. Agriculture, Ecosystems & Environment 110: 289–299. Gagnon, B., Simard, R.R., Robitaille, R., Goulet, M. & Ri- oux, R. 1997. Effect of composts and inorganic fertiliz- ers on spring wheat growth and N uptake. Canadian Journal of Soil Science 77: 487– 495. Hakala, K. & Jauhiainen, L. 2007. Yield and nitrogen con- centration of above- and below-ground biomasses of A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 74 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 75 red clover cultivars in pure stands and in mixtures with three grass species in northern Europe. Grass and Fo- rage Science 62: 312–321. Hänninen, K., Koivula, N., Miikki, V., Urpilainen, S. & Räikkönen, T. 2001. Source separation and compost- ing of biowaste with a view to recycling of the end prod- uct. Jyväskylän yliopiston biologian laitoksen tiedo- nantoja 73. 29 p. Hänninen, K. & Mäkelä-Kurtto, R. 1995. Erilliskerätyn biojätteen aumakompostointi ja kompostin käyttökel- poisuus. Pääkaupunkiseudun julkaisusarja C 1995:17. 57 p. Hartl, W. & Erhart, E. 2005. Crop nitrogen recovery and soil nitrogen dynamics in a 10-year field experiment with biowaste compost. Journal of Plant Nutrition and Soil Science 168: 781–788. Hoegh-Jensen, H. 2006. The nitrogen transfer between plants: An important but difficult flux to quantify. Plant and Soil 282: 1–5. Houot, S., Clergeot, D., Michelin, J., Francou, C., Bour- geois, S., Caria, G. & Ciesielski, H. 2002. Agronomic value and environmental impacts of urban composts used in agriculture. In: Insam, H. et al. (eds.) Microbiol- ogy of Composting. Berlin Heidelberg New York: Sprin- ger-Verlag. p. 457– 472. Iglesias-Jimenez, E. & Alvarez, C.E. 1993. Apparent avail- ability of nitrogen in composted municipal refuse. Biol- ogy and Fertility of Soils 16: 313–318. Jakobsen, S.T. 1995. Aerobic decomposition of organic wastes 2. Value of compost as a fertilizer. Resources, Conservation and Recycling 13: 57–71. Jokinen, R. 1990. Effect of phosphorus precipitation chemicals on characteristics and agricultural value of municipal sewage sludges: 1. Characteristics of Ca, Al and Fe precipitated sewage sludges. Acta Agriculturae Scandinavica 40: 123–129. Keeling, A.A., McCallum, K.R. & Beckwith, C.P. 2003. Mature green waste compost enhances growth and nitrogen uptake in wheat (Triticum aestivum L.) and oilseed rape (Brassica napus L.) through the action of water-extractable factors. Bioresource Technolo- gy 90: 127–132. Kenward, M.G. & Roger, J.H. 1997. Small sample infer- ence for fixed effects from restricted maximum likeli- hood. Biometrics 53: 983–997. Koivula, N., Hänninen, K.I. & Tolvanen, O.K. 2000. Win- drow composting of source separated kitchen biow- astes in Finland. Waste Management & Research 18: 160–173. Littell, R.C., Milliken, G.A., Stroup, W.W., Wolfinger, R.D., & Schabenberger, O. 2006. SAS for Mixed Models, Sec- ond Edition. Cary, NC: SAS Institute Inc. 814 p. Lynch, D.H., Warman, P.R. & Voroney, R.P. 2004. Nitro- gen availability from composts for humid region peren- nial grass and legume-grass forage production. Journal of Environmental Quality 33: 1509–1520. Mamo, M., Rosen, C.J. & Halbach, T.R. 1999. Nitrogen availability and leaching from soil amended with mu- nicipal solid waste compost. Journal of Environmental Quality 28: 1074–1082. Mulvaney, R.L. 1996. Extraction of exchangeable am- monium and nitrate. In: Sparks, D.L. (ed.). Methods of Soil Analysis: Part 3. Madison, Wisconsin: Soil Science Society of America and American Society of Agrono- my. p. 1129–1131. Nykänen, A. 2008. Nitrogen dynamics of organic farm- ing in crop rotation based on red clover (Trifolium prat- ense) leys. Agrifood Research Reports 121: 60 p. + 4 app. Diss.: University of Helsinki, 2008. (Doctoral Dis- sertation). Available at internet: http://www.mtt.fi/met/ pdf/met121.pdf (Updated 15.4.2008) Nykänen, A., Granstedt, A., Laine, A. & Kunttu, S. 2000. Yields and clover contents of leys of different ages in organic farming in Finland. Biological Agriculture & Horticulture 18: 55–66. Nykänen, A., Jauhiainen, L., Kemppainen, J. & Lindström, K. 2008. Field-scale spatial variation in soil nutrients and in yields and nitrogen fixation of clover-grass leys. Agricultural and Food Science 17: 376–393. Rantala, P.R., Vaajasaari, K., Juvonen, R., Schultz, E., Joutti, A. & Mäkelä-Kurtto, R. 1999. Composting of for- est industry wastewater sludges for agricultural use. Water Science and Technology 40: 187–194. Sikora, L.J. & Enkiri, N.K. 1999. Fescue growth as affect- ed by municipal compost fertilizer blends. Compost Sci- ence & Utilization 7: 63–69. Sikora, L.J. & Enkiri, N.K. 2001. Uptake of 15N fertilizer in compost-amended soils. Plant and Soil 235: 65–73. Smith, S.R., Woods, V. & Evans, T.D. 1998. Nitrate dy- namics in biosolids-treated soils. II. Thermal-time mod- els of the different nitrogen pools. Bioresource Tech- nology 66: 151–160. Stratton, M.L., Barker, A.V. & Rechcigl, J.E. 1995. Com- post. In: Rechcigl, J.E. (ed.). Soil amendments and en- vironmental quality. Boca Raton, New York, London, Tokyo: CRC, Lewis Publishers. p. 249–309. Sullivan, D.M., Bary, A.I., Thomas, D.R., Fransen, S.C. & Cogger, C.G. 2002. Food waste compost effects on fertilizer nitrogen efficiency, available nitrogen, and tall fescue yield. Soil Science Society of America Journal 66: 154–161. Svensson, K., Pell, M. & Odlare, M. 2004. The fertilizing effect of compost and biogas residues from source separated household waste. Journal of Agricultural Science 142: 461– 467. Tognetti, C., Mazzarino, M. & Laos, F. 2007. Cocompost- ing biosolids and municipal organic waste: effects of process management on stabilization and quality. Bio- logy and Fertility of Soils 43: 387–397. Väisänen, J. 2000. Biological nitrogen fixation in organ- ic and conventional grass-clover swards and a model for its estimation. University of Helsinki, Department of Plant Production. Licentiate’s thesis. 42 p + 2 app. Väisänen, J., Nykänen, A. & Granstedt, A. 2000. Es- timation of biological nitrogen fixation in Finnish or- ganic grasslands. Grassland Science in Europe 5: 530–532. Venelampi, O., Weber, A., Rönkkö, T. & Itävaara, M. 2003. The biodegradation and disintegration of paper prod- ucts in the composting environment. Compost Science & Utilization 11: 200–209. Watson, C.A., Bengtsson, H., Ebbesvik, M., Løes, A., Myr- beck, A., Salomon, E., Schroder, J. & Stockdale, E.A. 2002. A review of farm-scale nutrient budgets for or- ganic farms as a tool for management of soil fertility. Soil Use and Management 18: 264–273. A G R I C U L T U R A L A N D F O O D S C I E N C E Tontti, T. et al. Waste composts as fertilizers 74 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 18 (2009): 57–75. 75 Westerman, P.W. & Bicudo, J.R. 2005. Management con- siderations for organic waste use in agriculture. Biore- source Technology 96: 215–221. Zheljazkov, V.D., Astatkie, T., Caldwell, C.D., MacLeod, J. & Grimmett, M. 2006. Compost, manure, and gyp- sum application to timothy/red clover forage. Journal of Environmental Quality 35: 2410–2418. SELOSTUS Jätekompostit rehunurmen lannoitteena Tiina Tontti, Arja Nykänen ja Miia Kuisma Maa- ja elintarviketalouden tutkimuskeskus Heinänurmi ja apila-heinänurmi perustettiin suojavil- jaan keväällä 2000 ja lannoitettiin perustamisvaiheessa biojätekompostin tai biojäte-puhdistamolietekompostin kahdella eri tasolla. Tavanomaisella heinänurmella verrannelannoitteena käytettiin väkilannoitetta ja luon- nonmukaisella apila-heinänurmella käytettiin karjanlan- takompostia. Suojaviljasta ja nurmista mitattiin sadot, typpisadot sekä maan liukoisen typen (NH4, NO3) pitois- uudet vuosina 2000–2002. Lisäksi apila-heinänurmen apilasadon avulla määritettiin biologisen typensidonnan määrä. Toisen ja kolmannen vuoden aikana tavano- maiselle heinänurmelle annettiin typen ja kaliumin lisälannoitus lannoitussuosituksen mukaisesti. Typen hyödyntämisen tehokkuutta arvioitiin vuosittain kahdella menetelmällä, typen hyväksikäyttöasteen (N recovery) ja kasvien saatavilla olevan typen määrän (ABN) arvioin- nin avulla. Typen hyödyntämistä kolmivuotisen jakson aikana arvioitiin typen peltotaseen (N balance) ja typen käytön tehokkuuden (NUE) avulla. Kompostien kokonaistypestä alle 10% oli liukoisessa muodossa ja kompostitypen hyväksikäyttöaste ensim- mäisen vuoden kasvisatoon vastasi suurimmillaankin biojätekompostilannoituksella alle 12% kompostien kokonaistypestä. Suojaviljan kuiva-aine- ja typpisato sekä typen hyväksikäyttöaste kasvoivat kompostilan- noituksessa annetun liukoisen typpimäärän kasvaessa ja kompostikäsittelyt lisäsivät satoja lannoittamattomaan kontrolliin verrattuna. Toisen ja kolmannen koevuoden aikana biojätekompostilla lannoitetun apila-heinänurmen sato oli alhaisempi kuin lantakompostilannoituksella. Toisaalta biojäte-puhdistamolietekompostilla lannoitetun seosnurmen apilasato oli suurempi ja kokonaissato yhtä suuri kuin lantakompostilannoituksella. Ensimmäisen vuoden alhaisella kokonaistyppilannoituksella typen hyväksikäyttöaste toisen ja kolmannen vuoden aikana saattoi olla suurempi ja vuotuinen sadontuotto yhtä suuri kuin suuremmalla kompostilannoituksella. Kolmen vuoden typpitaseet olivat yleensä positiivisia ja joissakin tapauksissa hyvinkin suuria, sillä kompostilannoituksissa annettiin suuri määrä orgaanista kokonaistyppeä josta vain osa korjattiin kasvuston typpisadossa. Typpitase oli positiivinen ja lähinnä tasapainotilannetta alhaisella lan- noitustasolla sekä biojätekompostilannoituksella. Typen käytön tehokkuus (NUE) oli kääntäen verrannollinen typpitaseisiin, sillä pienemmällä kompostilannoituksen määrällä saatiin suurempi typen käytön tehokkuus ja likimain sama typpisato kuin suuremmalla komposti- lannoituksella. Jätekomposteja voi käyttää rehunurmen lannoitukseen ja täydentää kompostilannoitusta väkilan- noitteella tai apilan typensidonnan avulla. Waste composts as nitrogen fertilizers for forage leys Introduction Material and methods Results Discussion Conclusions References SELOSTUS