Agricultural and Food Science in Finland 121 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 I N F I N L A N D Vol. 9 (2000): 121–134. © Agricultural and Food Science in Finland Manuscript received October 1999 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 I N F I N L A N D Vol. 9 (2000): 121–134. Timing of primary growth harvest affects the yield and nutritive value of timothy-red clover mixtures Marketta Rinne Agricultural Research Centre of Finland, Animal Production Research, FIN-31600 Jokioinen, Finland, e-mail: marketta.rinne@mtt.fi Arja Nykänen Agricultural Research Centre of Finland, Resource Management Research, FIN-51900 Juva, Finland, e-mail: arja.nykanen@mtt.fi The effects of partition of growth time between primary growth and regrowth of perennial organically grown mixed (mainly timothy and red clover) leys were studied over two years in Juva, Finland. Primary growth was harvested at three different dates and regrowth on a single occasion from all plots. Dry matter (DM) yield of primary growth increased by 116 kg per ha per day by delaying harvest (P<0.001) which was partly compensated by a reciprocal effect in the regrowth. Harvesting schedules had no effect on the botanical composition of herbage within harvests, but the proportion of red clover was lower in the primary growth (0.28) than in the regrowth (0.71). The proportion of red clover in weighted total yield decreased linearly from 0.46 to 0.35 (P<0.01) by delaying the primary growth harvest. The nutritional quality of timothy and red clover declined with advances in primary growth, the extent of which was greater for timothy. Digestible organic matter content in DM (D-value) decreased 2.6 and 5.6 g/kg per day in red clover and timothy, respectively. Reciprocal effects were observed in regrowth. However, the total yield and quality from both harvests was strongly influenced by prima- ry growth, since it accounted for on average 0.68 of total yield and differences in the nutritional quality of regrowth were smaller than for primary growth. Key words: botanical composition, chemical composition, digestibility, growth stages, maturity, mor- phology, Phleum pratense, Trifolium pratense Introduction Use of forages for animal production is depend- ent on attaining a high dry matter (DM) yield and maximising forage nutritional quality. Since these primary factors are in direct conflict, for- age production is essentially a compromise be- tween yield and quality. It is well documented that increases in DM yield of primary growth are accompanied by a decrease in herbage di- gestibility and nutrient concentrations (see Van mailto:marketta.rinne@mtt.fi 122 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 I N F I N L A N D Rinne, M. & Nykänen, A. Effects of harvesting strategy on organically grown leys Soest 1994). Forage digestibility has a profound effect on animal production. Based on 8 studies, milk production of cows fed grass silage based diets was reported by Huhtanen (1994) to de- crease on average by 0.26 kg/day for each in- cremental 10 g/kg decline of digestible organic matter (OM) content in DM (D-value). Regulations on organic production require that forages comprise 0.60 of daily DM con- sumption of cattle (0.50 is acceptable for 3 months at the beginning of lactation) and the feeds should preferably be produced at the same farm where they are used (European Union 1999). This places restrictions on the use of con- centrate feeds to compensate for sub-optimal forage quality or quantity which may lead to substantial losses in milk production. Thus, im- plementation of an optimal harvesting strategy is even more important for organic than conven- tional farming. Forage leys are harvested several times dur- ing the growing season and therefore studies concentrating only on primary growth are inad- equate. Under Finnish climatic conditions, typi- cally only two or occasionally three cuts of grass can be harvested within a year. For mixed leys containing clover, such as organically grown leys, generally only two harvests are obtained. The development of leys is slower in regrowth compared to primary growth (Syrjälä and Ojala 1978, Pulli 1980, Huokuna and Hakkola 1984, Bélanger and McQueen 1998, 1999), but the residual effects of primary cutting date on sub- sequent harvest(s) must also be considered. Stud- ies where the growing time has been differen- tially allocated between primary growth and re- growth are limited. This approach is however, relevant at the farm level, because the harvest of regrowth under Finnish conditions is often optimized based on overwintering ability of the leys rather than forage quality. Forage legumes are essential components of organic production. The biological nitrogen (N) fixation ability of Rhizobium-bacteria in symbi- osis with legume roots is the basis of N supply to the farm nutrient cycle. Legumes (in Finnish conditions mainly red clover) are usually grown as mixtures with grasses, but the different char- acteristics of legumes and grasses further com- plicate the choice of harvesting strategy. The current experiment was designed to elu- cidate the effects of partition of growth time in a two-cut system on forage quantity and quality. Perennial grass-clover leys were managed un- der organic conditions, but results may also be applicable to conventional forage production practises. Direct comparisons between organic and conventional leys in relation to forage pro- duction were not found and may be difficult to interpret, since the differences in farming sys- tems are likely to affect forage production through changes in, for example, soil N status and the proportion of different plant species. The mutual dynamics and individual properties of two important plant species, timothy and red clover, grown as a mixed sward, were evaluat- ed. Timothy and red clover are usually grown for animal feeds, and therefore results are dis- cussed in context to animal production. Prelim- inary results from the first year of the study have previously been presented (Rinne et al. 1996). Material and methods Leys were grown under organic conditions at Partala Research Station (62°N) of the Agricul- tural Research Centre of Finland on fine sand moraine soil (3–6% OM, pH (CaCl2) 6.3–6.8). The seed mixture was comprised of timothy (Phle- um pratense cv. Bottnia 2; 10 kg/ha), meadow fescue (Festuca pratensis cv. Kalevi; 6 kg/ha) and red clover (Trifolium pratense cv. Bjursele; 4 kg/ha). In 1995, two main plots (one and two year old leys) were used. The same plots were utilized the following year with an additional main plot of a one year old ley. The plots uti- lized in the present experiment were part of a larger experiment described by Nykänen et al. (2000). Partition of growth time between primary growth and regrowth was studied in a two-cut 123 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 I N F I N L A N D Vol. 9 (2000): 121–134. system. Main plots were divided into three sub- plots (10 m2) which were harvested at three dif- ferent dates in primary growth, each with three replicates. Regrowth was simultaneously har- vested from all plots (Table 1). For maximal uti- lization of the growing season, regrowths were harvested at the end of August, a time consid- ered optimal for overwintering of the leys. Plots were harvested with an experimental grass plot harvester, grass yield was measured, and representative samples were collected for laboratory analysis. Samples were dried at 105°C for 20 h for DM determination. Botanical com- position of the samples was determined from a representative sample weighing at least 0.5 kg. After botanical separation, the main species, tim- othy and red clover were fractionated into leaves, stems and inflorescenses. Leaf sheaths in timo- thy and leaf stalks in red clover were included in the stem fraction. Botanical and morphologi- cal fractions were dried in 60°C until dry to cal- culate their proportions on a DM basis. Then the leaf and stem fractions of timothy and red clo- ver from the three replicates were combined for subsequent analysis. The ash content of the leaves and stems was determined in a muffle furnace at 550°C for 6 h. Total N content was measured by the Dumas method using a Leco FP-428 N analyzer and crude protein (CP) content was calculated as 6.25 × N. Neutral detergent fibre (NDF) was deter- mined according to Robertson and Van Soest (1981) and in vitro OM digestibility assessed by cellulase solubility (Friedel 1990). D-value was calculated as (1000 – ash con- tent) × OM digestibility and the metabolizable energy (ME) content of the fractions as 0.0169 × D-value – 1.05 (MAFF 1975). The value of dietary protein defined as amino acids absorbed from the small intestine (AAT) and protein bal- ance in the rumen (PBV) were calculated accord- ing to the Finnish protein evaluation system (Madsen et al. 1995, Tuori et al. 1996). An ef- fective rumen degradability of protein of 0.75 was assumed for all samples. Digestible crude carbohydrate content was calculated as (1000 – ash content – CP content – ether extract content) × OM digestibility. Ether extract content was not determined, but values of 20 and 30 g/kg DM were assumed for timothy and red clover frac- tions, respectively. No corrections in AAT val- ues were made for negative PBV values. Com- position of whole plants was reconstituted ne- glecting the contribution of inflorescenses, and Table 1. Cutting dates and description of growing seasons. 1995 1996 Date Days1) CT1,2) CR1,3) Date Days CT CR Primary growth I4) 13 June 28 316 29 17 June 48 245 78 II 21 June 36 410 49 26 June 57 308 103 III 29 June 44 496 52 8 July 69 408 151 Regrowth I 28 August 77 790 114 19 August 64 582 156 II 28 August 69 694 96 19 August 55 521 131 III 28 August 61 604 91 19 August 43 424 83 1) Cumulated since the onset of growth in the spring for primary growth, and since the harvest of primary growth for regrowth 2) Mean daily temperature –5°C 3) Rainfall (mm) 4) I, II and III refer to the order of cutting dates in the primary growth 124 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 I N F I N L A N D Rinne, M. & Nykänen, A. Effects of harvesting strategy on organically grown leys the composition of total yield neglecting the con- tribution of other plant species, since these were not determined. Rate of digestion (k d ) in the rumen was meas- ured using a modified in vitro method of Theod- orou et al. (1994). Only samples from 1995 were analysed. Duplicate samples of 0.5 g were incu- bated in gas tight culture bottles with rumen flu- id and buffers. The volume of gas produced by bacterial fermentation was measured manually with a syringe at 3–12 h intervals, for a mini- mum of 11 times over a period of 3 d. The curve of cumulative gas production was fitted to the equation p = a + b(1-e-ct) (Ørskov and McDon- ald 1979), where a + b represents the cumula- tive gas production and c the rate of digestion. The cumulative gas production was not used to assess forage quality, because the volume of gas is greatly influenced by the chemical composi- tion of the substrate (fermentation of CP produc- es less gas than fermentation of carbohydrates) and the proportion of different fermentation gas- es. The cumulative temperature from the onset of growth in the spring [Σ(mean daily tempera- ture – 5°C)] is based on data collected from the nearby Finnish Meteorological Institute in Mikkeli, 40 km south west from the experimen- tal site. The onset of growth starts when the mean daily temperature rises above 5°C for 5 consec- utive days. Rainfall was measured at the exper- imental site (Table 1). Numerical values for daily changes of dif- ferent parameters were calculated according to linear regression equations. Experimental data was subjected to analysis of variance using the GLM procedure of SAS using the following model: y ijkl = µ + Y i + A j + C k + R l + e ijkl , where Y is the year (1–2), A is the age of the ley (1–3), C is the cutting time of primary growth (1–3) and R is the replicate (1–3). Primary growth, regrowth and total yield accross both harvests were analysed separately. Some inter- actions of “year × cutting time” and “age of the ley × cutting time” were found, but because these were in parameters of minor interest, they were not included in the final model. To study the ef- fect of “age of the ley” results were analysed separately for both years. Data concerning herb- age chemical composition was not subjected to statistical analysis because replicates were com- bined. The focus of this experiment was on har- vesting strategies and the results of “year” and “age of the ley” are not tabulated. Sums of squares for the effect of “cutting time of prima- ry growth” were separated using orthogonal con- trasts into single degree of freedom comparisons of linear (P L ) and quadratic (P Q ) trends. Results Postponing the harvest of primary growth in- creased DM yield of the leys (P L <0.001), but an opposite trend in the regrowth (P L <0.001) par- tially compensated for this response resulting in a markedly lower though significant (P L <0.05) effect in total DM yield (Table 2). The increase in DM yield of primary growth was 116 kg per ha per day when the harvest was postponed, but the decrease in regrowth was 79 kg such that the effect of timing of first cut on total yield was 37 kg per day per ha. Yields of digestible OM, ME and CP in primary growth and regrowth behaved similarly as DM yield except that no significant effects for total yield were found (P>0.05). The total DM yield was higher in 1995 than in 1996 (6011 vs. 5012 kg, P<0.001). In 1995, the proportion of primary growth was 0.73 of the total yield, while in 1996 it was 0.64. In gen- eral, the plants were in a later stage of develop- ment in 1995 than in 1996 during harvests of primary growth (lower proportion of leaves and D-value) despite earlier harvesting dates. In 1995 the one year old leys were less pro- ductive than two year old ones (5652 vs. 6370 kg DM; P<0.05). In 1996, the total DM yields for one, two and three year old leys were 4301, 5275 and 5461 kg, respectively (P L <0.01). Postponing the harvest of primary growth did 125 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 I N F I N L A N D Vol. 9 (2000): 121–134. not affect the botanical composition of primary growths and regrowths. The difference in botan- ical composition between primary growth and regrowth was remarkable especially in 1995 (Figure 1a and 1b), when the proportion of red clover was only 0.098 in primary growth but 0.747 in regrowth. Corresponding values in 1996 were 0.471 and 0.673, respectively. Although meadow fescue was included in the seed mix- ture, very little (on average 0.073) was found in harvested herbage. The red clover content of weighted total yield decreased as harvest of first cut was postponed (Figure 1c; 0.46, 0.43 and 0.35 for harvests I, II and III, respectively, P L <0.01). Age of the ley had only minor effects on the proportion of red clover in total yield [0.26 and 0.30 for one and two year old leys in 1995 (P<0.10) and 0.59, 0.51 and 0.55 for one, two and three year old leys in 1996 (P>0.10)]. Advances in the development of timothy and red clover with postponed harvest in primary growth were clearly indicated by changes in the morphological composition of the plants (Table 3). Changes were slower in red clover. For ex- ample, proportion of leaves in the primary growth decreased 0.0043 units per day in red clover and 0.0080 units in timothy. Reciprocal effects were identified in regrowth, the extent of which were more profound for red clover (the proportion of leaves increased by 0.0099 units per day in red clover and by 0.0026 units in tim- othy). Results from chemical analysis of leaf and stem fractions from the plants, reconstituted plants and reconstituted yields are presented in Table 4. Changes during primary growth were more rapid in timothy than red clover. The de- cline in D-value of timothy leaves (1.0 g/kg per Table 2. The effect of partition of growth time on DM, digestible organic matter, metabolizable energy and crude protein yields of organically grown leys. Cutting time in primary growth1) Statistical significance3) I II III SEM2) Linear4) Quadratic4) Dry matter yield (kg/ha) Primary growth 2780 3846 4951 121.5 *** NS Regrowth 2574 1681 1040 111.4 *** NS Total 5354 5527 5991 178.7 * NS Digestible organic matter yield (kg/ha) Primary growth 1883 2479 3006 85.9 *** NS Regrowth 1772 1191 743 76.0 *** NS Total 3655 3671 3750 123.2 NS NS Metabolizable energy yield (GJ/ha) Primary growth 28.9 37.8 45.5 1.33 *** NS Regrowth 27.2 18.4 11.5 1.15 *** NS Total 56.1 56.2 57.0 1.89 NS NS Crude protein yield (kg/ha) Primary growth 341 434 489 24.0 *** NS Regrowth 439 327 209 19.5 *** NS Total 781 761 699 32.3 o NS 1) Data averaged over 1 and 2 year old leys in 1995, and 1, 2 and 3 year old leys in 1996. 2) Standard error of the mean 3) NS (not significant); o (p < 0.10); * (p < 0.05); ** (p < 0.01); *** (p < 0.001) 4) Linear and qudratic trends of the timing of first harvest 126 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 I N F I N L A N D Rinne, M. & Nykänen, A. Effects of harvesting strategy on organically grown leys Fig. 1. The effect of cutting time of primary growth on bo- tanical composition of primary growth (a), regrowth (b) and weighted total yield (c) of organically grown leys in 1995 and 1996. Table 3. The effect of partition of growth time on morphological composition of timothy and red clover grown under organic conditions. Cutting time in primary growth1) Statistical significance3) I II III SEM2) Linear Quadratic Primary growth Timothy Leaves 0.376 0.258 0.228 0.0135 *** * Stems 0.582 0.651 0.672 0.0123 *** NS Inflorescenses 0.042 0.092 0.100 0.0037 *** *** Red clover Leaves 0.452 0.426 0.367 0.0125 *** NS Stems 0.549 0.574 0.624 0.0122 *** NS Regrowth Timothy Leaves 0.907 0.950 0.957 0.0131 * NS Stems 0.093 0.050 0.043 0.0103 * NS Red clover Leaves 0.395 0.520 0.601 0.0159 *** NS Stems 0.537 0.435 0.389 0.0187 *** NS Inflorescenses 0.068 0.045 0.011 0.0156 * NS 1) Data averaged over 1 and 2 year old leys in 1995, and 1, 2 and 3 year old leys in 1996. 2,3,4) see table 2 127 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 I N F I N L A N D Vol. 9 (2000): 121–134. Table 4. Concentrations (g/kg dry matter) of ash, neutral detergent fibre (NDF), crude protein (CP), digestible organic matter (D-value), amino acids absorbed from the small intestine (AAT), protein balance in the rumen (PBV) and rate of digestion (k d , 1/h; only for samples from 1995) in leaves, stems, reconstituted whole plants and reconstituted yields of organically grown leys (I, II and III represent the cutting time of the primary growth; each value is a mean of 5 observations except k d , which is a mean of 2 observations). Ash NDF CP D-value AAT PBV k d Primary growth Timothy leaves I 69 529 145 704 93 35 0.0646 II 70 550 141 695 92 33 0.0637 III 76 554 139 683 90 33 0.0622 Timothy stems I 56 688 70 676 80 -18 0.0490 II 47 739 52 610 71 -25 0.0424 III 42 745 45 542 63 -23 0.0423 Reconstituted timothy I 61 628 99 685 86 3 0.0542 I 53 686 77 633 78 -8 0.0474 III 50 697 69 579 72 -9 0.0459 Red clover leaves I 90 301 324 729 117 120 0.0680 II 88 339 295 718 112 99 0.0710 III 89 320 278 710 109 87 0.0677 Red clover stems I 105 377 137 702 90 -18 0.0769 II 86 443 105 672 83 -37 0.0756 III 71 487 92 633 78 -41 0.0760 Reconstituted red clover I 98 344 221 714 102 44 0.0730 II 86 401 186 690 96 20 0.0739 III 78 425 161 662 90 5 0.0730 Reconstituted yield of total primary growth I 72 543 135 691 92 18 0.0558 II 64 587 117 650 85 7 0.0511 III 57 605 98 606 79 2 0.0487 Regrowth Timothy leaves I 74 573 128 719 92 22 0.0655 II 73 557 127 723 92 22 0.0685 III 72 534 130 729 93 23 0.0677 Red clover leaves I 98 294 283 712 110 91 0.0663 II 96 305 289 711 111 96 0.0722 III 97 296 290 713 111 96 0.0713 Red clover stems I 73 447 104 665 83 -38 0.0810 II 82 409 106 696 86 -41 0.0809 III 92 388 116 704 88 -35 0.0789 Reconstituted red clover I 84 383 179 683 94 15 0.0736 II 90 350 207 706 100 34 0.0763 III 95 331 221 710 102 44 0.0743 Reconstituted yield of total regrowth I 83 412 171 689 94 17 0.0722 II 87 383 195 709 99 32 0.0749 III 90 375 202 714 100 41 0.0731 Reconstituted total yield I 76 480 154 690 93 18 0.0623 II 72 512 147 673 90 7 0.0576 III 64 548 129 631 83 2 0.0527 128 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 I N F I N L A N D Rinne, M. & Nykänen, A. Effects of harvesting strategy on organically grown leys day) was less than that of timothy stems (6.9 g/ kg per day). The respective values of decline in D-value per day for red clover were 0.8 g/kg in leaves and 3.5 g/kg in stems. These changes re- sulted in a daily decline in D-value of 5.6 and 2.6 g/kg for reconstituted timothy and red clo- ver, respectively. The nutritional value of timothy was lower than that of red clover in the primary cut. On average D-value and CP content were 634 and 82 g/kg DM in timothy and 689 and 200 g/kg DM in red clover. Because the proportion of red clover was small in the primary growth, the qual- ity of the reconstituted primary yield was high only for the first harvest date. In the regrowth, differences in the nutritional quality between plant species were smaller. On average D-value and CP content were 725 and 128 g/kg DM in timothy and 699 and 204 g/kg DM in red clover. Residual effects of date of harvest in primary growth were lower for the regrowth than differ- ences found in the quality of primary growth. Since primary growth represented the majority of herbage harvested, the marked decline in tim- othy quality in primary growth was discernible even in the reconstituted total yield for the whole growing season as the weighted D-value for har- vests I, II and III was 690, 673 and 631 g/kg DM, respectively. Timothy leaves were digested faster than stems (0.0654 vs. 0.0446 per h) while the reverse was true for red clover (0.0694 vs. 0.0782 per h). In general red clover was digested faster than timothy. Developmental effects on k d of morpho- logical fractions were minor and therefore clear trends in reconstituted timothy were primarily due to changes in the proportion of different morphological fractions. Discussion Herbage production Compromises in total DM yield were less than 700 kg/ha caused by early harvesting of prima- ry growth. Similar results were obtained when timing of first cut was manipulated in a 3-cut system (Syrjälä and Ojala 1978) or in a system where the number of cuts varied from 4 to 6 de- pending on the timing of the first cut (Frame 1987). Differences between early and late cuts of the primary growth were diminished to less than 100 kg/ha when compared on the basis of digestible OM yield. Digestible OM yield of forage is a more val- id criterion than DM yield when animal produc- tion is the ultimate goal of plant production, but this parameter also has limitations. High digest- ible OM yield may be achieved in situations of large DM yield even though the concentration of digestible nutrients may be low. The critical factor in terms of animal nutrition is the con- centration of digestible nutrients due to limited intake capacity of animals (Van Soest 1994). On grass silage based diets, a D-value around 700 g/kg can be recommended for milk production (Rinne et al. 1999a). In mixed leys, the proportion of red clover is generally lower in primary growth than in re- growth (0.40 vs. 0.60 without N fertilization re- ported by Hakkola and Nykänen-Kurki 1994). In cases of severe overwintering problems such as in 1995 in the present experiment, the pro- portion of red clover may be very low in prima- ry growth. Postponed harvest of primary growth did not increase the proportion of red clover for either year in the current study. Frame (1987) found that the proportion of white clover de- creased with postponed harvest when grown with ryegrass receiving either 0 or 80 kg N per hec- tare. In the two year trial of Fagerberg and Ek- bohm (1995), the proportion of red clover in- creased in the first year with postponed harvest of primary growth, but decreased in the second year. A stable but substantially higher red clo- ver content was obtained in regrowth. In practical feeding situations, it is often only possible to feed one silage at a time. If silages harvested from primary growth which consist mainly of grasses of low digestibility and low intake potential, and regrowth which consist mainly of legumes with high digestibility and 129 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 I N F I N L A N D Vol. 9 (2000): 121–134. intake potential are to be used, formulation of balanced rations to livestock becomes more dif- ficult. Benefits in the form of increased propor- tion of clover in herbage DM with postponed harvest of primary growth seem unrealistic. Development of digestibility Decrease of digestibility with advancing devel- opment of plants in primary growth is well es- tablished. Reported values (g/kg per day) for tim- othy vs. red clover (6.0 vs. 3.3, Salo et al. 1975; 5.1 vs. 1.7, Hakkola and Nykänen-Kurki 1994 (recalculated from ME content estimated accord- ing to the Menke gas production method); 3.1 vs. 1.9, Fagerberg and Ekbohm 1995 (recalcu- lated from ME content estimated using Near In- frared Spectroscopy) indicate that the decline is more rapid for grasses than for legumes, a find- ing consistent with the current data. In several data sets, digestibility of grasses was higher than that of legumes early in the growing period (Salo et al. 1975, Hakkola and Nykänen-Kurki 1994, Fagerberg and Ekbohm 1995). This observation can also be deduced from the current results by extrapolation of re- gression analysis presented in Figure 2a. Around typical harvest times, no great differences be- tween species may be found. However, the slow- er rate of decline of red clover allows more flex- ibility in harvesting strategy provided that red clover represents a significant proportion of herbage DM. Only small differences were found in the rate of decline in digestibility, when different spe- cies or varieties of temperate perennial grasses were compared (Salo et al. 1975, Salo 1978, Hides et al. 1983, Huokuna and Hakkola 1984, Cherney et al. 1993). However, no direct com- parisons of organic and conventional production could be found in the literature. The N supply to the grasses may be lower in organic farming, particularly in cases of low legume persistence. This situation was evident in our data in 1995, which resulted in very low CP contents of timo- thy. Several studies have indicated that the level of N fertilization has only minimal effects on grass digestibility, despite increases in CP con- tent (Huokuna and Hakkola 1984, Fagerberg and Ekbohm 1995). Salo (1978) observed no differ- ences in the daily decline in digestibility of per- ennial grasses (11.6, 11.8 and 11.1 g/kg per day when plots were fertilized with 0, 50 and 100 kg N/ha, respectively). However, Bélanger and McQueen (1998) observed a low rate of decline of 2.3 g/kg in N deficient grass (0 N), but clearly higher rates of 5.5, 4.6 and 4.8 g/kg in grasses receiving 70, 140 and 210 kg N/ha, respective- ly. The slow decline in digestibility of unferti- lized grass was mainly explained by a greater proportion of leaves in herbage DM (Bélanger and McQueen 1998). In a later study, Bélanger and McQueen (1999) concentrated on the digest- ibility development of timothy leaf and stem fractions under varying N nutrition. Leaf digest- ibility decreased slightly early in the growing season in response to N deficiency, but differ- ences in stem digestibility were not found. The decline in forage digestibility may not always be linear with respect to time (Poutiai- nen and Rinne 1971, Rinne et al. 1997, 1999b). Sanderson and Wedin (1989) and Bélanger and McQueen (1998) presented the development of digestibility of plants in relation to their pheno- logical development. Estimates of herbage qual- ity were accurate, but the use of phenological indexes is laborious and unsuitable for applica- tion on a farm level. Cumulative temperature appears to be a reasonably good predictor of plant development in primary growth at least under Finnish conditions (Pulli 1980, Huokuna and Hakkola 1984, Rinne et al. 1999b). Further- more, information derived from meteorological measurements reduces labour requirements com- pared to phenological analysis and therefore rep- resents a tool with great potential for practical application. In the current experiment, the decline in di- gestibility was linear with respect to time, but was subject to large between-year variations (Figure 2a). This variation can be decreased by presenting D-values in relation to cumulative 130 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 I N F I N L A N D Rinne, M. & Nykänen, A. Effects of harvesting strategy on organically grown leys temperature and the relationship still remains linear (Figure 2b). A good prediction can also be derived based on the proportion of leaves in total plant DM (Figure 2c). The clear decrease in the proportion of leaves appears to have accelerated the decline in timo- thy quality in primary growth whereas the high proportion of leaves probably contributed to the slower development in the regrowth. The slow- er decline in digestibility of leaves than stems with advances in grass development is well doc- umented (Terry and Tilley 1964, Davies 1976, Hides et al. 1983, Sanderson and Wedin 1989, Bélanger and McQueen 1999). Digestibility of stems may be even higher than that of leaves at early stages of development, but around the com- mon harvest time, digestibility of stems is clear- ly lower. In the data sets of Terry and Tilley (1964) and Sanderson and Wedin (1989), leg- umes were included. The development of lucerne exhibited a similar pattern to that described for grasses. The digestibility development of red clover was only studied by Sanderson and Wed- in (1989). The rate of decline in digestibility was greater in stems than leaves, but the digestibili- ty of leaves remained lower than that of stems during the total observation period. Declines in digestibility of ley regrowths is slower than that of primary growth (Syrjälä and Ojala 1978, Pulli 1980, Huokuna and Hakkola 1984, Bélanger and McQueen 1998, 1999). Due to higher DM yield and larger variations in pri- mary growth quality, the effects of postponed harvest of primary growth were even discerni- ble in the weighted composition of total yield. This was also noted by Syrjälä and Ojala (1978) and Frame (1987) using similar experimental designs. Consequences on animal feeding Inclusion of red clover in forage fed to dairy cows has resulted in higher milk production com- Fig. 2. Timothy and red clover D-values in primary growth as functions of growth time in days since the onset of growth in the spring (a), cumulative temperature (b) and propor- tion of leaves in dry matter (DM; c) in 1995 and 1996. 131 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 I N F I N L A N D Vol. 9 (2000): 121–134. pared to silage prepared entirely from grasses (Thomas et al. 1985, Randby 1992, Heikkilä et al. 1996). In all cases, the intake of silage con- taining red clover was greater than that of pure grass silage. Increasing digestibility of forage is generally associated with increased intake (Van Soest 1994), but in previously cited studies, dif- ferences in forage digestibilities were small. Legumes seem to have properties other than high digestibility that contribute to a high intake po- tential. The NDF concentration of legumes is lower than that of grasses, but the concentration of lignin is higher in legumes (Van Soest 1994). Possible intake promoting characteristics of leg- umes have been attributed to faster rates of di- gestion, passage and particle breakdown in the rumen (Smith et al. 1972, Grenet 1989, Van Soest 1994). These properties contribute to faster clear- ance of digesta from the rumen thus alleviating the constraint of physical fill on feed intake (Van Soest 1994). Higher k d of red clover compared to timothy was also observed in the current study. Although k d and digestibility were correlated, red clover fractions, primarily stems, had higher k d coefficients than timothy fractions of the same digestibility (Fig. 3). Legumes are generally higher in CP than grasses. Responses to increased protein supple- mentation appear to be independent of grass si- lage CP content irrespective of the methods used for its manipulation such as N application rates (Shingfield et al. 1999) or harvest date (Rinne et al. 1999a). In the present study, the contents of AAT and PBV were lower for timothy rela- tive to red clover. Information concerning the true protein value of grass vs. legume forages verified by animal production responses is lim- ited. Heikkilä et al. (1996) reported similar milk production responses to protein supplementation with silage containing clover compared to pure grass silage indicating that responses were not limited by the inclusion of legumes. Ease of indoor feeding of dairy cows would be improved, if forages harvested during sum- mer have similar D-values. In organic produc- tion, the D-value should be relatively high due to the limitations in concentrate feeding (Euro- pean Union 1999). These goals are best achieved when the primary growth of leys is harvested relatively early. If however, low D-value forage is produced due to postponed harvest of prima- ry growth, concentrate intake must be increased to maintain milk production or otherwise a de- crease in milk production has to be accepted (Rinne et al. 1999a). Fig. 3. Correlations between D- value and rate of digestion (k d ) of leaves and stems of red clover and timothy contained in primary growth and regrowth in 1995. 132 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 I N F I N L A N D Rinne, M. & Nykänen, A. Effects of harvesting strategy on organically grown leys Conclusions The nutritional quality of both timothy and red clover decreased with postponed harvest of pri- mary growth, but the extent of decline was great- er for timothy. However, later harvesting result- ed in higher DM yields. Reciprocal residual ef- fects in the regrowth were less profound. If the aim of forage production is to produce feed for intensive animal production, primary growths should be harvested early, because the poor qual- ity of primary growth influenced the quality of forage harvested across both growth periods. Cumulative temperature was a good predictor of herbage D-value in primary growth and it could be used to developed a practical application as- sisting in the choice of a correct harvesting time. Acknowledgements. We appreciate the contribution of Seppo Ahvenjärvi for digestion kinetics analysis. References Bélanger, G. & McQueen, R.E. 1998. Analysis of the nu- tritive value of timothy grown with varying N nutri- tion. Grass and Forage Science 53: 109–119. – & McQueen, R.E. 1999. Leaf and stem nutritive val- ue of timothy grown with varying N nutrition in spring and summer. Canadian Journal of Plant Science 79: 223–229. Cherney, D.J.R., Cherney, J.H. & Lucey, R.F. 1993. In vitro digestion kinetics and quality of perennial grass- es as influenced by forage maturity. Journal of Dairy Science 76: 790–797. Davies, I. 1976. Developmental characteristics of grass varieties in relation to their herbage production. 1. An analysis of high-digestibility varieties of Dactylis glomerata at three stages of development. Journal of Agricultural Science, Cambridge 87: 25–32. European Union 1999. European Union Official Journal L 222, 24 August 1999. Fagerberg, B. & Ekbohm, G. 1995. Variation in clover content and in nutritional value of grass-clover leys. In: Crop Production Science 23. Department of Crop Production Science, Swedish University of Agricul- tural Sciences, Uppsala, Sweden. 46 p. Frame, J. 1987. The effect of strategic fertilizer nitrogen and date of primary harvest on the productivity of a perennial ryegrass/white clover sward. Grass and Forage Science 42: 33–42. Friedel, K. 1990. Die Schätzung des energetischen Fut- terwertes von Grobfutter mit Hilfe einer Cellulase- methode. Wissenschaftliche Zeitung Universitet Ros- tock, N-Reihe 39: 78–86. Grenet, E. 1989. A comparison of the digestion and re- duction in particle size of lucerne hay (Medicago sati- va) and Italian ryegrass hay (Lolium italicum) in the ovine digestive tract. British Journal of Nutrition 62: 493–507. Hakkola, H. & Nykänen-Kurki, P. 1994. Effect of nitrogen fertilization and cutting time on the quality and vari- able cost of red clover and timothy herbage produc- tion. In: Mannetje, L. ‘t & Frame, J. (eds.). Grassland and Society. Proceedings of the 15th General Meet- ing of European Grassland Federation, Wageningen, The Netherlands, June 6–9, 1994. p. 105–108. Heikkilä, T., Toivonen, V. & Mela, T. 1996. Effects of red clover-grass, grass and annual ryegrass silages with two concentrate protein levels on milk production. In: Parente, G. et al. (eds.). Grassland and Land Use Systems. Proceedings of the 16th General Meeting of European Grassland Federation, Grado (Gorizia), Italy, September 15–19, 1996. p. 447–450. Hides, D.H., Lovatt, J.A. & Hayward, M.V. 1983. Influ- ence of stage of maturity on the nutritive value of Italian ryegrasses. Grass and Forage Science 38: 33– 38. Huhtanen, P. 1994. Forage influences on milk composi- tion. Proceedings of the Nova Scotia forage confer- ence; forage: seeding to feeding. The Nova Scotia Forage Council, Darthmouth, Nova Scotia. p. 144– 162. Huokuna, E. & Hakkola, H. 1984. Koiranheinän ja timo- tein kasvu ja rehuarvon muutokset säilörehuasteel- la. Tiedote 8/84. Maatalouden tutkimuskeskus, Jokio- inen. 54 p. Madsen, J., Hvelpund, T., Weisbjerg, M.R., Bertilsson, J., Olsson, I., Spörndly, R., Harstad, O.M., Volden, H., Tuori, M., Varvikko, T., Huhtanen, P. & Olafsson, B.L. 1995. The AAT/PBV protein evaluation system for ruminants. A revision. Norwegian Journal of Agri- cultural Sciences, supplement no 19. MAFF 1975. Energy allowances and feeding systems for ruminants. Technical Bulletin 33. Her Majesty’s Sta- tionery Office, London. 79 p. Nykänen, A., Granstedt, A., Laine, A. & Kunttu, S. 2000. The yields and clover contents of leys of different age in organic farming in Finland. Biological Agri- culture and Horticulture (in press). Ørskov, E.R. & McDonald, I. 1979. The estimation of pro- tein degradability in the rumen from incubation meas- 133 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 I N F I N L A N D Vol. 9 (2000): 121–134. urements weighted according to rate of passage. Journal of Agricultural Science, Cambridge 92: 499– 503. Poutiainen, E. & Rinne, K. 1971. Korjuuasteen vaikutus säilörehun ravintoarvoon. Kehittyvä Maatalous 3: 15–28. Pulli, S. 1980. Growth factors and management technique used in relation to the developmental rhythm and yield formation pattern of a pure grass stand. Journal of the Scientific Agricultural Society of Finland 52: 281– 330. Randby, Å.T. 1992. Grass-clover silage for dairy cows. Proceedings of the 16th General Meeting of Europe- an Grassland Federation, Lahti, Finland, June 8–11, 1992. p. 272–275. Rinne, M., Hellämäki, M., Nousiainen, J., Aura, E. & Huh- tanen, P. 1999b. Development of timothy during pro- gressing growth and subsequent nutritional implica- tions. Proceedings of the 12th International Silage Conference, Uppsala, Sweden, July 5–7, 1999. p. 166–167. – , Jaakkola, S. & Huhtanen, P. 1997. Grass maturity effects on cattle fed silage-based diets. 1. Organic matter digestion, rumen fermentation and nitrogen utilization. Animal Feed Science Technology 67: 1– 17. – , Jaakkola, S., Kaustell, K., Heikkilä, T. & Huhtanen, P. 1999a. Silages harvested at different stages of grass growth v. concentrate foods as energy and pro- tein sources in milk production. Animal Science 69: 251–263. – , Nykänen, A. & Ahvenjärvi, S. 1996. Maturity effects on botanical, morphological and chemical composi- tion of organically grown leys. In: Parente, G. et al. (eds.). Grassland and Land Use Systems. Proceed- ings of the 16th General Meeting of European Grass- land Federation, Grado (Gorizia), Italy, September 15–19, 1996. p. 575–578. Robertson, J.B. & Van Soest, P.J. 1981. The detergent system of analysis and its application to human foods. In: James, W.D.T. & Theander, O. (eds.). The analy- ses of dietary fibre in foods. New York: Marcell- Dekker. p. 123–158. Salo, M.-L. 1978. Kasvuasteen ja typpilannoituksen vaikutus säilörehunurmen rehuarvoon. Kehittyvä Maatalous 38: 3–10. – , Nykänen, A. & Sormunen, R. 1975. Composition, pepsin-HCl solubility and in vitro digestibility of for- ages at different growth stages. Journal of the Sci- entific Agricultural Society of Finland 47: 480–490. Sanderson, M.A. & Wedin, W.F. 1989. Phenological stage and herbage quality relationships in temperate grass- es and legumes. Agronomy Journal 81: 864–869. Shingfield, K.J., Jaakkola, S. & Huhtanen, P. 1999. Com- parison of the effects of dietary nitrogen supplements on the intake and milk production of Finnish Ayrshire dairy cows fed grass silage-based diets. Proceed- ings of the 12th International Silage Conference, Uppsala, Sweden, July 5–7, 1999. p. 159–160. Smith, L.W., Goering, H.K. & Gordon, C.H. 1972. Rela- tionships of forage composition with rates of cell wall digestion and indigestibility of cell walls. Journal of Dairy Science 55: 1140–1147. Syrjälä, L. & Ojala, R. 1978. Kevät- ja syyssadosta eri kehitysasteilla valmistetun timoteisäilörehun ravin- toarvo. Kehittyvä Maatalous 39: 36–49. Terry, R.A. & Tilley, J.M.A. 1964. The digestibility of the leaves and stems of perennial ryegrass, cocksfoot, timothy, tall fescue, lucerne and sainfoin, as meas- ured by an in vitro procedure. Journal of the British Grassland Society 19: 363–372. Theodorou, M.K., Williams, B.A., Dhanoa, M.S., McAl- lan, A.B. & France, J. 1994. A simple gas production method using a pressure transducer to determine the fermentation kinetics of ruminant feeds. Animal Feed Science and Technology 48: 185–197. Thomas, C., Aston, K. & Daley, S.R. 1985. Milk produc- tion from silage. 3. A comparison of red clover with grass silage. Animal Production 41: 23–31. Tuori, M., Kaustell, K., Valaja, J., Aimonen, E., Saaris- alo, E. & Huhtanen, P. 1996. Rehutaulukot ja ruokin- tasuositukset (Feed tables and feeding recommen- dations, in Finnish). 2nd ed. Yliopistopaino, Helsin- ki. 99 p. + 3 encl. Van Soest, P.J. 1994. Nutritional ecology of the ruminant. 2nd ed. Cornell University Press, Ithaca, NY. 476 p. 134 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 I N F I N L A N D Rinne, M. & Nykänen, A. Effects of harvesting strategy on organically grown leys SELOSTUS Ensimmäisen sadon korjuuaika vaikuttaa timotein ja puna-apilan seosnurmen satoon ja rehuarvoon Marketta Rinne ja Arja Nykänen Maatalouden tutkimuskeskus Kasvuajan jakamisen vaikutuksia ensimmäisen ja toi- sen sadon kesken tutkittiin Juvalla kahtena vuonna luonnonmukaisesti viljeltyyn seosnurmeen, jonka pää- kasvilajeja olivat timotei ja puna-apila. Ensimmäinen sato korjattiin kolmena eri aikana ja jälkikasvu sama- na päivänä elokuun lopussa. Kuiva-ainesato kasvoi en- simmäisessä sadossa 116 kg/ha päivässä, kun korjuu- ta siirrettiin myöhäisemmäksi, mutta vastakkainen ke- hitys jälkikasvussa korvasi sen osittain. Korjuuaika ei vaikuttanut eri satojen kasvilajikoostumukseen, mut- ta puna-apilan osuus oli huomattavasti pienempi en- simmäisessä sadossa (28 %) toiseen satoon verrattu- na (71 %). Koko kesän painotetussa nurmisadossa puna-apilan osuus pieneni 46:sta 35 %:iin, kun ensim- mäisen sadon korjuuta siirrettiin myöhäisemmäksi. Sekä timotein että puna-apilan ravitsemuksellinen arvo huononi ensimmäisen sadon kasvun edetessä, mutta timotei huononi nopeammin kuin puna-apila. Sulavan orgaanisen aineen pitoisuus kuiva-aineessa pieneni timoteissä 5,6 g/kg ja puna-apilassa 2,6 g/kg päivässä. Muutokset jälkikasvussa olivat vastakkai- sia. Ensimmäisen sadon kehityslinjat näkyivät kuiten- kin selvästi myös koko kesän painotetussa sadossa, koska ensimmäisen sadon osuus koko sadosta oli kes- kimäärin 68 % ja ensimmäisen sadon laatu vaihteli enemmän kuin toisen sadon. Tehoisan lämpösumman yhteys nurmikasvien D-arvoon alkukesällä oli selvä, joten lämpösumman hyödyntäminen nurmen korjuu- ajan valinnassa vaikuttaa mahdolliselta. Title Introduction Material and methods Results Discussion Conclusions References SELOSTUS