Agricultural and Food Science in Finland 285 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. 8 (1999): 285–298. The effect of incorporation time of different crops on the residual effect on spring cereals Hannu Känkänen Agricultural Research Centre of Finland, Plant Production Research, FIN-31600 Jokioinen, Finland, e-mail: hannu.kankanen@mtt.fi Arjo Kangas Agricultural Research Centre of Finland, South Ostrobothnia Research Station, FIN-61400 Ylistaro, Finland Timo Mela Agricultural Research Centre of Finland, Plant Production Research, FIN-31600 Jokioinen, Finland Unto Nikunen Agricultural Research Centre of Finland, North Ostrobothnia Research Station, Toholampi, FIN-69310 Laitala, Finland Hannu Tuuri Agricultural Research Centre of Finland, Data and Information Services, FIN-31600 Jokioinen, Finland Martti Vuorinen Agricultural Research Centre of Finland, Häme Research Station, FIN-36600 Pälkäne, Finland The effect of the time of incorporation of different green manures and barley residues on the grain yield of spring cereals in two successive seasons was studied in seven field trials. Annual hairy vetch (Vicia villosa Roth), red clover (Trifolium pratense L.), westerwold ryegrass (Lolium multiflorum Lam. var. westerwoldicum) and straw of spring barley (Hordeum vulgare L.) were incorporated into the soil by ploughing in early September, late October and the following May, and by reduced tillage in May. Spring barley was established in the following spring, and spring oats (Avena sativa L.) one year later. In general the grain yield of spring barley after legumes was similar to that after barley, in spite of the fact that N fertilization was reduced by 40 kg ha-1. The two autumn ploughing treatments resulted in a good yield of spring barley more reliably than did the spring incorporations. Because delayed autumn ploughing did not decrease the grain yield, a delaying procedure can be recommended for its potential of decreasing nitrogen leaching. Spring ploughing could be used on all but clay soils. Incor- porating ryegrass or red clover in spring by using reduced tillage often decreased the grain yield of barley. Timing of incorporation did not have a consistent effect on the grain yield of oats in the third experimental year. Key words: Avena sativa, decomposition, green manures, Hordeum vulgare, legumes, Lolium multi- florum, mineralization, mulching, Trifolium pratense, Vicia villosa © Agricultural and Food Science in Finland Manuscript received January 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. 8 (1999): 285–298. mailto:hannu.kankanen@mtt.fi 286 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 Känkänen, H. et al. Timing of plant biomass incorporation: effect on cereal grain yield Introduction The residual effect of a green manure crop is highly dependent on the species grown (Wall- gren and Lindén 1991). Legumes are generally considered to leave high amounts of N for the succeeding crop (Badaruddin and Meyer 1990), although there are great differences between leg- ume crops in this respect (Kirchmann and Marstorp 1991). In Finland, cool late autumn weather and cold winter can decrease the decom- position rate of plant material and nitrification of nitrogenous compounds in soil (Anderson 1960). However, mineralization processes has been found to occur at low temperatures, too (Müller and Sundman 1988, Van Schöll et al. 1997). On the basis of experiments with several dif- ferent green fallow crops, delayed ploughing in autumn was proposed mainly because of the re- duced risk of N leaching (Känkänen 1993), which is in accordance with several other results (Haynes 1994). However, the measures needed to support good utilization of the green manure N by spring-sown crops in Finland are not fully understood. Delayed incorporation of green ma- nure crops can be used to enhance synchroniza- tion of the release of N with the requirements of the succeeding crop. Incorporation of green ma- nure crop in spring, immediately before the next crop is sown, may lead to too late N mineraliza- tion with respect to the need of the succeeding crop (Thorup-Kristensen 1996). Delaying incor- poration of green manure crop in autumn can also affect the yield of the following crop: Sander- son and MacLeod (1994) found that potato plant- ed in spring following lupin incorporated on 1 October had a higher tuber yield than did that following lupin incorporated on 1 September. The method of incorporation of the crop res- idues can also affect the successive cereal grain yield, either because the N release from the in- corporated plant material differs or there are oth- er factors in the soil influencing yield, or both. Maillard and Vez (1991) noticed that cereal yield was higher when green manure was incorporat- ed lightly into the soil rather than by regular ploughing into the 20–25 cm soil layer. Direct drilling of grain sorghum into clover surface mulch was not recommended by Lemon et al. (1990), because N availability was not synchro- nous with the needs of the succeeding plant. The positive effect of N rich plant biomass on the succeeding cereal grain yield is often re- duced with increasing N fertilization (Badarud- din and Meyer 1990, Lindén and Wallgren 1993). Further, Francis and Knight (1993) state that af- ter different tillage methods, differences in yields can be compensated with different amount of fertilizer N. The aim of the study was to investigate how the time of incorporation (early or late autumn ploughing, and spring incorporation by plough- ing) of crops with different N content (hairy vetch, red clover and westerwold ryegrass, and straw of spring barley) affect the grain yield of the following spring cereal crop. Reduced till- age was added as an additional treatment as this practise is increasingly common in cereal crop- ping in Finland. The effects of different N ferti- lization rates of the following crop on the dif- ferences between the effects of other treatments was studied, too. Material and methods Hairy vetch (Vicia villosa Roth), red clover (Tri- folium pratense L.), westerwold ryegrass (Lo- lium multiflorum Lam. var. westerwoldicum) and straw residues of spring barley (Hordeum vul- gare L.) were incorporated into the soil by ploughing in early autumn (beginning of Sep- tember), late autumn (end of October) and spring (May) and by reduced tillage in spring. Incor- poration times were determined according to normal practices in cereal farming in Finland, autumn ploughing period starting after crop har- vest and ending when soil is frozen or too wet for ploughing. Time of spring tillage was deter- mined according to soil moisture suitable for 287 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. 8 (1999): 285–298. sowing. The experimental sites, design, treat- ments and samplings are described in detail by Känkänen et al. (1998). Spring barley and oats (Avena sativa L.) were harvested with a com- bine harvester when ripe (1.5 m x 7 m per plot). After the grains had been dried in an air stream (+40°C) and sorted, the grain yield was meas- ured and calculated as kg ha-1 at 15% moisture. Information on weather conditions during the e x p e r i m e n t a l y e a r s i s g i v e n i n d e t a i l b y Känkänen et al. (1998), and in Table 1. The names of the trials are abbreviated as follows: Jokioinen 1991–1993 = J1, Jokioinen 1993–1995 = J2, Pälkäne 1991–1993 = P1, Pälkäne 1993–1995 = P2, Ylistaro 1991–1993 = Y1, Ylistaro 1993–1995 = Y2 and Toholampi 1991–1993 = T. The crop of the first experimen- tal year (green manures and spring barley) is called precrop, the crop of the second experi- mental year (spring barley) is called 1st year test crop, and the crop of the third experimental year (oats) is called 2nd year test crop. Statistical methods The data from the seven different field trials were analysed separately. The main effects of precrop, incorporation treatment and N fertilization, and their interactions, on the grain yield of 1st year test crop (spring barley) were tested statistically by analysis of variance according to the split- split-plot design. Replication was considered a random effect, whereas precrop, incorporation treatment and N fertilization were considered fixed effects. Precrop was analysed as a main plot factor, incorporation treatment as a subplot factor and N fertilization as a sub-subplot fac- tor. If significant interaction between N fertili- zation and other treatments were found, the dif- ferences of the effect of N fertilization in differ- ent treatment combinations were examined, else significant effects of the precrop and incorpora- tion treatment and their interactions were exam- ined over all N fertilization levels. If an interac- tion between the precrop and incorporation treat- ment was found, the effects of incorporation treatments were determined separately for dif- ferent precrops. The differences were examined in pairs, and the means were compared by t-type contrast examinations. When there was no in- teraction, but the main effect was due to the pre- crop or incorporation treatment, the paired com- parisons were made by Tukey’s honest signicant difference (HSD) methods. Before the analysis of variance was per- formed, the consistency of different examina- tions with the assumptions of equality of group variances were checked by Box-Cox diagnostic plots. In addition the normality assumption of errors was assessed by graphic methods. All anal- yses were performed by means of the SAS sta- tistical package. MIXED (SAS 1992), UNIVAR- IATE (SAS 1990) and GPLOT (SAS 1991) pro- cedures were used. Results Precrop yields The dry matter yields of green manure crops varied, depending on site, year, species and sam- pling date (Table 2). In autumn, we measured 5000–8000 kg ha-1 dry matter of hairy vetch. However, in the succeeding spring the detecta- ble amount of dry matter in material left on the soil surface was only 2000–6000 kg ha-1. In red clover (total dry matter ranging from 1800 to 9500 kg ha-1), this was found at both Jokioinen and Toholampi in 1991–1992. A great propor- tion (as an average 50%) of the red clover dry matter was in roots, and the amount in red clo- ver grown annually increased sharply between samplings before early (12–38%) and late au- tumn (49–65%) ploughing. In contrast, the dry matter yield of vetch was mainly in above- ground plant biomass. The dry matter yield of westerwold ryegrass ranged from 2500 to 7000 kg ha-1. The average N content of the above- ground plant biomass varied between trials from 288 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 Känkänen, H. et al. Timing of plant biomass incorporation: effect on cereal grain yield Table 1. Weather conditions at the experimental sites in experimental years (data provided by the Finnish Meteorological Institute) and in 1961–1990 (Finnish Meteorological Institute 1991). Mean air temperature, °C Precipitation, mm 1991 1992 1993 1994 1995 1961– 1991 1992 1993 1994 1995 1961– 1990 1990 Jokioinen January –3.6 –2,1 2.3 –4.8 –3.6 –7.5 69 50 56 52 46 36 February –7.5 –2.7 –3.4 –13.9 –1.0 –7.4 16 31 16 1 58 24 March –1.0 0.4 –0.9 –3.2 –0.3 3.5 31 43 29 54 45 25 April 3.4 1.3 3.3 5.0 2.7 2.4 14 48 29 33 47 32 May 7.2 11.4 13.5 7.8 8.7 9.4 29 7 1 34 87 35 June 12.1 15.6 11.4 12.1 16.7 14.3 69 25 56 66 121 47 July 16.6 16.0 15.6 19.0 15.3 15.8 55 47 107 1 53 80 August 16.2 14.3 12.9 15.1 15.1 14.2 92 107 136 54 65 83 September 9.1 11.2 5.7 10.0 10.3 9.4 80 59 13 105 45 65 October 5.4 –0.6 3.0 4.4 7.6 4.7 49 64 51 75 66 58 November 2.6 –1.8 –3.6 –1.0 –2.8 –0.4 81 63 3 24 47 55 December –1.6 0.1 –3.4 –0.4 –8.5 –4.9 34 33 61 51 19 42 Year 4.9 5.3 4.3 4.2 5.0 3.9 619 577 558 551 698 582 Pälkäne January –4.6 –2.9 –2.8 –5.8 –4.0 –8.2 40 37 41 50 52 36 February –8.2 –3.1 –3.4 –14.6 –1.5 –8.0 13 39 16 2 58 25 March –1.4 0.3 –0.9 –3.2 –0.4 –3.6 33 47 31 54 36 27 April 3.4 0.6 2.6 4.5 2.1 2.2 17 56 25 43 26 32 May 7.5 11.5 13.3 7.9 8.8 9.5 22 8 3 48 65 37 June 12.8 16.2 11.6 12.7 17.0 14.7 88 30 46 75 76 50 July 17.3 15.8 15.7 19.2 15.6 16.3 41 58 75 5 37 74 August 16.6 14.1 13.1 15.5 15.5 14.6 103 136 128 75 60 82 September 9.5 11.5 5.9 10.3 10.5 9.7 68 105 18 84 33 64 October 5.5 –0.6 3.0 4.3 7.5 4.7 36 67 59 75 51 58 November 2.5 –2.7 –4.0 –1.4 –2.9 –0.7 65 61 5 35 48 50 December –2.1 –0.3 –4.0 –1.0 –9.5 –5.4 44 25 53 38 26 40 Year 4.9 5.0 4.2 4.0 4.9 3.8 570 669 501 583 568 574 Ylistaro January –4.1 –2.9 –3.0 –6.7 –3.8 –8.6 25 43 40 25 19 31 February –8.9 –2.6 –3.8 –13.8 –2.3 –8.4 14 31 14 1 39 21 March –1.7 0.6 –0.8 –3.6 –0.1 –4.1 39 36 17 38 52 23 April 3.9 0.2 3.1 4.2 2.1 2.0 12 23 23 26 22 29 May 6.5 10.9 11.6 6.8 7.7 8.8 56 13 16 7 44 38 June 12.3 15.1 10.9 12.5 16.1 14.0 147 18 84 81 75 42 July 16.4 14.5 15.2 17.8 14.9 15.5 26 77 86 28 45 68 August 15.7 13.2 12.6 14.4 14.1 13.6 60 103 122 52 34 70 September 7.9 10.4 5.4 9.1 9.6 8.8 88 91 26 56 48 61 October 5.2 –2.6 2.5 3.1 6.8 4.1 38 62 78 83 42 50 November 2.2 –3.7 –3.1 –2.0 –3.7 –1.4 49 47 10 31 25 45 December –2.0 0.2 –5.1 –0.8 –9.8 –6.2 25 41 51 25 12 35 Year 4.5 4.4 3.8 3.4 4.3 3.2 578 584 568 452 458 513 Toholampi January –6.4 –4.1 –4.4 –10.5 32 55 62 35 February –9.1 –4.6 –4.5 –10.0 18 29 20 24 March –4.3 –1.8 –1.7 –5.3 34 51 27 28 April 2.6 1.9 2.0 0.9 24 12 26 30 May 5.5 10.0 10.8 8.1 38 10 20 38 June 11.6 10.2 10.4 13.4 108 15 17 49 July 15.6 15.2 15.8 15.4 35 138 70 67 August 14.8 12.2 12.5 13.1 61 107 82 79 September 6.9 9.6 4.7 7.8 110 99 34 59 October 4.1 –3.2 1.6 2.8 46 47 99 49 November 1.1 –5.0 –3.6 –2.9 65 75 7 48 December –3.6 –0.6 –5.7 –7.9 33 48 76 38 Year 3.2 3.3 3.2 2.1 604 686 540 544 289 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. 8 (1999): 285–298. 2.1 to 3.1%, 1.2 to 3.4%, 0.9 to 1.8% and 0.8 to 1.4% in vetch, red clover, ryegrass and barley straw, respectively. The respevtive root N con- tent ranged from 1.5 to 3.0%, 1.3 to 2.8%, 0.8 to 1.7% and 1.1 to 1.9%. Total N yield ranged from 45 to 240, 40 to 220 and 25 to 90 kg ha-1 in vetch, red clover and ryegrass, respectively. The amount of N in plant biomass is more closely presented in our earlier article (Känkänen et al. 1998). The amount of incorporated barley straw was determined only in two trials: the total N yield in autumn was 90 kg ha-1 in P1 and 50 kg ha-1 in T. Grain yield of 1st year test crop The grain yield of the 1st year test crop (spring barley) differed markedly at the experimental sites. The lowest (J1) and highest (Y1) average grain yield varied from 500 to 5100 kg ha-1. Un- less otherwise mentioned, the differences be- tween treatments are statistically significant at the level P < 0.05 (Table 3). Grain yields pre- sented below are calculated as the means over N fertilization levels, because N fertilization nor- mally increased the grain yield in spite of other treatments. The few exceptions showing signif- icant interaction are examined more closely lat- er in the text. The precrop affected the grain yield of the 1st year test crop in four trials (P1, P2, Y2, T); the poor grain yield after red clover in three of these trials was partly caused by decreased N fertilization. The incorporation treatment affect- ed the grain yield of 1st year test crop in all tri- als except Y2. However, in trials P2, Y1 and T the effect of incorporation depended on the pre- crop. Table 2. Above-ground and root dry matter yield (kg ha-1) and N content (%, in parentheses) of green manure crops. J1 = Jokioinen 1991–1993, J2 = Jokioinen 1993–1995, P1 = Pälkäne 1991–1993, T = Toholampi 1991–1993. Above-ground dry matter Root dry matter (0–20 cm) Hairy Red Westerwold Hairy Red Westerwold vetch clover ryegrass vetch clover ryegrass J1 Early autumn 6910 (3.1) 5280 (3.0) 4380 (0.9) 240 (1.5) 1960 (2.0) 880 (0.7) Late autumn 7510 (3.1) 3510 (2.4) 3900 (1.2) 220 (1.9) 6030 (2.2) 1090 (0.9) Spring 1850 (2.2) 1160 (3.0) 1950 (1.1) 280 (2.2) 660 (3.0) 680 (1.2) Reduced tillage 2170 (2.3) 1180 (2.7) 2110 (0.9) 200 (2.6) 1770 (3.1) 1250 (0.8) J2 Early autumn 6170 (3.2) 2560 (3.2) 3160 (1.7) 710 (3.3) 1550 (2.4) 2150 (1.2) Late autumn 4670 (4.0) 3410 (3.4) 3610 (1.9) 810 (2.4) 3240 (2.7) 1290 (1.4) Spring 2000 (3.0) 2790 (3.4) 1810 (1.7) 250 (2.2) 2480 (3.0) 1310 (1.1) Reduced tillage 3970 (2.7) 2080 (3.3) 2100 (1.8) 720 (2.0) 2210 (3.2) 1620 (1.0) P1 Early autumn 6330 (3.0) 2280 (2.0) 2760 (0.9) 780 (1.6) 1410 (1.0) 2730 (0.8) Late autumn 6730 (2.9) 2650 (2.0) 2520 (1.0) 2110 (1.4) 4820 (1.6) 3110 (0.7) Spring 3320 (2.5) 2720 (2.1) 3760 (0.8) 2250 ( – ) 3650 ( – ) 3200 ( – ) Reduced tillage 4750 (2.4) 2290 (2.1) 3180 ((0.7) 1890 ( – ) 4750 ( – ) 3000 ( – ) T Early autumn 4490 (2.7) 2210 (1.6) 5390 (0.8) 240 (1.8) 290 (1.5) 750 (1.1) Late autumn 4610 (3.3) 1750 (2.1) 1150 (1.0) 940 (1.2) 1520 (1.6) 1440 (1.1) Spring 1800 (2.7) 710 (2.2) 1130 (1.3) 390 (1.5) 1860 (1.5) 2050 (1.4) Reduced tillage 1680 (2.7) 900 (2.5) 1350 (1.2) 340 (1.5) 1720 (1.6) 2960 (1.1) 290 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 Känkänen, H. et al. Timing of plant biomass incorporation: effect on cereal grain yield Table 3. Statistical significances of the main effects of the treatments and their interactions on grain yield of 1st year test crop (spring barley) and 2nd year test crop (oats). Degrees of freedom of F test are in subscript after treatments. J1 = Jokioinen 1991–1993, J2 = Jokioinen 1993–1995, P1 = Pälkäne 1991–1993, P2 = Pälkäne1993–1995, Y1 = Ylistaro 1991–1993, Y2 = Ylistaro 1993–1995, T = Toholampi 1991–1993. J1 J2 P1 P2 Y1 Y2 T 1st year test crop Precrop 3, 6 0.89 0.56 0.03 < 0.001 0.45 0.027 0.009 Incorporation 3, 24 < 0.001 0.046 0.003 < 0.001 0.17 0.29 < 0.001 Precrop x incorporation 9, 24 0.71 0.9 0.52 0.002 0.027 0.85 0.033 N fertilization 2, 64 0.007 < 0.001 < 0.001 < 0.001 < 0.001 <0.001 < 0.001 Precrop x fertilization 6, 64 0.26 0.11 0.48 < 0.001 0.46 0.17 0.052 Incorp. x fertilization 6, 64 0.47 0.57 0.52 0.012 0.39 0.77 0.16 Precr. x incorp. x fertil. 18, 64 0.38 0.88 0.28 0.95 0.63 0.69 0.033 2nd year test crop Precrop 3, 6 0.83 0.98 0.057 0.17 0.39 0.91 0.63 Incorporation 3, 24 0.11 0.39 0.14 0.33 0.052 0.11 0.003 Precrop x incorporation 9, 24 0.24 0.29 0.22 0.44 0.15 0.73 0.11 N fertilization 2, 64 0.024 0.003 0.58 0.65 0.26 0.96 0.16 Precrop x fertilization 6, 64 0.74 0.006 0.18 0.68 0.65 0.46 0.55 Incorp. x fertilization 6, 64 0.58 0.59 0.2 0.21 0.35 0.95 0.014 Precr. x incorp. x fertil. 18, 64 0.31 0.95 0.021 0.37 0.42 0.71 0.27 Effect of precrop The grain yield of the 1st year test crop showed that hairy vetch had the expected 40 kg ha-1 N effect; in one trial (P1), this effect was even higher (Fig. 1). Although the increase in the yield of 1st year test crop after vetch was high compared with that after barley in J2, 1100 kg ha-1, the effect of the precrop was not statistically significant. The differences between the grain yields of 1st year test crop after red clover and barley were small in three trials (J1, P1, Y1) in spite of 40 kg ha-1 lower N fertilization after red clover (Fig. 1, Table 4). In three trials (P2, Y2, T), the grain yield of 1st year test crop was lower after red clover than after barley. In these trials also N yield of red clover was lower than in other tri- als, above ground N yield being 20–30 kg ha-1 in the former trials and 50–90 kg ha-1 in the latter. However, in trials P2 and T the differences be- tween precrops varied, depending on the incor- poration treatment (Table 4). The average grain yield of 1st year test crop after the 90 kg N ha-1 above ground yield of red clover in J2 was more than 200 kg ha-1 higher than that of after barley; the difference was not statistically significant, however. In one trial (P2), the average grain yield of 1st year test crop was clearly smaller after west- erwold ryegrass than after barley, although the difference varied depending on the incorpora- tion treatment. The average grain yield of 1st year test crop was, however, 500 kg ha-1 higher after westerwold ryegrass than after barley in three trials (J2, Y1, T). The differences were not statistically significant. Effect of incorporation treatment According to the grain yield of 1st year test crop, both ploughing dates in autumn were suitable at all experimental sites after all precrops (Fig. 2, Table 4), except in Y1, in which late autumn ploughing of westerwold ryegrass decreased the grain yield of 1st year test crop by an average of 550–840 kg ha-1 as compared with the other in- corporation treatments. After hairy vetch and barley a similar tendency was seen, but the dif- ference (on average 300 kg ha-1) was not statis- tically significant (Table 4). 291 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. 8 (1999): 285–298. 0 1000 2000 3000 4000 5000 6000 J1 J2 P1 Y2 Hairy vetch (-40 N) Red clover (-40 N) Westerwold ryegrass Spring barley b a a a a b ab ab Fig. 1. The main effect of the precrop on grain yield of 1st year test crop (spring barley) in trials with no interactions between incorporation and precrop. The bars are based on means of all incorporation and N fertilization treatments, reduced by 40 kg ha-1 after legumes (standard error of means, SEM: J1 = 41, J2 = 558, P1 = 352, Y2 = 187 kg ha-1). Within trials, yields followed by the same letter are not statistical- ly different at level P<0.05. There was a statistically significant interaction between precrop and incorporation treatment in trial P2, Y1 and T; results presented in Table 4. J1 = Jokioinen 1991–1993, J2 = Jokioinen 1993–1995, P1 = Pälkäne 1991–1993, P2 = Pälkäne 1993–1995, Y1 = Ylistaro 1991–1993, Y2 = Ylistaro 1993–1995, T = Toholampi 1991–1993. 0 1000 2000 3000 4000 5000 6000 J1 J2 P1 Y2 Ploughing, early autumn Ploughing, late autumn Ploughing, spring Reduced tillage, spring a b b b a b b ab a b b b Fig. 2. The main effect of incorporation treatment on grain yield of 1st year test crop (spring barley) in trials with no interactions between incorporation and precrop. The bars are based on means of all precrops and N fertilization treatments, reduced by 40 kg ha-1 after legumes (standard error of means, SEM: J1 = 41, J2 = 291, P1 = 348, Y2 = 184 kg ha-1). Within trials, yields followed by the same letter are not statistical- ly different at level P<0.05. There was a statistically significant interaction between precrop and incorporation treatment in trial P2, Y1 and T; results presented in Table 4. J1 = Jokioinen 1991–1993, J2 = Jokioinen 1993–1995, P1 = Pälkäne 1991–1993, P2 = Pälkäne 1993–1995, Y1 = Ylistaro 1991–1993, Y2 = Ylistaro 1993–1995, T = Toholampi 1991–1993. 292 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 Känkänen, H. et al. Timing of plant biomass incorporation: effect on cereal grain yield Table 4. Effect of incorporation treatment of different precrops on the succeeding 1st year test crop (spring barley) grain yield (kg ha-1) in trials with interactions between incorporation and precrop. The figures are means of N fertilization treatments, reduced by 40 kg ha-1 after legumes. The main effect of precrop and incorporation is presented in ‘average’ columns and rows. P2 = Pälkäne 1993–1995, Y1 = Ylistaro 1991– 1993, T = Toholampi 1991–1993. Hairy Red Westerwold Spring vetch clover ryegrass barley Average P2 (SEM 130) (SEM 65) Early autumn 3100ab 2210b 2550c 2940b 2700b Late autumn 3280b 2170b 2460bc 2610a 2630b Spring 2970a 1770a 2200ab 2790ab 2430a Reduced tillage 3100ab 1550a 1960a 2950b 2390a Average (SEM 137) 3110g 1920f 2290f 2820g Y1 (SEM 434) (SEM 324) Early autumn 4920a 4850b 5550b 5130a 5110 Late autumn 4850a 5150b 5000a 4670a 4920 Spring 5270a 4960b 5650b 4970a 5210 Reduced tillage 5100a 4340a 5840b 5130a 5100 Average (SEM 405) 5030 4830 5510 4980 T (SEM 225) (SEM 144) Early autumn 5080b 3930b 4830ab 4760b 4650b Late autumn 4640b 4290b 4840ab 4650b 4600b Spring 4950b 4420b 5090b 4400b 4710b Reduced tillage 3730a 2710a 4410a 3650a 3630a Average (SEM 165) 4600g 3840f 4790g 4360fg Within columns, means followed by the same letter are not statistically different at level “P<0.05; the italic rows (Average) are excluded from this comparison. Within italic rows,” means followed by the same letter are not statistically different at level P<0.05 (P2, T). Standard error of means (SEM) is presented for each comparison. Ploughing in spring was not an advantageous on clay soil at Jokioinen (J1, J2), the grain yield of 1st year test crop being 250–550 ka ha-1 lower than with autumn ploughing or reduced tillage in spring, irrespective of the precrop (Fig. 2). Even in P2 (sandy soil), incorporation of the green manure crops by ploughing in spring resulted in a smaller grain yield than did autumn ploughing (Table 4). In the other trials, the grain yield of 1st year test crop after spring ploughing was about the same as that after autumn ploughings. Although spring tillage with a cultivator was applicable on clay soil at Jokioinen, at other sites the grain yield of 1st year test crop was often smallest after reduced tillage in spring, especially after red clover. The grain yield of 1st year test crop was smallest after reduced tillage in spring in two trials irrespective of the precrop (P1, T), in two trials with red clover (P2, Y1) and in one trial (P2) with westerwold ryegrass as the pre- crop (Fig. 2, Table 4). In these cases, the differ- ence between reduced spring tillage and autumn ploughing treatments was marked, on average 750 kg ha-1. Effect of N fertilization N fertilization clearly increased the grain yield of 1st year test crop (Table 5). However, in P2, N fertilization did not increase the grain yield after hairy vetch (interaction between precrop and N fertilization, P < 0.001), and the yield in- crease was smaller after early autumn plough- 293 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. 8 (1999): 285–298. ing than after other incorporation treatments (in- teraction between incorporation and N fertiliza- tion, P = 0.012). In one trial (T), the yield-in- crease due to N fertilization after vetch and bar- ley was smaller whith spring ploughing than oth- er incorporation treatments (interaction between precrop, incorporation and N fertilization, P = 0.033). The same phenomenon was found after westerwold ryegrass when early autumn ploughing was used. Even so, the yield-increas- Table 5. Effect of precrop, incorporation and N fertilization on the 1st year test crop (spring barley) grain yield (kg ha-1). Standard errors of means (SEM) are presented in parentheses after abbreviation of each trial. J1 = Jokioinen 1991–1993, J2 = Jokioinen 1993–1995, P1 = Pälkäne 1991–1993, P2 = Pälkäne 1993–1995, Y1 = Ylistaro 1991–1993, Y2 = Ylistaro 1993–1995, T = Toholampi 1991–1993. Hairy vetch Red clover Westerwold ryegrass Spring barley 0N 40N 80N 0N 40N 80N 40N 80N 120N 40N 80N 120N J1 (SEM 88) Early autumn 590 530 650 550 610 600 650 620 740 570 790 700 Late autumn 550 590 740 700 740 640 580 640 720 560 620 540 Spring 110 70 90 150 70 120 50 70 40 100 160 160 Reduced tillage 660 790 720 620 650 620 360 620 710 620 650 760 J2 (SEM 638) Early autumn 4900 5380 6140 4270 4390 4650 4430 5340 4910 3720 4530 4090 Late autumn 4620 5260 5650 4190 4140 5240 4240 5050 5340 3950 4310 4530 Spring 4260 5260 5690 3970 4310 3880 3880 4630 4580 3820 4360 4030 Reduced tillage 4630 5200 6020 3840 4890 4360 4590 4840 5020 3710 4180 4460 P1 (SEM 512) Early autumn 3560 3390 5290 2650 2880 3000 3110 3460 3700 2840 3270 3090 Late autumn 3400 4090 4380 2210 3930 3230 2710 3400 3040 2620 3340 4060 Spring 3170 3870 4050 2390 3220 3760 2810 3680 3380 2340 3240 3160 Reduced tillage 2250 3460 3410 2290 2430 3900 1980 2420 2580 2320 2790 2620 P2 (SEM 187) Early autumn 3210 3030 3040 1970 2230 2420 2230 2700 2730 2620 3110 3100 Late autumn 3290 3340 3200 1720 2210 2580 2110 2560 2710 2070 2920 2840 Spring 2760 3100 3060 1340 1960 2010 1790 2380 2440 2350 3140 2900 Reduced tillage 2930 2900 3470 1200 1470 1970 1240 2220 2410 2310 3040 3490 Y1 (SEM 503) Early autumn 4580 4700 5480 4600 4740 5220 5260 5350 6040 4780 5050 5550 Late autumn 4360 4860 5310 4670 5030 5610 4520 5600 4880 4190 4490 5320 Spring 4450 5580 5790 3900 5470 5510 5240 5680 6030 4770 5000 5150 Reduced tillage 4240 5540 5500 3730 4160 5140 5490 6020 6010 4480 5050 5870 Y2 (SEM 260) Early autumn 4970 5110 4800 4470 4800 4770 4830 4780 4860 4550 5290 4990 Late autumn 4750 4850 4860 4080 4820 4670 4760 4830 4810 4860 5040 5130 Spring 4680 5220 4840 4450 4600 5080 4330 4730 5020 4890 5090 4940 Reduced tillage 4790 5060 4750 3990 4520 4700 4320 4740 4900 4550 5010 5240 T (SEM 281) Early autumn 3670 5240 6340 2300 4190 5300 4060 4840 5580 3550 5010 5730 Late autumn 2980 4770 6160 3260 4090 5510 3570 5010 5930 3230 4820 5890 Spring 4170 4770 5900 3110 4410 5730 3870 5330 6060 3290 4850 5040 Reduced tillage 2200 3970 5020 1690 2400 4050 3050 4570 5610 2390 3710 4830 294 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 Känkänen, H. et al. Timing of plant biomass incorporation: effect on cereal grain yield ing effect of N fertilization was clear in the above cases, too. Grain yield of 2nd year test crop Effect of precrop The precrop did not have a statistically signifi- cant effect on the grain yield of 2nd year test crop (oats), although in all trials except J1 the yield was somewhat smaller (in J2, P1 and Y1 on average 200 kg ha-1) after red clover than af- ter other precrops (Fig. 3). Effect of incorporation treatment The incorporation treatment had a statistically significant effect on the grain yield of 2nd year test crop in two trials, Y1 and T (Table 3). In these trials, the plots with reduced spring tillage in the preceding season increased the average grain yield of 2nd year test crop by 200–400 kg ha-1 as compared with other incorporation treat- ments (Fig. 4). Effect of N fertilization At Jokioinen (J1, J2), the lowest rate of N ferti- lization of 1st year test crop resulted in a small- Fig. 3. The main effect of the pre- crop on grain yield of 2nd year test crop (oats). The bars are based on means of treatments (standard er- ror of means, SEM: J1 = 366, J2 = 579, P1 = 168, P2 = 102, Y1 = 198, Y2 = 126, T = 149 kg ha-1). J1 = Jokioinen 1991–1993, J2 = Jokio- inen 1993–1995, P1 = Pälkäne 1991–1993, P2 = Pälkäne 1993– 1995, Y1 = Ylistaro 1991–1993, Y2 = Ylistaro 1993–1995, T = Toholampi 1991–1993. 0 2000 4000 6000 8000 J1 J2 P1 P2 Y1 Y2 T Hairy vetch Red clover Westerwold ryegrass Spring barley 0 2000 4000 6000 8000 10000 J1 J2 P1 P2 Y1 Y2 T Ploughing, early autumn Ploughing, late autumn Ploughing, spring Reduced tillage, spring a b ab ab Fig. 4. The main effect of incor- poration treatment after the pre- crop on grain yield of 2nd year test crop (oats). The bars are based on means of treatments (standard er- ror of means, SEM: J1 = 271, J2 = 399, P1 = 130, P2 = 87, Y1 = 189, Y2 = 117, T = 149 kg ha-1). With- in trials, yields followed by the same letter are not statistically dif- ferent at level P<0.05. J1 = Jokioinen 1991–1993, J2 = Jokioi- nen 1993–1995, P1 = Pälkäne 1991–1993, P2 = Pälkäne 1993– 1995, Y1 = Ylistaro 1991–1993, Y2 = Ylistaro 1993–1995, T = Toholampi 1991–1993. 295 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. 8 (1999): 285–298. er grain yield of 2nd year test crop than did the two higher N fertilization levels. In J1, the dif- ferences between the lowest level and the two higher fertilization levels were about 200 kg ha-1, irrespective of the other treatments. In J2, the differences varied considerably, depending on precrop (interaction between precrop and N fer- tilization, P = 0.006): the maximum difference was nearly 1000 kg ha-1 with barley as a precrop, whereas there were no differences when red clo- ver was the precrop. In other trials, N fertiliza- tion of 1st year test crop did not affect the grain yield of 2nd year test crop. In two other individ- ual cases, there was an interaction between N fertilization and other treatments (T: between incorporation and fertilization, P = 0.014; P1: between precrop, incorporation and fertilization, P = 0.021. Table 3). For these interactions we could not find any solid explanations. Discussion The ability of incorporated N-rich plant biomass to increase the succeeding cereal grain yield was expected, partly because N mineralized from the residues correlates positively with the crop N content (Vinther 1994, Clement et al. 1995), and partly because earlier results had suggested such an increase (Kauppila 1983, Känkänen 1993). The presumption of a 40 kg ha-1 residual N ef- fect after legumes was correct, although the ef- fect of hairy vetch as a precrop exceeded this figure in some trials. Also the effect of red clo- ver fell below the presumption, if the growth of clover was poor. The study of soil mineral N (Känkänen et. al 1998), showed that early autumn ploughing in- creased soil mineral N at the beginning of the following growing season as compared with oth- er incorporation times. Late autumn ploughing increased soil mineral N as compared with spring incorporation only when the soil mineral N con- tent was exceptionally high. Soil conditions suit- able for N mineralization after late autumn in- corporation was concluded to last generally too short time under Finnish conditions to result in substantial net N mineralization before spring. Thus the release of N from incorporated plant biomass during the following summer can be essential for the yield of the following crop, ac- cordingly to Francis et al. (1994), who found that grain yield of spring wheat correlated positively with net N mineralization during the growing season after crops with a different N content. Francis et al. (1994) also found that grain yield of spring wheat correlated positively with soil mineral N content before the growing sea- son. In the present study however, the yield could not be deduced from the soil N contents, as in general spring barley yields were similar after early and late autumn ploughing. Similar soil N but lower yields after spring incorporation in some cases when compared with late autumn ploughing confirms this conclusion. Tillage treatment obviously affected the other growing conditions so, that the effect of soil mineral N was masked. Because decreasing the risk of N leaching (Haynes 1994, Känkänen et al. 1998), delayed ploughing in autumn is preferable to early au- tumn ploughing for incorporating a green ma- nure crop. Delayed autumn ploughing is par- ticularly suitable for red clover sown in the spring of the green manure year, giving the clo- ver a longer time to accumulate N; Wivstad (1997) found that the N yield of red clover dou- bled between the ages of 14 and 20 weeks. In our study cereal yields were better after late ploughed red clover, even in Y1, in which late autumn ploughing otherwise decreased the grain yield of the following 1st year test crop (spring barley). Changes in mineralization rate of plant bio- mass are also marked due to changes in chemi- cal composition of the biomass during plant growth (Franzluebbers et. al 1994, Wivstad 1997). In our study, however, this effect was expected to be small as compared with the de- crease in mineralization due to lower soil tem- peratures in late autumn (Anderson 1960). Soil type and previous crop have to be taken 296 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 Känkänen, H. et al. Timing of plant biomass incorporation: effect on cereal grain yield into account when considering time of tillage. Generally spring ploughing is not recommend- ed for heavy clay soils (Mikkola 1989). On the other hand, reduced tillage with a cultivator in spring resulted in our study in comparable grain yield with autumn ploughing on heavy clay soil. However, mistiming either the basic tillage or seed bed preparation can lead to a major yield loss. On other soil types tested in our study, spring ploughing decreased the grain yield as compared with autumn ploughing in only one trial, whereas reduced tillage in spring reduced the yield in many cases. When comparing reduced tillage and plough- ing of green manure, Poutala and Hannukkala (1995) found that reduced tillage had an adverse effect on the following grain yield, but Maillard and Vez (1991) found a beneficial effect. In the former study autumn ploughing was compared with reduced tillage of hairy vetch and persian clover in both autumn and in spring in Finland, whereas the latter group compared shallow and deep autumn incorporation of mustard in Swit- zerland. According to the present study, the re- duced tillage of red clover, a perennial strongly competing with cereal crops by regrowth, is par- ticularly unsuitable. Even in the absence of com- petition, an adverse effect was obvious, reduced tillage in spring being an almost equally poor method for incorporating of both westerwold ryegrass and red clover. Although N fertilization of the following crop can compensate the differences caused by pre- crops (Lindén and Wallgren 1993) or tillage methods (Francis and Knight 1993), the effect of incorporation time was similar at all N ferti- lization rates in this study. Thus, timing of in- corporation of crop biomass do not depend on the fertilization intensity used in the farming system, but the decisive factor is the amount and content of N in the biomass. Because of the variable effects in individual trials during the second after-effect year, neither the timing nor the method of incorporation could be concluded to clearly affect the grain yield of 2nd year test crop, oats. The results suggest, that conventional early autumn ploughing is no more appropriate than any of the other tillage treat- ments used in this study. Because of numerous experimental sites and two experimental years, this study covered well the Finnish growing conditions. However, there was variation in results between individual tri- als caused by anomalous weather conditions. In our opinion this did not cause serious problems in interpretation of the results, even in J1 where the drought severely decreased the yield of spring barley. The main conclusions of this study can be generalized in conditions where soil is frozen during long winter period. Conclusions Our results suggest that autumn ploughing is a more reliable procedure than ploughing or re- duced tillage in spring, in efforts to obtain good spring cereal yields under Finnish conditions. Because of no adverse effect on the grain yield of the succeeding spring barley, autumn plough- ing should be delayed when incorporating N rich green manure crops. Also spring ploughing could be used on all but clay soils, although an adverse effect on the grain yield of spring barley was seen even on sandy soil in some cases. Reduced till- age is not recommended for incorporating grass- es or perennial legumes in spring. References Anderson, O.E. 1960. The effect of low temperatures on nitrification of ammonia in Cecil sandy loam. Soil Science Society of America Proceedings 24: 286– 289. Badaruddin, M. & Meyer, D.W. 1990. Green-manure leg- ume effects on soil nitrogen, grain yield, and nitro- gen nutrition of wheat. Crop Science 30: 819–825. Clement, A., Ladha, J.K. & Chalifour, F.P. 1995. Crop 297 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. 8 (1999): 285–298. residue effects on nitrogen mineralization, microbial biomass, and rice yield in submerged soils. Soil Sci- ence Society of America Journal 59: 1595–1603. Finnish Meteorological Institute 1991. Climatological sta- tistics in Finland 1961–1990. Supplement to the Me- teorological Yearbook of Finland 90, 1: 125 p. Francis, G.S., Haynes, R.J. & Williams, P.H. 1994. Nitro- gen mineralization, nitrate leaching and crop growth after ploughing-in leguminous and non-leguminous grain crop residues. Journal of Agricultural Science 123: 81–87. – & Knight, T.L. 1993. Long-term effects of conventional and no-tillage on selected soil properties and crop yields in Canterbury, New Zealand. Soil & Tillage Research 26: 193–210. Franzluebbers, K., Weaver, R.W. & Juo, A.S.R. 1994. Mineralization of labeled N from cowpea (Vigna un- guiculata L. Walp.) plant parts at two growth stages in sandy soil. Plant and Soil 160: 259–266. Haynes, R.J. 1994. Impact of management practices on nutrient cycling. In: Pankhurst, Doube, Gupta & Grace (eds.). Soil biota: management of sustainable farm- ing systems. p. 172–181. Känkänen, H. 1993. Nitrogen in soil and yields of cere- als after green fallows. Soil Tillage and Environment. Proceedings of NJF seminar no. 228, Jokioinen, Fin- land, 8–10 June 1993. p. 260–264. –, Kangas, A., Mela, T., Nikunen, U., Tuuri, H. & Vuori- nen, M. 1998. Timing incorporation of different green manure crops to minimize the risk of nitrogen leach- ing. Agricultural and Food Science in Finland 7: 553– 567. Kauppila, R. 1983. Palkokasvien käyttö viherlannoituk- sessa. Summary: Use of legumes in green manur- ing. In: Biologisen typensidonnan ja ravinnetypen hyväksikäytön projekti. 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Summary: Effects of autumn ploughing and different reduced tillage methods on yield and quali- ty of spring wheat 1975–1988. Vakolan tutkimus- selostus 54. p. 3–32. Müller, M.M. & Sundman, V. 1988. The fate of nitrogen (15N) released from different plant materials during decomposition under field conditions. Plant and Soil 105: 133–139. Poutala, R.T. & Hannukkala, A. 1995. The effect of the method of incorporation of Trifolium resupinatum L. and Vicia villosa Roth. residues in the soil and the performance of a succeeding cereal crop. Acta Agri- culturae Scandinavica, Sect. B, Soil and Plant Sci- ence 45: 251–257. Sanderson, J.B. & MacLeod J.A. 1994. Soil nitrate pro- file and response of potatoes to fertilizer N in rela- tion to time of incorporation of lupin (Lupinus albus). Canadian Journal of Soil Science 74, 2: 241–246. SAS Institute Inc. 1990. SAS Procedures Guide. Version 6, Third Edition, Cary, NC. 705 p. – 1991. SAS System for Statistical Graphics. 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Swedish Journal of Agricultural Research 21: 67–77. Wivstad, M. 1997. Plant morphology and content of ni- trogen, cell wall and lignin at different phenological stages of red clover and yellow sweetclover. Swed- ish Journal of Agricultural Research 27: 3–14. 298 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 Känkänen, H. et al. Timing of plant biomass incorporation: effect on cereal grain yield SELOSTUS Syyskyntö on luotettava tapa muokata kasvimassa maahan Hannu Känkänen, Arjo Kangas, Timo Mela, Unto Nikunen, Hannu Tuuri ja Martti Vuorinen Maatalouden tutkimuskeskus Huoli viherlannoitustypen kohtalosta maahan muok- kaamisen jälkeen synnytti tarpeen selvittää sopivin- ta muokkaamisen ajankohtaa. Vaikka maan typpimää- ritykset antavatkin käsityksen muokkausajankohdan suorasta vaikutuksesta huuhtoutumisriskiin, vasta seuraavat kasvukaudet täydentävät tiedon ajoituksen onnistumisesta. Pieni seuraavan kasvin sato lisää vä- lillisesti ravinteiden huuhtoutumisriskiä, koska ravin- teiden ottaminen maasta on vähäisempää suuren sa- don tuottavaan kasviin verrattuna. Kahdesta typen huuhtoutumisriskiä vähentävästä muokkausajankoh- dasta tulee viljelyn kannattavuuden vuoksi valita se, joka antaa paremman satovaikutuksen. Tutkimus perustuu viherkesantovaihtoehtoihin ta- vanomaisessa viljanviljelyssä. Aiempien tutkimustu- losten osoitettua viherlannoitteen muokkausajankoh- dan vaikuttavan typen huuhtoutumiseen ja hyväksi- käyttöön yleensä, haettiin tässä tutkimuksessa parhai- ta ajankohtia typpipitoisuuksiltaan erilaisten kasvus- tojen muokkaamiseen. Seitsemässä kokeessa Maatalouden tutkimuskes- kuksen neljällä tutkimusasemalla yksivuotisena viher- kesantona kasvaneet ruisvirna, puna-apila ja wester- woldin raiheinä sekä tuleentuneena korjatun ohran sänki ja puintijäte kynnettiin maahan joko aikaisin tai myöhään syksyllä (vaihdellen syyskuun alusta mar- raskuun alkuun) tai keväällä ennen kylvömuokkaus- ta. Kyntöjen vaihtoehtona kasvustot muokattiin maa- han myös kyntämättä keväällä ennen varsinaista kyl- vömuokkausta. Syyskynnöt johtivat hyvään seuraavaan ohrasatoon luotettavammin kuin kevätkyntö tai kevennetty muok- kaus keväällä. Kevätkyntöä voidaan kuitenkin käyttää typen huuhtoutumisen välttämiseksi lukuun ottamatta savimaita, joilla se selkeästi pienensi ohran jyväsatoa. Erityisesti raiheinän ja puna-apilan kevennetty muok- kaaminen maahan keväällä pienensi usein samana ke- väänä kylvetyn ohran jyväsatoa. Muokkauksen vaiku- tus kauran jyväsatoon toisena kasvukautena muok- kausten jälkeen vaihteli, eikä mitään muokkausmene- telmää voida sen perusteella pitää muita parempana. Aikaisemmin julkaistussa, maan mineraalitypen määriä selvittäneessä tutkimuksen osassa päädyttiin suosittelemaan kynnön viivyttämistä typen huuhtou- tumisen vähentämiseksi. Jyväsatojen perusteella syyskynnön viivyttäminen ei vaaranna viljelyn kan- nattavuutta. Lokakuun olosuhteita tulee kuitenkin seurata, jotta vältetään maan rakenteen vaurioittami- nen kyntämällä liian märissä oloissa. Kokeissa kas- vustolliset ruudut olivat syksyllä kynnettäessä sel- keästi kuivempia kuin sängellä olevat. Kun muok- kausajankohdan vaikutus maan mineraalitypen mää- rään oli lisäksi pieni viljan jälkeen ja kasvoi viher- kesannon typpipitoisuuden kasvaessa, kannattaa maa- tilan syyskynnöt aloittaa sängiltä ja päättää typpi- pitoisimpiin viherkesantoihin. Title Introduction Material and methods Results Discussion References SELOSTUS