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Effects of simplified cultivation on the growth and yield of spring barley on a sandy loam soil. 1. Shoot growth and grain yield; response to nitrogen
Soil & Tillage Research, 22 (1992) 159-171
159
Elsevier Science Publishers B.V., Amsterdam
Effects of simplified cultivation on the growth and yield of spring barley on a sandy loam soil. 1. Shoot growth and grain yield; response to nitrogen M.A. Braim ~, K. Chaney 2 and D.R. Hodgson Department of Pure and Applied Biology, University of Leeds, Leeds LS2 9JT, UK (Accepted 20 November 1990)
ABSTRACT Braim, M.A., Chaney, K. and Hodgson, D.R., 1992. Effects of simplified cultivation on the growth and yield of spring barley on a sandy loam soil. I. Shoot growth and grain yield; response to nitrogen. Soil Tillage Res., 22:159-17 I. Two experiments, each of three years duration ( 1975-1977 and 1978-1980), were carried out on a sandy loam soil to investigate the effects of mouldboard ploughing, shallow tine cultivation and direct drilling on the growth and yield of spring barley receiving different rates of application of nitrogenous fertilizer. Grain yields of the ploughed and shallow-cultivated treatments were similar ( ~ 6 t ha- ~) provided optimum amounts of nitrogenous fertilizer were applied, but direct drilling reduced yield, on average by 23% at 30-35 kg nitrogen (N) ha -~ and by 12% at 115-150 kg N ha -~. The direct cause of the reduction in grain yield after direct drilling compared with ploughing was a lower number of ears, except in 1977 when the difference was due to a smaller number of grains per ear and a lower thousand-grain weight. In the absence of nitrogenous fertilizer, less N was taken up by direct-driUed barley during its growth than by barley grown after ploughing or shallow tine cultivation, and there was still a difference at the highest level of fertilizer applied. The most profitable rates of N application were calculated for each cultivation system from fitted quadratic equations. These optimum rates were similar for all cultivation treatments in the final year of the first experiment ( ~ 120 kg N h a - l ), and were similar for direct drilling and ploughing in the second experiment ( ~ 130 kg N ha- ~), whereas the optimum for shallow cultivation was 185 kg N ha- i. At prevailing grain and fertilizer prices, the margin over fertilizer costs was between £73 and £87 ha- ~less from direct drilling than from ploughing or shallow tine cultivation.
INTRODUCTION In a comprehensive review, Cannell ( 1985 ) presented the results of many tillage experiments carried out in northwest Europe during the 1960s and Present addresses: ~Corpslanding, Hutton Cranswick, Driffield, N. Humberside, YO25 9QF, UK; 2Levington Agriculture Ltd., Ipswich, Suffolk, IP 10 0LU, UK.
© 1992 Elsevier Science Publishers B.V. All fights reserved 0167-1987/92/$05.00
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M.A. BRAIM ET AL.
1970s to compare direct drilling and other simplified cultivation systems with conventional mouldboard ploughing. On a wide variety of soil types, crops of direct-drilled winter wheat have given yields very similar to crops grown using conventional tillage. Spring barley, however, has given more variable results following direct drilling. In the UK, similar yields have been reported after direct drilling, shallow tillage and ploughing on clay loams (Ellis et al., 1977; Patterson et al., 1980; Clutterbuck and Hodgson, 1984), on a welldrained sandy loam (Elliott et al., 1977) and on a rendzina (Pollard et al., 1981 ). On a sandy clay loam, Chaney et al. (1985 ) reported that over a 10year period of continuous cropping with spring barley, mean grain yields were marginally lower after direct drilling than after shallow cultivation or ploughing. In Scotland, Holmes ( 1977 ), Pidgeon and Soane ( 1977 ), Pidgeon ( 1981 ) and O'Sullivan and Ball (1982), working on soils with impeded drainage, found that direct-drilled crops were lower yielding than those following ploughing. In The Netherlands, on a sandy soil, direct drilling and ploughing produced similar yields of spring barley (Bakermans and de Wit, 1970; Ten Holte, 1982), but in Belgium on a loess, Frankinet et al. (1979) reported a 15% reduction in yield after direct drilling. That yields of spring barley can be significantly greater after direct drilling than after ploughing was shown by Braim et al. (1984). This was due to a plough pan in the latter treatment causing transient waterlogging during an unusually wet spring. Mineral soils with a high proportion of coarse and fine sand are unstable structurally, easily become compacted and, because of the low content of colloidal material, natural fissures for the penetration of roots are few. These soils may not, therefore, be suitable for direct drilling of cereals, some soil disturbance being necessary for achieving satisfactory yields, particularly of spring-sown cereals. Two experiments, each of 3 years duration, were started on a sandy soil in Northern England, one in 1975 and the other in 1978, to compare direct drilling and shallow tine cultivation with mouldboard ploughing. The absence of cultivation reduces the uptake of nitrogen (N) by the crop (Hodgson et al., 1977; Clutterbuck and Hodgson, 1984), therefore each cultivation treatment received increasing rates of application of nitrogenous fertilizer so that the N factor might be eliminated from comparisons between tillage treatments. In this paper, results relating to yields, responses to N and N uptake by shoots of spring barley are presented. The effects of treatments on soil properties and root growth, with special reference to the efficiency of the root system and water use by the crop, are described in a second paper (Braim et al., 1991 ). Sharma ( 1985 ) reported results relating to 1976 only.
SIMPLIFIED CULTIVATION AND SPRING BARLEY. 1. SHOOTS
161
MATERIALSAND METHODS The experiments were conducted on two field sites at Askham Bryan College of Agriculture and Horticulture, near York, North Yorkshire. The soil of both sites is a stagnogleyic argillic brown earth classified by the Soil Survey of England and Wales as the Wighill series ( C r o m p t o n and Matthews, 1970 ). A sandy loam with sandstone cobbles and pebbles merges into a sandy clay loam at ~ 45 cm; structure at the surface is weak, becoming coarse subangular blocky below and massive at depth. Drainage on both sites was free. A representative particle size analysis of the Ap horizon of soil from the experimental sites was: > 212/tm, 19.7%; 212-63/tm, 44.6%; 6 3 - 2 0 / t m , 14.3%; 20-2/~m, 9.7%, < 2 pm, 11.7%. The cultivation treatments in the first experiment (1975-1977) were mouldboard ploughing, shallow tine cultivation and direct drilling with the triple-disc coulter. In the second experiment (1978-1980), on a different site, the same treatments were applied, but two more direct-drilling treatments were added, the single dished disc and the disc plus tine coulters. These were chosen to produce different degrees of soil disturbance as the cereal seed was drilled. In 1980, the treatment drilled with the single dished coulter was replaced with a simulated 'tine-drill' which produced a degree of soil disturbance intermediate between that of the disc plus tine and shallow tine cultivation. Superimposed on these cultivation treatments were five rates of application of nitrogenous fertilizer. In the first experiment, an overall uniform rate of c o m p o u n d fertilizer (22% N : 11% P205: 11% K 2 0 ) was applied in the first year at 177 kg h a - ~, but in the second and third years the N rates were 35, 55, 75, 95 and 115 kg h a - ~. A basal dressing of 300 kg h a - ~ of a 0: 20% P205 : 20% K 2 0 fertilizer was broadcast before drilling. The N was applied as Nitrochalk (25% N) being combine drilled with the seed. In the second experiment, the N rates were 30, 60, 90, 120 and 150 kg ha-~, but the fertilizer was broadcast after drilling with a pneumatic distributor (Nodet Gougis DP 12). The basal dressing of phosphate and potash was combine drilled with the seed. The experimental design of both experiments was strip plots in randomised blocks with cultivation treatments in main plots and N treatments in subplots. Treatments were replicated six times in the first experiment and four times in the second. Main plot areas were 414 and 641 m E, and subplot areas 71 and 128 m 2 in the first and second experiments, respectively.
Management of the experiments Previous cropping on the first site was potatoes and on the second site winter wheat. Plots were ploughed with a three-furrow general purpose plough in December or January to a depth of 22-24 cm. Shallow tine cultivation was
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M.A. BRAIMET AL.
TABLE 1 Accumulated potential soil moisture deficits ( r a i n f a l l - p o t e n t i a l transpiration), April-August 19751980 ( m m ) Month
1975
1976
1977
1978
1979
1980
April May June July August
0 47 140 157 233
43 0 94 169 253
19 57 58 130 160
17 58 69 93 108
23 3 72 152 143
63 151 121 204 179
by a rigid-tined cultivator with a tine spacing of 30 cm. Two passes of the implement at right angles to each other and 10-12.5 cm deep were carried out in late autumn. To prepare the seed bed in the spring, the former treatment was harrowed twice and the latter once using a duck-foot harrow or springtined cultivator. The direct-drilled treatments were sprayed in early March with paraquat ( 1,1 '-dimethyl-4,4'-bipyridinium ion) to control volunteer cereals and other weeds. A Fernhurst triple-disc combine drill (coulter spacing 15.2 cm) was used to sow the barley seed in the first experiment and in the second a Bettinson direct drill (coulter spacing 17.5 cm). The three different types of coulter for this drill were interchangeable. The ploughed and tine-cultivated plots were also sown with these drills using the triple disc in the first experiment and the single dished disc in the second. After drilling, the whole site was normally lightly harrowed and rolled. Barley was sown at a rate to give a density of 300 seeds m -2. The variety was Sultan in 1975, Maris Mink in 1976 and 1977, and Athos from 1978 to 1980. Broad-leaved weeds (mainly Polygonum aviculare and Tripleurospermum inodorum) were controlled with post-emergence sprays and the main fungal disease, Erysiphe graminis, by ethirimol seed dressing and a fungicide spray when appropriate. After cutting the crop with a combine harvester, the straw was burnt in situ in Experiment 1, but in Experiment 2 the straw was removed and the stubble was not burnt. A spray of paraquat was usually applied in September or October to control volunteer barley and, in the autumn of 1979 only, glyphosate was used to control Agropyron repens. The dates of sowing from 1975 to 1980 were 12 April, 22 March, 5 April, 5 April, 19 April and 5 April, and the dates of harvesting were 20 August, 5 August, 7 September, 25 August, 26 August and 27 August. The accumulated potential soil moisture deficits are given in Table 1.
Records Plants were counted as they emerged on ten random samples of row each 2 m long so that the final number could be ascertained. During the growth of
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SIMPLIFIED CULTIVATION AND SPRING BARLEY. 1. SHOOTS
the crop, shoot dry mass was measured on random samples cut from 1 square metre, usually at Zadok's growth stage (GS) 31 and always at GS 65. Only the lowest, highest and intermediate N rates of each main plot were sampled. The N content of the dry matter was determined by the Kjeldahl method, modified to include the nitrate fraction (Clark, 1979). Grain yield was estimated from measured lengths of cut by a 2.6-m Claas Mercury combine harvester. After weighing, the fresh grain samples were taken for dry matter determination and the yields of grain corrected to 15% moisture content. Thousand-grain weights were determined from the sample and also corrected to 15% moisture content. Stem counts on ten random 1-m lengths of the cut stubble gave an estimate of the number of ears; the number of grains per ear was obtained from random samples of ~ 100 ears taken before harvest. Details of soil and root sampling are given in the second paper (Braim et al., 1991 ). RESULTS
In this paper, the results relating to shoot growth and yield are given with special reference to the uptake of N by the crop and the response of grain yield to nitrogenous fertilizer. The numbers of emerged plants are given in Table 2 as a mean of N rates. In the first experiment, the method of cultivation had no effect on the number of plants established in 1975 and 1977. In 1976, numbers were significantly greater after direct drilling than the other two tillage treatments; the poorer emergence on the latter was attributed to the loose 'puffy' nature of the seed TABLE 2 Effect o f m e t h o d o f cultivation ( m e a n s o f nitrogen rates ) on the n u m b e r o f e m e r g e d plants ( m - 2 ) Year
Cultivation Plough
SED Shallow tine
Direct-drill 3D
DT
1975 1976 1977
185 157 199
181 151 209
183 207 215
-
1978 1979 1980
221 246 195
214 243 196
194 244 74
198 242 104
SD -
5.7 11.5 7.4
187 216 (127)*
6.9 9.3 15.2
3 D = t r i p l e - d i s c coulter; D T = d i s c plus tine coulter; S D = d i s h e d - d i s c coulter; ( ) * = s i m u l a t e d fine drill; SED = s t a n d a r d error o f t h e difference.
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M.A. BRAIMETAL.
bed which led to seed being drilled too deep. The soil was also drier on the tilled plots than on those direct drilled and this too may have adversely affected establishment. In the second experiment, in 1978, plant numbers were slightly higher on the tilled than the direct-drilled plots, while the single dished disc gave significantly poorer establishment than the tilled treatments. This also occurred in 1979. In 1980, all the direct-drilled treatments gave significantly lower n u m b e r of plants than ploughing or shallow cultivation, the lowest numbers being after the triple disc. Seedling loss due to slugs was clearly evident on the direct-drilled plots. The yields of shoot dry matter at Zadok's GS 65 are given in Table 3 for each cultivation treatment at low and high rates of application of nitrogenous fertilizer. Responses to N were large and significant on all cultivation treatments, and although the interaction between cultivation treatment and N was significant in 1979 only, the mean response to N was largest after direct drilling and least after ploughing. This meant that at low levels of applied N, direct drilling gave a shoot yield 38% below that after ploughing, but at high levels of N the difference was only 13%. The corresponding figures for shallow cultivation compared with ploughing were 15 and 5%. Differences in shoot dry matter yield between the methods of direct drilling were in general non-significant at the higher levels of N application, but at the lower levels, in 1978 and 1979, barley drilled with the disc plus tine coulters yielded more than that drilled with the other two types. The uptake of N by the crops at the same stage of growth is given in Table TABLE 3 Effect of cultivation on the yield of shoot dry matter (Zadok's GS 65 ) at low and high levels of nitrogen application (g m - 2 ) , 1976-1980 Year
Cultivation
SED
Plough L
H
Shallow tine
Direct-drill
L
H
L
H
a
b
1976 1977
696 514
822 703
624 522
864 713
624 420
782 619
41.1 36.5
41.8 39.2
1978 1979 1980
617 732 645
735 1108 798
483 420 570
711 936 750
298 286 362
586 978 665
43.7 72.4 63.2
55.4 73.8 62.7
Mean
641
833
544
795
398
726
L = low nitrogen ( 30-35 kg N h a - J ); H = high nitrogen ( 115-150 kg N h a - t ); SED = standard error of the difference, (a) for L vs. H within cultivations, (b) for comparing cultivations within L or H; direct-drill = triple disc.
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SIMPLIFIEDCULTIVATIONAND SPRING BARLEY. I. SHOOTS
4. Regression lines were fitted to the N uptake of the shoots and the quantity of applied N. The N content of the shoots in the absence of fertilizer was then calculated from the regression equation. In addition, the apparent recovery of the applied N was given by the regression coefficient. The values indicate clearly that as the depth of soil loosening increased, the quantity of N in the shoots increased substantially, and these differences were not entirely eliminated by the application of N. Differences in the recovery of N between cultivation treatments were not consistent from year to year, but with the exception of 1979 tended to be least after direct drilling. Grain yields at low and high levels of N for 1976-1980 are given in Table 5. In 1975, when only a low rate of N was applied, the yield after ploughing was 6.81 t h a - i, direct drilling reducing yield by 16% and shallow cultivation by only 4%. In 1976, June and July were very dry (Table 1 ), the crops matured early and the differences present in the shoot yields at anthesis were not reflected in the grain yields. (There were no significant differences between cultivation treatments or N levels. ) In the other years, these main effects were highly significant and the interaction was significant in 1978 and 1979. Compared with the 5-year mean yields after ploughing of 5.07 and 6.14 t h a - 1 at low and high N levels, respectively, direct drilling reduced grain yield by 23% at low and by only 12% at high levels of N. Comparable figures for shallow tine cultivation were 11 and 3%. From the fitted quadratic curves in Fig. 1, it appears that by applying higher levels of N differences in grain yield between shallow tine cultivation and ploughing can be eliminated, but the differences between direct drilling and ploughing persist. The causes of these yield differences were analysed further in relation to components of grain yield. In Experiment 1, in 1975, there was no significant TABLE 4 Effect of cultivation on the mean uptake of nitrogen (kg N h a - ' ) by the shoots of barley (Zadok's GS 65 ) and on the recovery of fertilizer N (%), 1976-1980 Cultivation Plough
Shallow tine
Direct-drill
Mean of 1976 and 1977 Nil fertilizer 115 kg N h a - ' Apparent recovery
80.9 163.2 72.0
75.6 155.0 69.0
63.9 123.0 51.0
Mean of 1978-1980 Nil fertilizer 150 kg N h a - ' Apparent recovery
63.0 133.6 47.0
46.3 115.0 46.0
28.9 111.7 55.0
Direct-drill=triple disc in 1976 and 1977; mean of three coulters from 1978 to 1980.
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M.A. BRAIM ET AL.
TABLE 5
Effect of cultivation on the grain yield of barley (t h a - t at 85% dry matter) at low and high levels of nitrogen, 1976-1980 Year
Cultivation
SED
Plough
Shallow tine
Direct-drill
L
H
L
H
L
H
a
b
1976 1977
5.20 5.18
5.08 6.74
5.10 4.64
5.17 6.48
5.28 4.21
5.56 5.76
0.217 0.189
0.296 0.224
1978 1979 1980
5.59 4.72 4.68
6.08 6.59 6.21
4.88 3.44 4.42
6.28 6.12 5.79
3.58 2.31 4.01
5.64 5.30 4.63
0.243 0.225 0.228
0.304 0.262 0.208
Mean
5.07
6.14
4.50
5.97
3.88
5.38
L = low nitrogen ( 30-35 kg N h a - ~); H = high nitrogen ( 1 i 5-150 kg N ha - ~); SED = standard error of the difference, (a) for L vs. H within cultivations, (b) for comparing cultivations within L or H; direct-drill = triple disc.
1977
p
,.S""
35
"D >,
55
75
95
115
1978-80
.5
6
~.~-~"5
...... ~ ........
2
f
o
¢
,
ao
60
9'o
1~o
tgo
nitrogen kg ha -I
Fig. 1. The response o f barley grain yield to rates o f nitrogen fertilizer for three cultivation systems, ploughing ( p ) , shallow cultivation ( s ) and direct drilling ( d ) ; third year o f Experiment 1 ( 1 9 7 7 ) and the mean o f 3 years for Experiment 2 ( 1 9 7 8 - 1 9 8 0 ) . Quadratic regressions g a v e r 2 values > 0.96 for every response curve.
SIMPLIFIED CULTIVATION AND SPRING BARLEY. 1. SHOOTS
167
effect of method of cultivation on the numbers of ears, although the lowest yield was associated with the smallest number of ears. In 1976, tillage did not have a significant effect on number of ears, number of grains per ear or thousand-grain weight. Nitrogen increased the number of ears only, but this was not reflected in significantly higher grain yields. In 1977, the effects of tillage and N on the number of ears were similar to those in 1976, but direct drilling reduced the number of grains per ear from 21.9 after ploughing and from 21.4 after shallow cultivation to 20.5 ( P < 0.01 ). Shallow cultivation and direct drilling also reduced the thousand-grain weights from a mean value of 37.4 g after ploughing to 35.1 and 34.7 g, respectively ( P < 0.001 ). Shallow cultivation, therefore, limited the capacity of the crop to fill the grains, whereas direct drilling affected the crop before anthesis by reducing the number of spikelets and by restricting grain size after anthesis. In Experiment 2, from 1978 to 1980, the main component affecting grain yields was the number of ears. Both factors, tillage and N, had highly significant effects on this component, direct drilling giving mean numbers of 552, 442 and 558 per m E in 1978, 1979 and 1980, respectively, compared with 624, 580 and 652 per m 2 after ploughing. Shallow cultivation gave numbers which were intermediate. In contrast to Experiment l, the numbers of grains per ear were consistently increased by adding N to each tillage treatment, while thousand-grain weights decreased significantly except in 1980. The effects of tillage on the latter component were non-significant in 1978, but in 1979 the triple-disc treatment gave a value of 43.1 g compared with a mean of 41.7 g for the other four treatments ( P < 0 . 0 0 1 ) , and in 1980 ploughing gave the smallest weight (36.9 g) and direct drilling the largest (38.2 g), with shallow cultivation at 37.4 g (differences significant at P < 0.01 ). DISCUSSION
These experiments have shown conclusively that direct drilling of spring cereals on sandy soils with a high content of fine sand and coarse silt, and low clay content, is likely to incur a yield penalty compared with conventional tillage. This confirms the results obtained on a sandy soil of the Newport series where ploughing always produced greater grain yields of spring barley than direct drilling (Anon., 1977 ). In contrast, Elliott et al. ( 1977 ), working on a sandy loam with a higher coarse sand fraction and lower fine sand and silt fraction than the Wighill series, found that 4-year mean yields after direct drilling and ploughing were not significantly different, although in the first year direct-drilled barley yielded less than the other cultivation systems. In that year, however, less N was applied than in subsequent years and this suggested that differences between cultivation systems may be eliminated when large dressings of N are given and that the optimum levels of N fertilizer might differ between systems.
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M.A. B R A I M ET AL.
Hodgson et al. ( 1977 ) deduced from N uptake at anthesis that direct-drilled barley required 40 kg ha-1 more N than barley after ploughing to equalise uptakes at this stage of growth. Differences in N uptake, however, may not result in differences in grain yield. It has also been concluded from the results of a long-term experiment ( 1968-1978 ) on two soil types (a sandy loam over sandy clay and a sandy loam over clay) that direct-drilled barley required higher rates of N than barley after ploughing, but that differences in yield were largely eliminated at the highest application rate ( 150/180 kg N h a - 1) (R.W. Lang and J.C. Holmes, unpublished paper, East of Scotland College of Agriculture, 1979 ). The results from Askham Bryan in relation to N requirements are, therefore, of interest. Large applications of N reduced differences in shoot biomass between cultivation systems (Table 3), but did not eliminate them. Differences in N uptake at anthesis also persisted with increases in N fertilizer application (Table 4 ). These differences were reflected in grain yields, except that the yield after shallow cultivation was only slightly below that after ploughing with the highest rate of N applied, but after direct drilling the yield was substantially lower (Table 5 ). The quadratic regressions fitted to the N response data (Fig. 1 ) suggest that the yield of direct-drilled barley could not be raised to the yield after ploughing or shallow cultivation by applying larger quantities of N, and that factors other than inadequate N were limiting yield. These will be discussed more fully in the second paper (Braim et al., 1991 ). The reduction in yield of grain was usually associated with fewer ears. In 1975 and 1979, approximately equal numbers of plants established on the tillage treatments, but fewer tillers per plant were produced after direct drilling. In 1976, plant numbers were lower after ploughing and shallow cultivation than direct drilling, but the plants tillered more thus equalising numbers of ears per unit area. In 1978, the plants tillered equally well on all cultivation treatments, the differences in final ear numbers being related to plant numbers at establishment. Plant numbers after direct drilling were very low in 1980, but these plants had a high tillering capacity (up to 7.5 ears per plant) which compensated for the lower numbers. However, compensation was not sufficient to raise ear numbers to the numbers obtained on the ploughed plots. In 1977, plants on all tillage treatments tillered equally well (a mean of 4 ears per plant) and, as the numbers of plants were almost the same, there were no significant differences in the final ear number per unit area, yet grain yields differed significantly. Barley ears, after both ploughing and shallow tine cultivation, had the same number of grains, but in the latter grain weight was reduced. Direct-drilled barley not only had the smallest grain weight, but also a significantly lower number of grains per ear. It is clear, therefore, that direct-driUed barley was under stress during the period of ear development and suffered a higher degree of spikelet abortion than the other two treatments. This stress extended to the grain-filling period when barley after shallow tine
SIMPLIFIEDCULTIVATIONAND SPRING BARLEY.1. SHOOTS
169
cultivation was also affected. It is the duration of grain filling rather than the rate of grain filling which would have brought about the differences in grain size; these crops matured slightly earlier. It is probable, therefore, that the factor which limited growth came into operation at successively earlier stages with less and less soil disturbance. The grain yield vs. N response curves enable an economic analysis of fertilizer N requirements. It is important to determine whether there are differences in the optimum requirements between the three systems. The most profitable rates of N application were calculated using the formula Nopt = ( b - ( q / p ) ) / 2 c where q and p are the price of the product and the price of N per kg, respectively, and b and c are the coefficients of N and N z, respectively, in the quadratic equations. From Table 6, it is clear that apart from shallow tine cultivation ( 19781980), the N requirements for the three systems are very similar. However, the yield level is much lower for direct drilling than ploughing or shallow tine cultivation. Consequently, there is a substantial reduction in the margin between gross returns and fertilizer cost of £73 to £87 h a - 1. Unless direct drilling can effect economies of at least this amount in terms of reduced machinery and fuel costs, then for this soil type, unlike the heavier soils, the system is uneconomic for spring barley production. Finally, there is little difference between the types of coulter used for direct drilling. Apart from 1980, the triple disc has given good plant establishment, as also has the disc plus tine. In contrast, the dished-disc coulter gave the poorest establishment in the 2 years it was tested. This appeared to be due to TABLE6 Effect of cultivation system on the optimum rate of nitrogen for spring barley and net margins (gross financial returns-cost of N fertilizer) Cultivation
Experiment 1 1977 Plough Shallow tine Direct-drill
Nopt (kgha - I )
Cost of N (£ha -j)
Yield (tha -j)
Gross output (£ha - t )
Margin (£ha - l )
120 120 127
48 48 50.8
6.64 6.50 5.80
664 650 580
616 602 529
52 74 52
6.19 6.30 5.35
619 630 535
567 556 483
Experiment 2 (Mean 1978-1980 ) Plough 130 Shallow tine 185 Direct-drill 130
Grain valued at £ 100 t - t; cost of nitrogen 40 p kg- t.
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M.A.BRAIMET AL.
the concave surface of the disc causing the seed to be deposited beneath the slabs of soil which were formed as the coulters cut into the soil. The simulated 'tine-drill' treatment tested in 1980 gave much better plant establishment than the triple disc or disc plus tine, but the extra soil disturbance did not significantly enhance either N uptake or grain yield. Cultivating the soil to a depth of 10 cm appears to be necessary to achieve a yield equal to ploughing at 22-24 cm, but an additional 55 kg N h a - l above the optimum rate for ploughing may be required. CONCLUSIONS
( 1 ) Direct-drilled spring barley yields significantly less grain than barley after ploughing at all rates of N application. (2) Shallow tine cultivation ( 10-12.5 cm) produces grain yields equal to ploughing at higher rates of N application ( 115-150 kg h a - 1), but not at lower rates. ( 3 ) The different degrees of soil disturbance caused by different designs of drill coulter did not have a significant effect on the yield of direct-drilled barley. (4) Less N is taken up by the shoots of direct-drilled barley than of barley after ploughing, but in terms of grain production this does not result in a difference between the optimum (most profitable) quantities of N for the two systems. ( 5 ) At optimum rates of N, barley after ploughing or shallow tine cultivation produces a greater net margin than direct-drilled barley on this sandy loam soil. ACKNOWLEDGEMENTS
The authors thank the Agricultural and Food Research Council for financial support. Thanks are also due to Mr. L. Gilling, Principal of Askham Bryan College of Agriculture and Horticulture, when these experiments were carried out, for providing the sites and to Mr. P.C. Manning, Farm Manager, for much practical help. We are grateful for the assistance of the staff of the Agronomy Unit at the University of Leeds Field Station, and for the supervision of Experiment 1 by Dr. B.J. Clutterbuck.
REFERENCES Anonymous, 1977. Sandland barley booklet. Gleadthorpe Experimental Husbandry Farm. Agricultural Development and Advisory Service, Ministry of Agriculture, Fisheries and Food, England and Wales, 60 pp. Bakermans, W.A.P. and de Wit, C.T., 1970. Crop husbandry on naturally compacted soils. Neth. J. Agric. Sci., 18: 225-246.
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Braim, M.A., Chaney, K. and Hodgson, D.R., 1984. Preliminary investigation on the response of spring barley (Hordeumsativum) to soil cultivation with the 'Paraplow'. Soil Tillage Res., 4: 277-293. Braim, M.A., Chaney, K. and Hodgson, D.R., 1992. Effects of simplified cultivation on the growth and yield of spring barley on a sandy loam soil. 2. Soil physical properties and root growth; root: shoot relationships; inflow rates of nitrogen; water use. Soil Tillage Res., 22: 173-187. Cannell, R.Q., 1985. Reduced tillage in North West Europe - a review. Soil Tillage Res., 5: i 29177. Chaney, K., Hodgson, D.R. and Braim, M.A., 1985. Effects of direct drilling, shallow cultivation and ploughing on some soil physical properties in a long-term experiment on spring barley. J. Agric. Sci., 104: 125-133. Clark, A.J., 1979. Total nitrogen estimation in herbage and soils using the gas-sensing electrode. Lab. Pract., 28: 1076-1078. Clutterbuck, B.J. and Hodgson, D.R., 1984. Direct drilling and shallow cultivation compared with ploughing for spring barley in northern England. J. Agric. Sci., 102:127-134. Crompton, A. and Matthews, B., 1970. Soils of the Leeds district. Agricultural Research Council, Memoirs of the Soil Survey of Great Britain, Harpenden, 221 pp. Elliott, J.G., Ellis, F.B. and Pollard, F., 1977. Comparison of direct drilling, reduced cultivation and ploughing on the growth of cereals. I. Spring barley on a sandy loam s,gil: introduction, aerial growth and agronomic aspects. J. Agric. Sci., 89: 621-629. Ellis, F.B., Elliott, J.G., Barnes, B.T. and House, F.R., 1977. Comparison of direct drilling, reduced cultivation and ploughing on the growth of cereals. 2. Spring barley on a sandy loam soil: soil physical conditions and root growth. J. Agric. Sci., 89:631-642. Frankinet, M., Rixhon, L., Crohain, A. and Grevey, L., 1979. Labour, demi-labour on semis direct en continu consequences phytotechniques. Bull. Rech. Agron. Gernbloux, 14: 35-96. Hodgson, D.R., Proud, J.R. and Browne, S., 1977. Cultivation systems for spring barley with special reference to direct drilling ( 1971-1974). J. Agric. Sci., 88:631-644. Holmes, J.C., 1977. Effects of tillage, direct drilling and nitrogen in a long term monoculture system. Edinburgh School of Agriculture, Annual Report, 1976, pp. 104-I 12. O'Sullivan, M.F. and Ball, B.C., 1982. Spring barley growth, grain quality and soil physical conditions in a cultivation experiment on a sandy loam in Scotland. Soil Tillage Res., 2: 359378. Patterson, D.E., Chamen, W.C.T. and Richardson, C.D., 1980. Long term experiment with tillage systems to improve the economy of cultivations for cereals. J. Agric. Eng. Res., 25: 135.
Pidgeon, J.D., 1981. A preliminary study of minimum tillage systems (including broadcasting) for spring barley in Scotland. Soil Tillage Res., 1: 139-151. Pidgeon, J.D. and Soane, B.D., 1977. Effects of tillage and direct drilling on soil properties during the growing season of a long-term barley monoculture system. J. Agric. Sci., 83:431442. Pollard, F., Elliott, J.G., Ellis, F.B. and Barnes, B.T., 1981. Comparison of direct drilling, reduced cultivation and ploughing on the growth of cereals. 4. Spring barley and winter wheat on silt loam soils over chalk. J. Agric. Sci., 97: 677-684. Sharma, R.B., 1985. Plant-water relations, crop growth and grain yield of spring barley in relation to tillage methods. Soil Tillage Res., 6:111-121. Ten Holte, L., 1982. Effect of zero tillage on soil characteristics and crop yields. Proceedings of the 9th Conference of the International Soil Tillage Research Organization, ISTRO, Osijek, Yugoslavia, pp. 118-124.
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Effects of simplified cultivation on the growth and yield of spring barley on a sandy loam soil. 1. Shoot growth and grain yield; response to nitrogen M.A. Braim ~, K. Chaney 2 and D.R. Hodgson Department of Pure and Applied Biology, University of Leeds, Leeds LS2 9JT, UK (Accepted 20 November 1990)
ABSTRACT Braim, M.A., Chaney, K. and Hodgson, D.R., 1992. Effects of simplified cultivation on the growth and yield of spring barley on a sandy loam soil. I. Shoot growth and grain yield; response to nitrogen. Soil Tillage Res., 22:159-17 I. Two experiments, each of three years duration ( 1975-1977 and 1978-1980), were carried out on a sandy loam soil to investigate the effects of mouldboard ploughing, shallow tine cultivation and direct drilling on the growth and yield of spring barley receiving different rates of application of nitrogenous fertilizer. Grain yields of the ploughed and shallow-cultivated treatments were similar ( ~ 6 t ha- ~) provided optimum amounts of nitrogenous fertilizer were applied, but direct drilling reduced yield, on average by 23% at 30-35 kg nitrogen (N) ha -~ and by 12% at 115-150 kg N ha -~. The direct cause of the reduction in grain yield after direct drilling compared with ploughing was a lower number of ears, except in 1977 when the difference was due to a smaller number of grains per ear and a lower thousand-grain weight. In the absence of nitrogenous fertilizer, less N was taken up by direct-driUed barley during its growth than by barley grown after ploughing or shallow tine cultivation, and there was still a difference at the highest level of fertilizer applied. The most profitable rates of N application were calculated for each cultivation system from fitted quadratic equations. These optimum rates were similar for all cultivation treatments in the final year of the first experiment ( ~ 120 kg N h a - l ), and were similar for direct drilling and ploughing in the second experiment ( ~ 130 kg N ha- ~), whereas the optimum for shallow cultivation was 185 kg N ha- i. At prevailing grain and fertilizer prices, the margin over fertilizer costs was between £73 and £87 ha- ~less from direct drilling than from ploughing or shallow tine cultivation.
INTRODUCTION In a comprehensive review, Cannell ( 1985 ) presented the results of many tillage experiments carried out in northwest Europe during the 1960s and Present addresses: ~Corpslanding, Hutton Cranswick, Driffield, N. Humberside, YO25 9QF, UK; 2Levington Agriculture Ltd., Ipswich, Suffolk, IP 10 0LU, UK.
© 1992 Elsevier Science Publishers B.V. All fights reserved 0167-1987/92/$05.00
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1970s to compare direct drilling and other simplified cultivation systems with conventional mouldboard ploughing. On a wide variety of soil types, crops of direct-drilled winter wheat have given yields very similar to crops grown using conventional tillage. Spring barley, however, has given more variable results following direct drilling. In the UK, similar yields have been reported after direct drilling, shallow tillage and ploughing on clay loams (Ellis et al., 1977; Patterson et al., 1980; Clutterbuck and Hodgson, 1984), on a welldrained sandy loam (Elliott et al., 1977) and on a rendzina (Pollard et al., 1981 ). On a sandy clay loam, Chaney et al. (1985 ) reported that over a 10year period of continuous cropping with spring barley, mean grain yields were marginally lower after direct drilling than after shallow cultivation or ploughing. In Scotland, Holmes ( 1977 ), Pidgeon and Soane ( 1977 ), Pidgeon ( 1981 ) and O'Sullivan and Ball (1982), working on soils with impeded drainage, found that direct-drilled crops were lower yielding than those following ploughing. In The Netherlands, on a sandy soil, direct drilling and ploughing produced similar yields of spring barley (Bakermans and de Wit, 1970; Ten Holte, 1982), but in Belgium on a loess, Frankinet et al. (1979) reported a 15% reduction in yield after direct drilling. That yields of spring barley can be significantly greater after direct drilling than after ploughing was shown by Braim et al. (1984). This was due to a plough pan in the latter treatment causing transient waterlogging during an unusually wet spring. Mineral soils with a high proportion of coarse and fine sand are unstable structurally, easily become compacted and, because of the low content of colloidal material, natural fissures for the penetration of roots are few. These soils may not, therefore, be suitable for direct drilling of cereals, some soil disturbance being necessary for achieving satisfactory yields, particularly of spring-sown cereals. Two experiments, each of 3 years duration, were started on a sandy soil in Northern England, one in 1975 and the other in 1978, to compare direct drilling and shallow tine cultivation with mouldboard ploughing. The absence of cultivation reduces the uptake of nitrogen (N) by the crop (Hodgson et al., 1977; Clutterbuck and Hodgson, 1984), therefore each cultivation treatment received increasing rates of application of nitrogenous fertilizer so that the N factor might be eliminated from comparisons between tillage treatments. In this paper, results relating to yields, responses to N and N uptake by shoots of spring barley are presented. The effects of treatments on soil properties and root growth, with special reference to the efficiency of the root system and water use by the crop, are described in a second paper (Braim et al., 1991 ). Sharma ( 1985 ) reported results relating to 1976 only.
SIMPLIFIED CULTIVATION AND SPRING BARLEY. 1. SHOOTS
161
MATERIALSAND METHODS The experiments were conducted on two field sites at Askham Bryan College of Agriculture and Horticulture, near York, North Yorkshire. The soil of both sites is a stagnogleyic argillic brown earth classified by the Soil Survey of England and Wales as the Wighill series ( C r o m p t o n and Matthews, 1970 ). A sandy loam with sandstone cobbles and pebbles merges into a sandy clay loam at ~ 45 cm; structure at the surface is weak, becoming coarse subangular blocky below and massive at depth. Drainage on both sites was free. A representative particle size analysis of the Ap horizon of soil from the experimental sites was: > 212/tm, 19.7%; 212-63/tm, 44.6%; 6 3 - 2 0 / t m , 14.3%; 20-2/~m, 9.7%, < 2 pm, 11.7%. The cultivation treatments in the first experiment (1975-1977) were mouldboard ploughing, shallow tine cultivation and direct drilling with the triple-disc coulter. In the second experiment (1978-1980), on a different site, the same treatments were applied, but two more direct-drilling treatments were added, the single dished disc and the disc plus tine coulters. These were chosen to produce different degrees of soil disturbance as the cereal seed was drilled. In 1980, the treatment drilled with the single dished coulter was replaced with a simulated 'tine-drill' which produced a degree of soil disturbance intermediate between that of the disc plus tine and shallow tine cultivation. Superimposed on these cultivation treatments were five rates of application of nitrogenous fertilizer. In the first experiment, an overall uniform rate of c o m p o u n d fertilizer (22% N : 11% P205: 11% K 2 0 ) was applied in the first year at 177 kg h a - ~, but in the second and third years the N rates were 35, 55, 75, 95 and 115 kg h a - ~. A basal dressing of 300 kg h a - ~ of a 0: 20% P205 : 20% K 2 0 fertilizer was broadcast before drilling. The N was applied as Nitrochalk (25% N) being combine drilled with the seed. In the second experiment, the N rates were 30, 60, 90, 120 and 150 kg ha-~, but the fertilizer was broadcast after drilling with a pneumatic distributor (Nodet Gougis DP 12). The basal dressing of phosphate and potash was combine drilled with the seed. The experimental design of both experiments was strip plots in randomised blocks with cultivation treatments in main plots and N treatments in subplots. Treatments were replicated six times in the first experiment and four times in the second. Main plot areas were 414 and 641 m E, and subplot areas 71 and 128 m 2 in the first and second experiments, respectively.
Management of the experiments Previous cropping on the first site was potatoes and on the second site winter wheat. Plots were ploughed with a three-furrow general purpose plough in December or January to a depth of 22-24 cm. Shallow tine cultivation was
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M.A. BRAIMET AL.
TABLE 1 Accumulated potential soil moisture deficits ( r a i n f a l l - p o t e n t i a l transpiration), April-August 19751980 ( m m ) Month
1975
1976
1977
1978
1979
1980
April May June July August
0 47 140 157 233
43 0 94 169 253
19 57 58 130 160
17 58 69 93 108
23 3 72 152 143
63 151 121 204 179
by a rigid-tined cultivator with a tine spacing of 30 cm. Two passes of the implement at right angles to each other and 10-12.5 cm deep were carried out in late autumn. To prepare the seed bed in the spring, the former treatment was harrowed twice and the latter once using a duck-foot harrow or springtined cultivator. The direct-drilled treatments were sprayed in early March with paraquat ( 1,1 '-dimethyl-4,4'-bipyridinium ion) to control volunteer cereals and other weeds. A Fernhurst triple-disc combine drill (coulter spacing 15.2 cm) was used to sow the barley seed in the first experiment and in the second a Bettinson direct drill (coulter spacing 17.5 cm). The three different types of coulter for this drill were interchangeable. The ploughed and tine-cultivated plots were also sown with these drills using the triple disc in the first experiment and the single dished disc in the second. After drilling, the whole site was normally lightly harrowed and rolled. Barley was sown at a rate to give a density of 300 seeds m -2. The variety was Sultan in 1975, Maris Mink in 1976 and 1977, and Athos from 1978 to 1980. Broad-leaved weeds (mainly Polygonum aviculare and Tripleurospermum inodorum) were controlled with post-emergence sprays and the main fungal disease, Erysiphe graminis, by ethirimol seed dressing and a fungicide spray when appropriate. After cutting the crop with a combine harvester, the straw was burnt in situ in Experiment 1, but in Experiment 2 the straw was removed and the stubble was not burnt. A spray of paraquat was usually applied in September or October to control volunteer barley and, in the autumn of 1979 only, glyphosate was used to control Agropyron repens. The dates of sowing from 1975 to 1980 were 12 April, 22 March, 5 April, 5 April, 19 April and 5 April, and the dates of harvesting were 20 August, 5 August, 7 September, 25 August, 26 August and 27 August. The accumulated potential soil moisture deficits are given in Table 1.
Records Plants were counted as they emerged on ten random samples of row each 2 m long so that the final number could be ascertained. During the growth of
163
SIMPLIFIED CULTIVATION AND SPRING BARLEY. 1. SHOOTS
the crop, shoot dry mass was measured on random samples cut from 1 square metre, usually at Zadok's growth stage (GS) 31 and always at GS 65. Only the lowest, highest and intermediate N rates of each main plot were sampled. The N content of the dry matter was determined by the Kjeldahl method, modified to include the nitrate fraction (Clark, 1979). Grain yield was estimated from measured lengths of cut by a 2.6-m Claas Mercury combine harvester. After weighing, the fresh grain samples were taken for dry matter determination and the yields of grain corrected to 15% moisture content. Thousand-grain weights were determined from the sample and also corrected to 15% moisture content. Stem counts on ten random 1-m lengths of the cut stubble gave an estimate of the number of ears; the number of grains per ear was obtained from random samples of ~ 100 ears taken before harvest. Details of soil and root sampling are given in the second paper (Braim et al., 1991 ). RESULTS
In this paper, the results relating to shoot growth and yield are given with special reference to the uptake of N by the crop and the response of grain yield to nitrogenous fertilizer. The numbers of emerged plants are given in Table 2 as a mean of N rates. In the first experiment, the method of cultivation had no effect on the number of plants established in 1975 and 1977. In 1976, numbers were significantly greater after direct drilling than the other two tillage treatments; the poorer emergence on the latter was attributed to the loose 'puffy' nature of the seed TABLE 2 Effect o f m e t h o d o f cultivation ( m e a n s o f nitrogen rates ) on the n u m b e r o f e m e r g e d plants ( m - 2 ) Year
Cultivation Plough
SED Shallow tine
Direct-drill 3D
DT
1975 1976 1977
185 157 199
181 151 209
183 207 215
-
1978 1979 1980
221 246 195
214 243 196
194 244 74
198 242 104
SD -
5.7 11.5 7.4
187 216 (127)*
6.9 9.3 15.2
3 D = t r i p l e - d i s c coulter; D T = d i s c plus tine coulter; S D = d i s h e d - d i s c coulter; ( ) * = s i m u l a t e d fine drill; SED = s t a n d a r d error o f t h e difference.
164
M.A. BRAIMETAL.
bed which led to seed being drilled too deep. The soil was also drier on the tilled plots than on those direct drilled and this too may have adversely affected establishment. In the second experiment, in 1978, plant numbers were slightly higher on the tilled than the direct-drilled plots, while the single dished disc gave significantly poorer establishment than the tilled treatments. This also occurred in 1979. In 1980, all the direct-drilled treatments gave significantly lower n u m b e r of plants than ploughing or shallow cultivation, the lowest numbers being after the triple disc. Seedling loss due to slugs was clearly evident on the direct-drilled plots. The yields of shoot dry matter at Zadok's GS 65 are given in Table 3 for each cultivation treatment at low and high rates of application of nitrogenous fertilizer. Responses to N were large and significant on all cultivation treatments, and although the interaction between cultivation treatment and N was significant in 1979 only, the mean response to N was largest after direct drilling and least after ploughing. This meant that at low levels of applied N, direct drilling gave a shoot yield 38% below that after ploughing, but at high levels of N the difference was only 13%. The corresponding figures for shallow cultivation compared with ploughing were 15 and 5%. Differences in shoot dry matter yield between the methods of direct drilling were in general non-significant at the higher levels of N application, but at the lower levels, in 1978 and 1979, barley drilled with the disc plus tine coulters yielded more than that drilled with the other two types. The uptake of N by the crops at the same stage of growth is given in Table TABLE 3 Effect of cultivation on the yield of shoot dry matter (Zadok's GS 65 ) at low and high levels of nitrogen application (g m - 2 ) , 1976-1980 Year
Cultivation
SED
Plough L
H
Shallow tine
Direct-drill
L
H
L
H
a
b
1976 1977
696 514
822 703
624 522
864 713
624 420
782 619
41.1 36.5
41.8 39.2
1978 1979 1980
617 732 645
735 1108 798
483 420 570
711 936 750
298 286 362
586 978 665
43.7 72.4 63.2
55.4 73.8 62.7
Mean
641
833
544
795
398
726
L = low nitrogen ( 30-35 kg N h a - J ); H = high nitrogen ( 115-150 kg N h a - t ); SED = standard error of the difference, (a) for L vs. H within cultivations, (b) for comparing cultivations within L or H; direct-drill = triple disc.
165
SIMPLIFIEDCULTIVATIONAND SPRING BARLEY. I. SHOOTS
4. Regression lines were fitted to the N uptake of the shoots and the quantity of applied N. The N content of the shoots in the absence of fertilizer was then calculated from the regression equation. In addition, the apparent recovery of the applied N was given by the regression coefficient. The values indicate clearly that as the depth of soil loosening increased, the quantity of N in the shoots increased substantially, and these differences were not entirely eliminated by the application of N. Differences in the recovery of N between cultivation treatments were not consistent from year to year, but with the exception of 1979 tended to be least after direct drilling. Grain yields at low and high levels of N for 1976-1980 are given in Table 5. In 1975, when only a low rate of N was applied, the yield after ploughing was 6.81 t h a - i, direct drilling reducing yield by 16% and shallow cultivation by only 4%. In 1976, June and July were very dry (Table 1 ), the crops matured early and the differences present in the shoot yields at anthesis were not reflected in the grain yields. (There were no significant differences between cultivation treatments or N levels. ) In the other years, these main effects were highly significant and the interaction was significant in 1978 and 1979. Compared with the 5-year mean yields after ploughing of 5.07 and 6.14 t h a - 1 at low and high N levels, respectively, direct drilling reduced grain yield by 23% at low and by only 12% at high levels of N. Comparable figures for shallow tine cultivation were 11 and 3%. From the fitted quadratic curves in Fig. 1, it appears that by applying higher levels of N differences in grain yield between shallow tine cultivation and ploughing can be eliminated, but the differences between direct drilling and ploughing persist. The causes of these yield differences were analysed further in relation to components of grain yield. In Experiment 1, in 1975, there was no significant TABLE 4 Effect of cultivation on the mean uptake of nitrogen (kg N h a - ' ) by the shoots of barley (Zadok's GS 65 ) and on the recovery of fertilizer N (%), 1976-1980 Cultivation Plough
Shallow tine
Direct-drill
Mean of 1976 and 1977 Nil fertilizer 115 kg N h a - ' Apparent recovery
80.9 163.2 72.0
75.6 155.0 69.0
63.9 123.0 51.0
Mean of 1978-1980 Nil fertilizer 150 kg N h a - ' Apparent recovery
63.0 133.6 47.0
46.3 115.0 46.0
28.9 111.7 55.0
Direct-drill=triple disc in 1976 and 1977; mean of three coulters from 1978 to 1980.
166
M.A. BRAIM ET AL.
TABLE 5
Effect of cultivation on the grain yield of barley (t h a - t at 85% dry matter) at low and high levels of nitrogen, 1976-1980 Year
Cultivation
SED
Plough
Shallow tine
Direct-drill
L
H
L
H
L
H
a
b
1976 1977
5.20 5.18
5.08 6.74
5.10 4.64
5.17 6.48
5.28 4.21
5.56 5.76
0.217 0.189
0.296 0.224
1978 1979 1980
5.59 4.72 4.68
6.08 6.59 6.21
4.88 3.44 4.42
6.28 6.12 5.79
3.58 2.31 4.01
5.64 5.30 4.63
0.243 0.225 0.228
0.304 0.262 0.208
Mean
5.07
6.14
4.50
5.97
3.88
5.38
L = low nitrogen ( 30-35 kg N h a - ~); H = high nitrogen ( 1 i 5-150 kg N ha - ~); SED = standard error of the difference, (a) for L vs. H within cultivations, (b) for comparing cultivations within L or H; direct-drill = triple disc.
1977
p
,.S""
35
"D >,
55
75
95
115
1978-80
.5
6
~.~-~"5
...... ~ ........
2
f
o
¢
,
ao
60
9'o
1~o
tgo
nitrogen kg ha -I
Fig. 1. The response o f barley grain yield to rates o f nitrogen fertilizer for three cultivation systems, ploughing ( p ) , shallow cultivation ( s ) and direct drilling ( d ) ; third year o f Experiment 1 ( 1 9 7 7 ) and the mean o f 3 years for Experiment 2 ( 1 9 7 8 - 1 9 8 0 ) . Quadratic regressions g a v e r 2 values > 0.96 for every response curve.
SIMPLIFIED CULTIVATION AND SPRING BARLEY. 1. SHOOTS
167
effect of method of cultivation on the numbers of ears, although the lowest yield was associated with the smallest number of ears. In 1976, tillage did not have a significant effect on number of ears, number of grains per ear or thousand-grain weight. Nitrogen increased the number of ears only, but this was not reflected in significantly higher grain yields. In 1977, the effects of tillage and N on the number of ears were similar to those in 1976, but direct drilling reduced the number of grains per ear from 21.9 after ploughing and from 21.4 after shallow cultivation to 20.5 ( P < 0.01 ). Shallow cultivation and direct drilling also reduced the thousand-grain weights from a mean value of 37.4 g after ploughing to 35.1 and 34.7 g, respectively ( P < 0.001 ). Shallow cultivation, therefore, limited the capacity of the crop to fill the grains, whereas direct drilling affected the crop before anthesis by reducing the number of spikelets and by restricting grain size after anthesis. In Experiment 2, from 1978 to 1980, the main component affecting grain yields was the number of ears. Both factors, tillage and N, had highly significant effects on this component, direct drilling giving mean numbers of 552, 442 and 558 per m E in 1978, 1979 and 1980, respectively, compared with 624, 580 and 652 per m 2 after ploughing. Shallow cultivation gave numbers which were intermediate. In contrast to Experiment l, the numbers of grains per ear were consistently increased by adding N to each tillage treatment, while thousand-grain weights decreased significantly except in 1980. The effects of tillage on the latter component were non-significant in 1978, but in 1979 the triple-disc treatment gave a value of 43.1 g compared with a mean of 41.7 g for the other four treatments ( P < 0 . 0 0 1 ) , and in 1980 ploughing gave the smallest weight (36.9 g) and direct drilling the largest (38.2 g), with shallow cultivation at 37.4 g (differences significant at P < 0.01 ). DISCUSSION
These experiments have shown conclusively that direct drilling of spring cereals on sandy soils with a high content of fine sand and coarse silt, and low clay content, is likely to incur a yield penalty compared with conventional tillage. This confirms the results obtained on a sandy soil of the Newport series where ploughing always produced greater grain yields of spring barley than direct drilling (Anon., 1977 ). In contrast, Elliott et al. ( 1977 ), working on a sandy loam with a higher coarse sand fraction and lower fine sand and silt fraction than the Wighill series, found that 4-year mean yields after direct drilling and ploughing were not significantly different, although in the first year direct-drilled barley yielded less than the other cultivation systems. In that year, however, less N was applied than in subsequent years and this suggested that differences between cultivation systems may be eliminated when large dressings of N are given and that the optimum levels of N fertilizer might differ between systems.
168
M.A. B R A I M ET AL.
Hodgson et al. ( 1977 ) deduced from N uptake at anthesis that direct-drilled barley required 40 kg ha-1 more N than barley after ploughing to equalise uptakes at this stage of growth. Differences in N uptake, however, may not result in differences in grain yield. It has also been concluded from the results of a long-term experiment ( 1968-1978 ) on two soil types (a sandy loam over sandy clay and a sandy loam over clay) that direct-drilled barley required higher rates of N than barley after ploughing, but that differences in yield were largely eliminated at the highest application rate ( 150/180 kg N h a - 1) (R.W. Lang and J.C. Holmes, unpublished paper, East of Scotland College of Agriculture, 1979 ). The results from Askham Bryan in relation to N requirements are, therefore, of interest. Large applications of N reduced differences in shoot biomass between cultivation systems (Table 3), but did not eliminate them. Differences in N uptake at anthesis also persisted with increases in N fertilizer application (Table 4 ). These differences were reflected in grain yields, except that the yield after shallow cultivation was only slightly below that after ploughing with the highest rate of N applied, but after direct drilling the yield was substantially lower (Table 5 ). The quadratic regressions fitted to the N response data (Fig. 1 ) suggest that the yield of direct-drilled barley could not be raised to the yield after ploughing or shallow cultivation by applying larger quantities of N, and that factors other than inadequate N were limiting yield. These will be discussed more fully in the second paper (Braim et al., 1991 ). The reduction in yield of grain was usually associated with fewer ears. In 1975 and 1979, approximately equal numbers of plants established on the tillage treatments, but fewer tillers per plant were produced after direct drilling. In 1976, plant numbers were lower after ploughing and shallow cultivation than direct drilling, but the plants tillered more thus equalising numbers of ears per unit area. In 1978, the plants tillered equally well on all cultivation treatments, the differences in final ear numbers being related to plant numbers at establishment. Plant numbers after direct drilling were very low in 1980, but these plants had a high tillering capacity (up to 7.5 ears per plant) which compensated for the lower numbers. However, compensation was not sufficient to raise ear numbers to the numbers obtained on the ploughed plots. In 1977, plants on all tillage treatments tillered equally well (a mean of 4 ears per plant) and, as the numbers of plants were almost the same, there were no significant differences in the final ear number per unit area, yet grain yields differed significantly. Barley ears, after both ploughing and shallow tine cultivation, had the same number of grains, but in the latter grain weight was reduced. Direct-drilled barley not only had the smallest grain weight, but also a significantly lower number of grains per ear. It is clear, therefore, that direct-driUed barley was under stress during the period of ear development and suffered a higher degree of spikelet abortion than the other two treatments. This stress extended to the grain-filling period when barley after shallow tine
SIMPLIFIEDCULTIVATIONAND SPRING BARLEY.1. SHOOTS
169
cultivation was also affected. It is the duration of grain filling rather than the rate of grain filling which would have brought about the differences in grain size; these crops matured slightly earlier. It is probable, therefore, that the factor which limited growth came into operation at successively earlier stages with less and less soil disturbance. The grain yield vs. N response curves enable an economic analysis of fertilizer N requirements. It is important to determine whether there are differences in the optimum requirements between the three systems. The most profitable rates of N application were calculated using the formula Nopt = ( b - ( q / p ) ) / 2 c where q and p are the price of the product and the price of N per kg, respectively, and b and c are the coefficients of N and N z, respectively, in the quadratic equations. From Table 6, it is clear that apart from shallow tine cultivation ( 19781980), the N requirements for the three systems are very similar. However, the yield level is much lower for direct drilling than ploughing or shallow tine cultivation. Consequently, there is a substantial reduction in the margin between gross returns and fertilizer cost of £73 to £87 h a - 1. Unless direct drilling can effect economies of at least this amount in terms of reduced machinery and fuel costs, then for this soil type, unlike the heavier soils, the system is uneconomic for spring barley production. Finally, there is little difference between the types of coulter used for direct drilling. Apart from 1980, the triple disc has given good plant establishment, as also has the disc plus tine. In contrast, the dished-disc coulter gave the poorest establishment in the 2 years it was tested. This appeared to be due to TABLE6 Effect of cultivation system on the optimum rate of nitrogen for spring barley and net margins (gross financial returns-cost of N fertilizer) Cultivation
Experiment 1 1977 Plough Shallow tine Direct-drill
Nopt (kgha - I )
Cost of N (£ha -j)
Yield (tha -j)
Gross output (£ha - t )
Margin (£ha - l )
120 120 127
48 48 50.8
6.64 6.50 5.80
664 650 580
616 602 529
52 74 52
6.19 6.30 5.35
619 630 535
567 556 483
Experiment 2 (Mean 1978-1980 ) Plough 130 Shallow tine 185 Direct-drill 130
Grain valued at £ 100 t - t; cost of nitrogen 40 p kg- t.
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the concave surface of the disc causing the seed to be deposited beneath the slabs of soil which were formed as the coulters cut into the soil. The simulated 'tine-drill' treatment tested in 1980 gave much better plant establishment than the triple disc or disc plus tine, but the extra soil disturbance did not significantly enhance either N uptake or grain yield. Cultivating the soil to a depth of 10 cm appears to be necessary to achieve a yield equal to ploughing at 22-24 cm, but an additional 55 kg N h a - l above the optimum rate for ploughing may be required. CONCLUSIONS
( 1 ) Direct-drilled spring barley yields significantly less grain than barley after ploughing at all rates of N application. (2) Shallow tine cultivation ( 10-12.5 cm) produces grain yields equal to ploughing at higher rates of N application ( 115-150 kg h a - 1), but not at lower rates. ( 3 ) The different degrees of soil disturbance caused by different designs of drill coulter did not have a significant effect on the yield of direct-drilled barley. (4) Less N is taken up by the shoots of direct-drilled barley than of barley after ploughing, but in terms of grain production this does not result in a difference between the optimum (most profitable) quantities of N for the two systems. ( 5 ) At optimum rates of N, barley after ploughing or shallow tine cultivation produces a greater net margin than direct-drilled barley on this sandy loam soil. ACKNOWLEDGEMENTS
The authors thank the Agricultural and Food Research Council for financial support. Thanks are also due to Mr. L. Gilling, Principal of Askham Bryan College of Agriculture and Horticulture, when these experiments were carried out, for providing the sites and to Mr. P.C. Manning, Farm Manager, for much practical help. We are grateful for the assistance of the staff of the Agronomy Unit at the University of Leeds Field Station, and for the supervision of Experiment 1 by Dr. B.J. Clutterbuck.
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