ALBERT

Description: SUMMARYAn earlier report of leaf scorch and diminished yield when using large amounts of urea on winter oilseed rape (Brassica napus) was investigated by applying 200 kg N/ha as calcium ammonium nitrate (‘Nitro-chalk’) or urea as a single dressing or divided in six ways. The ‘single-low’ variety Mikado (low in erucic acid) was grown in 1986 and was compared with the ‘double-low’ variety Ariana (low in erucic acid and glucosinolates) in 1987 and 1988. No scorch was seen in these experiments. Yield from rape fertilized with prilled urea was, on average, 98% of that from rape fertilized with ammonium nitrate. The timing and distribution of the fertilizer also had little effect on yield, though yield slightly decreased when part of the dressing was withheld during March. The earlier-maturing variety Mikado always outyielded Ariana except when harvest was delayed by bad weather.When plots were fertilized with urea, the oil content of the seed was a little larger than when fertilized with Nitro-chalk, which compensated for the smaller seed yield, resulting in almost equal oil yield from both forms of N fertilizer. Crude protein content was lower after a large single dose of urea fertilizer but parity with ammonium nitrate was restored by smaller amounts applied on a number of occasions. Neither form nor timing of N fertilizer had any consistent effect on the total glucosinolate content.The incidence of disease was significantly greater in rape given either form of N fertilizer than where none was given, but when downy mildew (Peronospora parasitica) was prevalent on pods there was significantly less infection in plots fertilized with urea than with ammonium nitrate.

Description: SUMMARYThe effects on a winter wheat test crop of a preliminary year of winter or spring field beans (Vicia faba), winter oats, winter oilseed rape, winter or spring peas (Pisum sativum), winter wheat, spring lupins (Lupinus albus), spring sunflowers (Helianthus annuus) or a cultivated fallow were compared in three 2-year experiments on clay-with-flints soil at Rothamsted from 1986 to 1989. In one experiment, autumn-sown ryegrass (Lolium perenne) and an uncultivated fallow, given weedkiller, were also included in the first year. Plots of test-crop wheat were divided to compare no N fertilizer with an optimal amount estimated from a predictive model.Amounts of take-all (Gaeumannomyces graminis) in the test crop of wheat following wheat were very slight in the first experiment, but large in the second and third. All the break crops reduced takeall to none or very slight amounts.Amounts of NO3-N in the soil in autumn after the first-year crops ranged from 7 to 95 kg N/ha. On average, they were least after oats, and most after cultivated fallow. In autumn 1988they were least after autumn-sown ryegrass. In early spring, amounts of NO3-N were generally less, ranging from 7 to 55 kg N/ha, depending on preceding crops, sowing date of the wheat and the weather. Amounts of NH4-N in soil were little affected by preceding crops or weather and were generally smaller in spring.The estimated average N fertilizer requirement of test-crop wheat following winter wheat was 230kg N/ha. This was increased by 10 kg N/ha following winter oats, decreased by 40 kg N/ha after spring peas and by 30 kg N/ha after winter rape, winter peas, spring beans and cultivated fallow. Other preliminary crops not represented every year had effects within this range.Grain yields of test-crop wheat given optimal N averaged 7·2 t/ha after winter wheat, c.1·5 t/ha less than the average after most of the break crops. The yield after oats was limited by self-sown ‘volunteers’ and that after ryegrass by limited soil N after ploughing.Of the break crops tested, winter and spring beans, winter oats, winter rape and spring peas all gave satisfactory yields. A farmer should choose between these on the basis of local farm circumstances and current economics of the break crops. Differences between effects on take-all and savings on fertilizer N were too small to influence this decision.

Description: SUMMARYOptimum applications of N fertilizer, Nopt have been related successfully to the amount of mineral N in the soil, Nmin in some parts of Europe but not always in the UK. If there is a body of mineral N, QN, that ultimately lessens the need for N fertilizer, it will not remain constant in its amount or its position. Mineralization will add to QN, while the nitrate component of QN will be leached downwards.Also, part of QN will be taken up into the crop where it will continue to lessen the need for fertilizer N but will be safe from leaching. A computer model was used to simulate these processes for 23 experiments, covering five sites and five years, in which N opt had been estimated. From these simulations we derived trial values of QN that took account of mineral N to a series of depths on a series of dates. For each date we used the trial values to find the depth for which Nopt was best correlated with QN andassumed that this was the depth, dL, of the lower boundary of QN on that date. Thus dL was a collective value for all 23 experiments. The value of dLincreased throughout the winter and the spring and was very closely related to the cumulative average drainage through 0·5 m soil at Rothamsted. By 15 April, dL, was 1·66 m, a depth that was compatible with observations by others that winter wheat can remove mineral N to a depth of at least 1·5 m. We inferred two likely reasons why Nmin may fail as a predictor of Nopt in the UK: insufficient depth of sampling, and too wide a spread of sampling dates. The values of Nopt were shown to be related satisfactorily to the values of QN computed, without any measurements of mineral N, for appropriate depths on single dates.

Description: SUMMARYMultifactorial experiments at Rothamsted Experimental Station in two contrasting seasons, 1985/86 and 1986/87, tested the effects of treatment combinations that varied the supply of nitrogen at important stages of crop development in autumn and spring on the grain yield and nitrogen content of September- and October-sown winter wheat. Treatments that altered the nitrogen supply in autumn were an application of winter fertilizer N and sowing the wheat after rape or oats, which left different amounts of residual N. These were combined with treatments which tested the effects of 200 kg N/ha in spring applied as early or late dressings and as single or divided dressings. The effect of applying an additional 50 kg N/ha in summer was also tested in 1985/86.In both experiments, larger yields were obtained from sowing in September than in October. The September-sown wheat grew better over winter in 1986/87 than in 1985/86 but the early advantage in size and N uptake resulted in enhanced production of straw rather than grain. Residues of N from previous crops were smaller after oats than rape in both years. This difference in soil N did not affect the over-winter growth and N uptake of the October-sown wheats. Neither this difference in residual N nor an application of fertilizer N in winter affected the yield of the following September-sown wheat in 1985/86 because autumn growth and N uptake were restricted by adverse weather. In 1986/87, however, wheat that followed oats yielded 0·42 t/ha less grain than wheat that followed rape, and the deficit in yield was removed by an application of fertilizer N equivalent to the deficit in soil N.Yields were decreased when the spring N was applied as a delayed, single dressing in April especially if the wheat was sown in September after oats, or was not given winter N. Yields were not affected by any of the other combinations of single v. divided dressings or early v. late applications of spring N, despite these being given at very different stages of apical development.The percentage of N in the harvested grain was greatly increased by winter applications of fertilizer N, especially to wheat grown after oats, by applying the spring N as a late, single dressing and, in 1986, by applying N in summer.

Description: SUMMARYEffects of agronomic factors on yield of winter oilseed rape were examined in multifactorial experiments, with a single-low (low erucic acid, high glucosinolate) cultivar (Bienvenu) in 1984/85 to 1987/88 and a double-low (low erucic acid, low glucosinolate) cultivar (Ariana) in 1986/87 to 1988/89. Establishment of September-sown plots was better than that of August-sown plots in 1984, 1987 and 1988, but not in 1985 when September was very dry. The total dry matter (DM) (kg/ha) of August-sown plots was much greater than that of September-sown plots throughout autumn and winter but by harvest the plant DM of late-sown plots was slightly greater. Combine-harvested yields of late-sown plots were greater than those of early-sown plots in 1984/85 (cv. Bienvenu) but not in 1988/89 (cv. Ariana); effects of sowing date on yields were smaller in other seasons, although late-sown plots generally had larger yields. Insecticide treatments increased combine-harvested yields in 1987/88 (cv. Bienvenu) and 1988/89 (cv. Ariana) and increased hand-harvested yields in 1984/85, by increasing the number of plants/m2. Fungicide spray treatments increased yields in all years except 1989, by increasing 1000-seed weights. Application of growth regulator sprays increased yields in 1986/87 to 1988/89; effects on cv. Ariana were associated with increased numbers of pods/plant. There were no consistent effects of spring nitrogen rates or timing on yield or yield components.

Description: SUMMARYIn the first of two series of experiments the effects of barley straw disposal by burning, chopping and spreading or baling and removing on winter oilseed rape were tested after seedbed preparation either by ploughing in the residue or incorporation in the soil by tine cultivation. These treatments were compared in four field experiments on silty clay loam soils at Rothamsted, UK from 1986 to 1989. The winter rape was either sown in late August or mid-September in seedbeds where either none or 50 kg N/ha had been applied.In the first season, August-sown rape was successfully established after tine cultivation but very dry conditions prevented seedbed preparation after ploughing, consequently all ploughed treatments were sown in September. Continuing dry conditions delayed emergence of the September-sown crop, the resultant small rape seedlings suffered substantial winter kill in some treatments during a period of abnormally low temperatures. Yield from the August-sown treatments was large (c. 40 t/ha) and showed no effect of straw disposal treatment or additional seedbed N. The yield of the September-sown crop was influenced by the amount of winter kill sustained; the smallest yields resulted from tine incorporation, and the largest after ploughing, where they approached those of the early sown crop.In the following three seasons more plants emerged from September than from August sowings. The application of seedbed N increased the plant population of the August-sown crop where the straw had been burnt. Plant losses over winter ranged from 15 to 20% and were unaffected by straw disposal treatment. There were significant differences in yield resulting from season and sowing date. Incorporating chopped straw by tine cultivation significantly decreased yield which, coupled with a lower oil content in the September-sown crop, gave a significantly smaller oil yield.In a second series of field experiments from 1987 to 1989, the effects of improving the timeliness of rape establishment after winter wheat by broadcasting rape seed into standing wheat was compared with conventional sowing after preparing a post-harvest seedbed. After cereal harvest, straw was disposed of either by baling and removing or chopping and spreading over the rape seed. The application of 50 kg N/ha to the stubble or seedbed was also tested, as was the effect of increasing the seed rate from 8 to 16 kg/ha in two seasons.There were always fewer plants established from broadcasting than from drilling. Generally there were fewer winter losses from broadcast seed than from drilled. Applying N to seedbed or stubble had no effect on plant population or survival except where 16 kg/ha seed was sown in 1989 and increased yield in two of the three seasons.In spite of a smaller plant population from broadcast seed, yields were often larger from broadcast than drilled treatments. On average broadcasting the seed and baling the straw gave the largest yield although this was significant only in 1989.

Description: SUMMARYIn experiments at Rothamsted in 1984–86, seven factors, each at two levels, were tested in factorial combination on winter barley (cv. Panda) grown as a third take-all susceptible crop. The factors were seed rate, a growth regulator prior to stem extension, amounts of N in spring, ‘winter’ nitrogen, an autumn insecticide, a fungicide applied to the seed (‘Baytan’) and a programme of fungicide sprays in spring and summer. Sowing 50% more seeds than normal increased the number of ears/unit area but had no effect on mean grain yield because grains were smaller. There were, however, significant, but unexplained, interactions between seed rate and the fungicide ‘Baytan’ applied to the seed. A growth regulator applied prior to stem extension had little effect on crop growth and no significant effect on grain yield. If sufficient N was applied in April there was little benefit from applying ‘winter’ N (30 kg/ha in November and again in February/March) except in 1985 when the amount of NO3-N in the soil, measured in the previous October, was lowest. Insecticide sprays applied in autumn to control the aphid vectors of barley yellow dwarf virus (BYDV) had no significant effect on grain yield but infectivity indices were below the threshold needed for treatment in each year. On average, ‘Baytan’ applied to the seed increased grain yield by 0·28 t/ha and this was associated with decreases in the severity of take-all. Over the three years, programmes of fungicide sprays, applied during spring and summer, increased grain yield by 0·92 t/ha but the mean response was largest where most N was applied.The experiments also allowed the importance of interactions between different agronomic factors to be examined. A combined analysis of grain yields for all three years (based on 192 plot values) showed that only six 2- or 3-factor interactions, out of the 73 estimated, were significant (P 〈 0·05). Two of these interactions reflected variable responses to ‘winter’ N and fungicide sprays in the three years and three of the remaining four involved ‘Baytan’.Additional plots of barley grown after oats had little take-all and yielded 1·14 t/ha more grain than similarly treated plots grown after barley. These responses were obtained despite evidence that oat residues had adverse effects on the growth of barley seedlings. Additional plots of barley grown after a bare fallow also had little take-all and gave even larger total yields (grain plus straw) than did barley after oats but the mean yield of grain was less than after oats because more of the dry matter after a fallow was straw. In 1984, when take-all was relatively slight, plots after a fallow gave even less grain than plots after barley (−0·77 t/ha) despite producing 2·12 t/ha more dry matter in grain plus straw.