Effect of drought and irrigation on the fate of nitrogen applied to cut permanent grass swards in lysimeters: Leaching losses

Nitrogen losses were measured in water draining from cut permanent grass swards growing in monolith lysimeters containing clay loam (Salop series) or silt loam (Bromyard series) soils. The swards were cut at 6-week intervals during the summer and were fertilised with calcium nitrate at rates of 0 and 400 kg N ha^?1 in each of five successive years (1977–81); in the first year the fertiliser was labelled with ¹⁵N. Four differing rainfall regimes were imposed from spring to autumn in each year. Mean annual losses of nitrogen by leaching from unfertilised swards were 3.8 kg N ha^?1 with mean nitrate-N concentrations in the water of about 1 mg N litre^?1. In fertilised lysimeters where rainfall distribution was that of the long-term average the mean annual total nitrogen losses were 41 kg N ha^?1 in the Salop soil and 15 kg N ha^?1 for the Bromyard soil; mean nitrate-N concentrations were 11.6 mg N litre^?1 and 5.1 mg N litre^?1, respectively. Losses of nitrogen and nitrate concentrations were similar to these quantities when irrigation increased the rainfall total to 120% of average. Where a drought was imposed for 2 weeks before and after each cut, mean nitrate-N concentrations increased to 20.3 mg N litre^?1 on Salop soil and 13.1 mg N litre^?1 on Bromyard soils; total annual nitrogen losses were 74 kg N ha and 33 kg N ha^?1, respectively. The largest losses were recorded when the drought period extended for four weeks before each cut and mean nitrate-N concentrations increases to 28.8 mg N litre^?1 on Salop soil and 34 mg N litre^?1 on Bromyard soil, with total annual nitrogen losses of 104 kg N ha^?1 and 109 kg N ha^?1, respectively. Losses of nitrogen derived from the fertiliser labelled with ¹⁵N were 7.3–8.4% of that applied in the Salop soil (29–33 kg N ha^?1), with little effect by the differing rainfall distributions. On the Bromyard soil, losses were 3.7% (14 kg N ha^?1) of the applied fertiliser in lysimeters not subjected to droughts. When the period of the drought extended before and after each cut, losses were 8.2% (32 kg N ha^?1) and increased to 17.9% (70 kg N ha^?1) when the drought period occurred entirely before each cut. Fertiliser nitrogen contributed 48–69% of the total nitrogen in drainage water from both soils in the first year.     

Effect of drought and irrigation on the fate of nitrogen applied to cut permanent grass swards in lysimeters: Experimental design and crop uptake

The effect of drought and irrigation on the yield and fertiliser nitrogen uptake by cut permanent grass swards was investigated using lysimeters containing monoliths (80 cm diam., 135 cm deep) of two soil types (Salop series, clay loam and Bromyard series, silt loam). Over the five summers 1977–81 swards were treated with four dressings of calcium nitrate at rates of 0 and 100 kg N ha^?1 after each cut; in the first year, the nitrogen was labelled with ¹⁵N. Rainfall equivalent to the long-term average gave mean yields of 12.9 t dry matter ha^?1 for Salop and 14.3 t dry matter ha^?1 for Bromyard. Irrigation (to 120% of average summer rainfall) gave a non-significant increase of 8–9% in herbage yield on both soils. When the average rainfall distribution was modified to create periods of drought for 4 weeks duration immediately before each cut and fertiliser application, yields were significantly depressed, by 12% on Salop soil and 20% on Bromyard soil. Adjustment of the drought so that cutting and nitrogen application fell mid-way in the dry period resulted in only a small non-significant depression of yield on both soils (yield 95–96% of average rainfall treatment). The recovery of applied ¹⁵N labelled fertiliser in herbage during the first year of the experiment was in the range 45–47% for the Salop soil and 39–52% for the Bromyard soil. In the Salop soil the recovery of the labelled nitrogen was not significantly affected by imposition of drought conditions or by irrigation. However, in the Bromyard soil the drought treatment resulted in a significant reduction in the recovery of fertiliser nitrogen to 79% of that of the average rainfall treatment and irrigation increased the recovery to 106%. The contrasting results from the two soils was due to the imposed drought treatments which were more effective in creating differing soil water status in the Bromyard soil. This was due to its good drainage and lower water holding capacity. On both soils, fertiliser nitrogen constituted 53–60% of the total nitrogen content of the herbage. This experiment indicates that on clay soils with poor drainage status, the pattern of rainfall distribution has relatively little impact on the productivity of the sward and its utilisation of fertiliser nitrogen. On freely-draining soils, however, heavy rainfall after drought following cutting and nitrogen application can substantially depress yield and fertiliser use.     

Nitrous oxide emission from permanent grass swards

Emissions of nitrous oxide from permanent grass swards growing on monoliths of clay (Salop series) or silt loam (Bromyard series) soils contained in lysimeters (80 cm diameter, 135 cm deep), were measured between October 1977 and August 1980. With no added fertiliser nitrous oxide emissions were small (equivalent to 10–30 μg N m^?2 h^?1), but after application of nitrate fertiliser (400 kg N ha^?1 year^?1) during the spring and summer months, emissions increased to peak values ca 1000 μg N m^?2 h^?1. The peaks were associated with nitrogen applications and rainfall/irrigation events, but persisted only for 3–7 days. Nitrous oxide production in the soil was mostly restricted to the upper 30 cm of the soil profile. Total annual nitrous oxide losses amounted to 6–8 kg N ha^?1 from the Salop clay soil and 4–6 kg N ha^?1 from the Bromyard silt loam.     

Unused fertiliser nitrogen in arable soils—its contribution to nitrate leaching

Nitrate present in arable soils in autumn is at risk to leaching during the following winter. To see whether unused nitrogen fertiliser was a major source of this nitrate, ¹⁵N-labelled fertiliser was applied to 11 winter wheat crops at rates of between 47 and 234 kg N ha^?1in spring. The experiments were on three contrasting soil types in south-east England. On average, 17′% of the N from spring-applied labelled fertiliser remained in the 0–23 cm soil layer at harvest (range, 7–36%) but only a small proportion was in inorganic forms (ammonium + nitrate). This was never more than 5 kg N ha^?1and averaged only 1·3% of the fertiliser N applied (range, 0·4–3·6 %). Between 79 and 98% of the inorganic N in soils at harvest was unlabelled, being derived from the mineralisation of organic N rather than from unused fertiliser. The amount of unlabelled N was much greater where wheat was grown after ploughing up grass or grass/clover leys than where it was grown in all-arable rotations. When wheat was grown without N fertiliser, soil inorganic N content at harvest was no lower than in plots given fertiliser at rates up to 234 kg N ha^?1. This work indicates that, for soil growing winter wheat, almost all of the nitrate at risk to leaching over the winter period comes from mineralisation of organic N, not from unused fertiliser applied in spring. Consequently, even a drastic reduction in N fertiliser use would have little effect on nitrate leaching.     

The influence of two soil nitrogen levels on the utilisation of 15N-labelled ammonium nitrate by ryegrass

In a field plot experiment with grass under cutting management, two soil organic nitrogen levels (0.92% and 1.14% in the top 75mm of soil) were created by repeated applications of pig slurry over a period of 8 years. The influence of soil organic nitrogen level on the recovery by ryegrass of ammonium nitrate fertiliser was then studied by reseeding the plots and applying ¹⁵N-labelled fertiliser at four rates (40, 80, 120, 160kg N ha^?1). After each of the first four cuts unlabelled ammonium nitrate fertiliser was applied at these same rates. The percentage utilisation of the labelled fertiliser was measured in five harvests over 2 years. At the first cut the percentage utilisation averaged 46.4% and was independent of fertiliser rate and soil organic nitrogen level. The average percentage utilisation values in cuts 2, 3, 4 and 5 were 9.9, 2.4, 0.8 and 0.5 respectively. For the total of all cuts it was only at the 40 kg N ha^?1 fertiliser rate that the percentage utilisation was significantly different (P<0.05) between the 0.92% and 1.14% soil organic nitrogen levels, at 49.0% and 61.4% respectively. The soil nitrogen contribution to ryegrass at the first cut was significantly increased (P<0.05) by the high soil organic nitrogen level at the 40 and 160 kg N ha^?1 fertiliser rates. Over all fertiliser rates the average soil nitrogen contribution to the first cut was 50.4 and 61.1 kg N ha^?1 at the 0.92 and 1.14% soil organic nitrogen levels respectively. From the first cut data, soil organic nitrogen was estimated to have a net mineralisation rate of 2.6% year^?1 and a half-life of 26 years.     

Effects of nitrification inhibitors on uptakes of mineralised nitrogen and on yields of winter cereals grown on sandy soil after ploughing old grassland

An old grass sward on a sandy loam soil (Cottenham series) was ploughed-down in summer 1981 and winter wheat, winter oats and winter wheat respectively were grown on the site for the next 3 years. Nitrification inhibitors (dicyandiamide (DCD), nitrapyrin or etridiazole) were applied to the seedbed in all 3 years. In spring, the cereals were given 0, 35 or 70kg N ha^?1 as “Nitro-Chalk”. Inhibitors had little effect on the amounts or distribution of mineralised nitrogen in the soil profile or on the uptake of mineralised nitrogen during autumn and winter. Much mineralised nitrogen was leached during the autumn and winter 1981/82 and 1982/83, but amounts of available mineralised nitrogen were sufficient to meet the crop requirements. In these 2 years nitrogen fertiliser decreased yields and inhibitors had no consistent effect on yields or nitrogen uptakes. In 1984, winter wheat responded to spring-applied nitrogen fertiliser, while DCD or nitrapyrin increased yields and nitrogen uptakes. There was no evidence that yield increases were due solely to the increased availability of mineralised nitrogen caused by the inhibition of nitrification.     

Effects of husbandry treatments on nitrogen concentration of grain and related yields in winter-wheat experiments made in South-East England

Experiments by Rothamsted staff over 20 years show that N (protein) concentration in wheat grain is influenced considerably by several husbandry treatments other than total fertiliser N. Even small differences can be of practical importance if values lie close to the minimum standard for bread wheat. In 15 experiments which tested timing of fertiliser N, an extra 60 kg ha^?1 would have been needed in autumn to increase grain-N concentration by 0.1% on average, but only 43 kg in early and 30 kg in late spring. The response to autumn N was similar in a ley-arable rotation experiment Fertiliser N applied to a previous potato crop gave a grain-N% increase equivalent to a quarter of the fresh application on a silty clay loam soil but none on a sandy loam. Cumulative annual dressings of farmyard manure benefited grain-N% as did residues from FYM applied to a previous potato crop, which gave increases equivalent to those from 16 kg ha^?1 of fresh fertiliser N. In ley-arable rotation experiments, wheat after arable cropping did not reach bread-quality standard with the largest amount of fertiliser N (150 kg ha^?1), but after lucerne N% values exceeded the threshold value of 2.14% N with all rates. Benefits from lucerne and a grass-clover ley were still considerable when wheat was grown as a second test crop after potatoes. Yield responses to these husbandry treatments tended to be small and positive, except that in the presence of larger dosager of fertiliser N farmyard manure sometimes caused a depression.     

The effect of straw incorporation on the uptake of nitrogen by winter wheat

There was a small decrease in grain yield (from 10.8 to 10.5 t ha^?1) when wheat straw (3 t dry matter ha^?1) was incorporated into a silty clay loam soil sown to winter wheat. In the absence of straw, 60% of autumn-applied ¹⁵N-labelled nitrate was lost from the crop:soil system. Straw incorporation decreased this loss to 47%. There was little overall effect on the uptake of N by the crop, presumably because straw immobilised inorganic N that would otherwise have been leached from the soil during winter. Only 12% of the N in ¹⁵N-labelled straw was recovered by the crop; 78% still remained in the soil one year after incorporation.     

The contribution of fertiliser nitrogen to leachable nitrogen in the UK: A review

Evidence relating to nitrate leaching was taken from series of extensive field experiments conducted to support guidance on fertiliser use. Over the last 50 years, it is estimated that increased fertiliser N use on intensive wheat in the UK, has resulted in an increase of 36 kg N ha^?1 year^?1 leachable nitrate. Probably more than one-third of this change is due to larger yields resulting in a gradual build up in soil organic matter, the remainder to annual effects of fertiliser application. This justifies the association generally made between fertiliser used and nitrate leached and supports the value of some control of fertiliser use in order to restrict nitrate concentrations in drinking water.     

Nitrous oxide emissions from two sites in Southern England during winter 1981/1982

Nitrous oxide fluxes from soil surfaces were measured during winter 1981/82 on two fallow sites, a loamy sand and a clay loam, that had been watered to field capacity and fertilised at the rate of 200 kg N ha^?1 on the 5 October 1981. Highest fluxes were obtained in the sampling period immediately after fertiliser application. They were in the range 3.5–20 g N₂O? N ha^?1 day^?1 on the loamy sand, and declined rapidly from a peak of almost 165 g N₂O? N ha^?1 day^?1 on the day following fertiliser application on the clay loam. The temperature during this period was in the range 6.5 to 14°C. As soil temperature declined during the sampling periods in December (?2 to 3°C) and February (4.5 to 6.5°C) and nitrate was leached in the subsoil, N₂O evolution became very low (<1 g N₂O? N ha^?1 day^?1). Rainfall over the whole sampling period from early October to mid-February was 282 mm. On both sites there was a very high degree of variability within the sites at any sampling time.     

The fertiliser nitrogen requirement of cereals grown on sandy soils

The responses to fertiliser‐N of winter wheat and winter barley grown on sandy soils were measured in 72 experiments in England from 1990 to 1994. Yield without fertiliser‐N (Y₀) was c 1.1 t ha⁻¹ greater following root crops than following cereals. Following potato crops given organic manures, Y₀ was c 1.2 t ha⁻¹ greater than following unmanured potato crops, but Y₀ was no greater following sugarbeet to which organic manures had been applied. Only after the two driest winters was there sufficient variation in soil N supply in spring (SNS_s) for this to show a relationship with Y₀. However, Y₀ increased with increasing N mineralisation during the growing season (AM) in the three years it was measured. There was no consistent effect of sowing date on Y₀. Following potatoes, yield at optimum fertiliser‐N (Y_opt) decreased as sowing date was delayed, but this was not so after cereals, sugarbeet or overall. There was no increase in Y_opt with SNS_S or AM, but Y_opt decreased with increasing moisture stress (S) in June. The mean yield response to N_opt (Δ_Y) was c 0.4 and 0.8 t ha⁻¹ smaller following potatoes and sugarbeet respectively than following cereals, but not consistently so as there were large interactions between site, year and previous crop. Following root crops, Δ_Y was c 0.6 and 1.4 t ha⁻¹ less after sugarbeet and potatoes respectively that had been given organic manures. Without the addition of organic manures, Δ_Y following potatoes was similar to that following cereals. Regression on SNS_S and AM accounted for 28 and 15% respectively of the variance in Δ_Y. The optimum economic fertiliser‐N application (N_opt) was similar, at c 140 kg ha⁻¹, following cereals and potatoes. Following sugarbeet, cereal N_opt was only c 110 kg ha⁻¹. The differences according to previous crop reported here are consistent with mineralisation of crop residues on sandy soils being more rapid than on other soils; the potato residues were rapidly mineralised in autumn and lost by leaching over winter. Residues from later‐harvested sugarbeet were mineralised during the growing season of the subsequent cereal crop. Fertiliser‐N requirements were, at c 110–140 kg ha⁻¹, smaller than has been found on other soil types, and less than current recommendations for wheat. Requirements were significantly reduced in years of drought stress. No differences were found in N_opt between wheat and barley. These data do not justify the current advice to invariably reduce fertiliser‐N to cereals following potatoes by 20–25 kg ha⁻¹ on these sandy soils. On average a reduction of c 20 kg ha⁻¹ could be made following sugarbeet, with a further reduction of c 40 kg ha⁻¹ N if manures had been applied to the previous sugarbeet crop. A reduction of 40 kg ha⁻¹ N could also be made where cereals followed a potato crop to which manures had been applied. Further refinements on the basis of measurements of soil mineral N could not be justified. Seasonal variation in N response due to drought stress makes recommendations difficult on these soils. Adopting the fertiliser‐N recommendations proposed here would produce N surpluses to the soil of c 37, 10 and 27 kg ha⁻¹ respectively following cereals, sugarbeet and potatoes when cereal grain is removed but straw incorporated. On farms where straw is removed, N surplus would be largely eliminated. Our recommendation that no reduction in fertiliser‐N application to cereal crops grown on sandy soils should be made following potatoes will not increase fertiliser‐N use and is not expected to increase nitrate leaching. Some reduction in nitrate leaching may be achieved if recommendations following cereal crops and sugarbeet are made in accordance with the results reported here. © 2000 Society of Chemical Industry     

Quality of white cabbage yield and potential risk of ground water nitrogen pollution,as affected by nitrogen fertilisation and irrigation practices

BACKGROUND: The effect of different fertilisation (broadcast solid NPK application and fertigation with water‐soluble fertiliser) and irrigation practices (sprinkler and drip irrigation) on yield, the nitrate content in cabbage (Brassica oleracea var. capitata L.) and the cabbage N uptake was detected, in order to assess the potential risk for N losses, by cultivation on sandy–loam soil. The N rate applied on the plots was 200 kg N ha^?1. RESULTS: The highest yield (93 t ha^?1) and nitrate content (1256 mg kg^?1 DW) were found with treatments using broadcast fertilisation and sprinkler irrigation. On those plots the negative N balance (?30 kg N ha^?1) was recorded, which comes mainly from the highest crop N uptake (234 kg N ha^?1) indicating the lowest potential for N losses. CONCLUSION: In terms of yield quality and the potential risk for N losses, broadcast fertilisation combined with sprinkler irrigation proved to be the most effective combination among the tested practices under the given experimental conditions. The importance of adequate irrigation is also evident, namely in plots on which 50% drip irrigation was applied, the lowest yield was detected and according to the positive N balance, a higher potential for N losses is expected. Copyright © 2011 Society of Chemical Industry     

Effects of soil management systems and nitrogen fertiliser on the firmness and mean fruit weight of Cox's Orange Pippin apples at harvest

The firmness and mean fruit weight, at harvest, of Cox's Orange Pippin apples from a soil management and N fertiliser trial planted in 1972 were measured from 1979 to 1985 (excluding 1984). Trees growing in overall herbicide, or in 0.3-m herbicide-treated strips with irrigated grassed alleyways, produced significantly softer and/or larger apples than those from trees growing in unirrigated grass with narrow (0.3 m) or wide (1.7 m) herbicide-treated strips in 1982 and 1983. Both these years had drier than average summers. N fertiliser applied annually produced slightly larger and softer apples at 189 kg N ha^?1 than at 63 kg N ha^?1.     

Effects of nitrogen fertiliser on yield,dry matter content and flouriness of potatoes

The effects of incremental amounts of nitrogen fertiliser in the range 0–200 kg ha^?1 on yield ha^?1, tuber dry matter (DM), DM ha^?1and flouriness were evaluated in five potato cultivars over three seasons. In general, yield increased with the use of up to 100–150 kg N ha^?1and remained constant thereafter; % DM of tubers was significantly diminished by amounts of nitrogen > 150 kg ha^?1. In a single poor growing season, yields were small and both yield and% DM were less affected by nitrogen. The mean flouriness score of cooked tubers was highly correlated with specific gravity (SG) class (r = 0.94); tubers with SG > 1.08 were scored floury to very floury. Moderate nitrogen fertiliser use (? 100 kg ha^?1) had little effect on weight per cent of crop > SG 1.08; large amounts of N (200 kg ha^?1) resulted in a substantial decline in the size of this fraction; the effects of intermediate amounts varied with season and cultivar.     

Use of nitrification inhibitors to improve recovery of mineralised nitrogen by winter wheat

Nitrification inhibitors were applied in September 1980, after ploughing of a grass ley, to prevent formation of NO_3-N which could be lost by leaching and denitrification. Laboratory tests indicated that nitrapyrin or etridiazole at 1 μg g soil^?1 and dicyandiamide (DCD) at 10 μg g^?1 could inhibit nitrification by approximately 40%, compared with untreated soil, for 10 weeks at 10°C. In the field, nitrapyrin, etridiazole and DCD had little effect on NH₄ and NO₃ levels in the soil throughout autumn and winter. In April uptake of mineralised N by wheat was greater in plots treated with DCD (but not with nitrapyrin or etridiazole) than in untreated plots. Spring fertiliser N applications (35 or 70 kg N ha^?1) increased ear numbers, as did the two rates of all inhibitors except etridiazole. At harvest, grain and straw yields were increased by both rates of DCD with and without fertiliser N in spring, but there were no consistent increases from nitrapyrin or etridiazole. The mean increases in N uptake by wheat grain plus straw were 12 and 15% for 5 and 20 kg ha^?1 DCD respectively. DCD could be of use in preventing losses of NO₃-N, particularly in situations where large amounts of N may be mineralised during autumn and would be liable to loss prior to crop uptake.     

The nitrogen content of potato (Solanum tuberosum L.) tubers in relation to nitrogen application—the effect on amino acid composition and yields

The effect of nitrogen application on the nitrogen content and yield of amino acids from potato tubers was studied in one experiment in 1983 and two in 1984. Increasing fertiliser N over the range 0–250 kg ha^?1 raised tuber nitrogen concentrations from 0.68–0.81 to 1.27–1.49% DM. Applying half the fertiliser on the seedbed and half at tuber initiation did not increase tuber nitrogen concentrations compared with a single broadcast application at planting. Increasing tuber nitrogen concentrations had little effect upon the proportion recovered in amides or the different amino acids. Yields of some nutritionally essential amino acids were, therefore, substantially increased up to a maximum of 256 kg ha^?1 in 1982 and 308 and 384 kg ha^?1 in 1984 at the highest fertiliser level. These yields were significantly higher (P<0.01) than those found with the nitrogen application rate optimal for tuber dry matter production (213, 195 and 331 kg N ha^?1, respectively) in the same experiments. Methionine and cystine were the limiting essential amino acids. As the amount of each amino acid contained in a unit weight of fresh tuber increased with nitrogen supply, application of more nitrogen than is needed for maximal tuber dry matter production increased protein yields without decreasing the nutritional quality.     

Interacting effects of tillage method,nitrogen fertiliser and secondary drainage on winter wheat production on a calcareous clay soil

The response of winter wheat to nitrogen fertiliser within the range 0–200 kg ha^?1 in 40 kg increments applied either in April or in May in two consecutive seasons (1976–77 and 1977–78) was tested in a field experiment on a calcareous clay soil that was either direct-drilled, shallow tine cultivated (5–8 cm), or mouldboard ploughed (23 cm). These cultivation methods had been used on the same plots in the four preceding seasons (1973 to 1976) in a comparison of cultivation systems. A comparison was also made with direct-drilling on land that had been deep tine cultivated (17 cm) during the 1973–76 experiment. In the second season (1977–78) effects were examined of newly drawn mole drains, on land that had been direct-drilled or ploughed. In both seasons the effect of cultivation method on grain yield was small when nitrogen fertiliser was applied at 80–120 kg N ha^?1. Nitrogen top dressings in April gave heavier yields than the equivalent dressings in May, partly because of dry weather after the May applications in both years. There was no interaction between method of cultivation and amount of nitrogen applied in 1976–77, but a significant interaction was detected in 1977–78 which was probably associated with less nitrogen being available in the uncultivated soil during the winter and spring. The results show that the potential yield of direct-drilled crops may have been underestimated in some earlier comparisons of different methods of cultivation where small uniform top dressings of nitrogen were applied to each cultivation treatment. Mole drainage increased yield especially at low rates of nitrogen and after direct drilling, These results indicate that direct-drilled and ploughed land may differ in their drainage requirements.     

Uptake of foliar-applied urea by winter wheat (Triticum aestivum): The influence of application time and the use of a new 15N technique

A new ¹⁵N technique (termed the negative discard method) for measuring recovery of foliar-applied N by crops in the field is described. ¹⁵N-labelled fertiliser solution is sprayed on to a small area of crop, using a hand sprayer, while the surrounding area is sprayed with unlabelled N at the same rate. An area considerably larger than that given ¹⁵N is harvested with a small-plot combine-harvester, and crop recovery of foliar-applied N is calculated from the ¹⁵N enrichment of the resulting sample containing a mixture of labelled and unlabelled material. The technique was used to measure recovery of N from ¹⁵N-labelled urea solution sprayed on to winter wheat (Triticum aestivum L cv Avalon) at six different times from growth stage 39 (3 weeks before anthesis) to growth stage 73 (2 weeks after anthesis). Each treatment of 40 kg N ha^?1 was divided into two equal portions, the second being applied 1–2 days after the first, to minimise the risk of leaf damage. The crop had earlier received 210 kg N ha^?1, as ‘Nitro-Chalk’, in spring (50 kg ha^?1 at growth stage 22 and 160 kg ha^?1 at growth stage 31) which was more than sufficient to achieve maximum grain yield. At harvest, 70% of the foliar-applied N given at anthesis (growth stage 65) was recovered in the above-ground crop, including 64 % in grain. The proportion of labelled N recovered in the grain (92% of that in the above-ground crop) was slightly greater than with soil-applied N given earlier in the growing season. Recovery of foliar-applied N was slightly less for the earliest (growth stage 39) and latest (growth stage 73) times of spraying: 64% and 58% in above-ground crop, and 56% and 54% in grain, respectively. All of the foliar applications of 40 kg N ha^?1 increased %N in grain to the same extent as an additional 40 kg N ha^?1 applied to soil in spring.     

Reducing gaseous losses of nitrogen from cattle slurry applied to grassland by the use of additives

Losses of nitrogen (N) through ammonia (NH₃) volatilisation and denitrification were determined following the application of cattle slurry to grassland in autumn or spring. Denitrification was examined on two contrasting soils. A system of small wind tunnels was used to measure NH₃ loss and an acetylene inhibition technique for denitrification. Between 31 and 84% of the ammonium N (NH-N) applied in slurry was lost through NH₃ volatilisation. Acidifying the slurry to pH c 5.5 prior to application reduced these losses to between 14 and 57%. On a freely drained loam soil, denitrification from unacidified slurry applied in the autumn at 80 m³ ha^?1 was continuous throughout the winter, with the maximum rate of 0.91 kg N ha^?1 day^?1 occurring a few weeks after slurry application. The total denitrification losses were equivalent to about 29% of the NH-N applied for this treatment and 41% for the acidified slurry. The nitrification inhibitor dicyandiamide reduced the amount of N lost through denitrification by 70% when applied with the slurry at 25 kg ha^?1, by 55% at 20 kg ha^?1 and by 30% at 15 kg ha^?1. The nitrification inhibitor nitrapyrin did not appreciably reduce denitrification. Denitrification losses were consistently small from slurry applied to the freely drained loam soil in spring, or to a poorly drained, silty clay in autumn or spring. Neither nitrification inhibitor was of benefit in these situations.