Increasing the efficiency with which crops use supplied nitrogen (N) can minimize the impact on the environment. In the growing seasons 1990/91 to 1992/93, the effects of different cropping systems on yield, N uptake by the grain and apparent N-use efficiency (NUE) of the grain of winter wheat and winter barley were investigated in a factorial field experiment at Hohenschulen Experimental Station near Kiel in NW Germany. The crop rotation was oilseed rape–winter wheat–winter barley, and soil tillage (conservation tillage without ploughing, conventional tillage), application of pig slurry (none, autumn, spring, autumn+spring), mineral N fertilization (0–240 kg N ha−1) and application of fungicides (none, applications against pathogens of the stems, leaves and ears) were all varied. Each year, the treatments were applied to all three crops of the rotation and were located on the same plots.

Averaged over all factors, wheat yield was >7 t ha−1 dry matter in all years and N uptake of the harvested grain varied between 140 and 168 kg N ha−1. Pig slurry application in autumn increased grain yield and N uptake more than spring slurry in two out of three years. Mineral N unfertilized wheat yielded only 5·3–6·3 t ha−1 depending on the year, mineral N fertilization increased wheat yield up to 8 t ha−1. Barley yield was lower than wheat yield, ranging from 4·5 t ha−1 in 1993 to 6·3 t ha−1 in 1992. Unlike wheat, spring slurry N affected barley yield and N uptake more than autumn slurry.

Wheat apparently utilized 12–21% and barley up to 13% of the applied slurry N for its grain development. In 1991, the highest apparent slurry N-use efficiency (SNUE) of wheat and barley occurred after the late spring slurry application. However, in the following years, autumn SNUE of wheat was similar to (1992) or higher than (1993) spring SNUE, presumably because of vigorous tiller growth before winter. Additionally applied mineral fertilizer N decreased SNUE.

Apparent mineral fertilizer N-use efficiency (FNUE) was higher than SNUE and ranged in wheat from 40 to 59% and in barley between 19 and 37% of the applied mineral fertilizer N. FNUE decreased with increasing N fertilization.

To improve the N-use efficiency of both slurry N and mineral fertilizer N, more information is needed about the combined use of both N sources, with special emphasis on split applications of slurry as is common practice for mineral N fertilizer.

Field experiments, conducted during 1992/93 and 1993/94 at the Indian Agricultural Research Institute, New Delhi, indicated that dicyandiamide (DCD) blended with urea produced taller wheat plants with more grains ear−1 and thus higher grain and straw yields than following urea alone. The economic optimum dose (EOD) of nitrogen was estimated to be 73 kg N ha−1 for DCD-blended urea (8[ratio ]2) and 84 kg N ha−1 for urea alone, and the grain kg−1 N of the crop at the EOD was calculated to be 23 kg grain kg−1 N with DCD-blended urea and 18·6 kg grain kg−1 N with urea alone. Thus DCD-blended urea produced more grain using less nitrogen than urea alone. The nitrogen requirement for a targeted yield of 4 t ha−1 was also less when using DCD-blended urea (29 kg N ha−1) than when using urea alone (38 kg N ha−1). The DCD-blended urea resulted in higher N, P and K uptakes, agronomic efficiency and apparent recovery of nitrogen than urea alone.

Amounts of spring nitrogen (N) fertilizer (0–240 kg/ha), combined with three timing treatments (single, divided early or divided late), were tested at 14 sites in England and Wales between 1984 and 1988 to determine the optimum fertilizer N requirement for winter oats. The trials were superimposed on commercial crops of the cultivars Pennal (9 sites) or Peniarth (5 sites). Optimum amounts of N ranged from nil to 202 kg/ha (mean 119) and optimum yields varied between 5·8 and 9·9 t/ha (mean 7·3). Much (c. 60%) of the inter-site variation in N optimum was explained by differences in soil N supply, as indicated by N offtake in the grain at nil applied N. Mean yield differences between single and early (+0·08 t/ha) or late (−0·04 t/ha) divided dressings were slight, although significant (P<0·05) but inconsistent yield effects were obtained from early N at two sites and late N at three sites.

Lodging occurred at 11 of the 12 sites where lodging scores were recorded and always increased significantly (P<0·05) with applied N. The amount of crop lodging at N optimum was, on an area basis, <50% at nine of the sites. The overall extent of site lodging was also influenced by soil N fertility and hence inversely related to N optimum. However, multiple regression, using site lodging as well as soil N supply, only accounted for slightly more (65%) of the variation in N optimum, which suggests that lodging was not a major limiting factor. Lodging was unexpectedly less from early N (mean 43%), but more from late N (53%) divided dressings, compared with a single N dressing (49%). Early N reduced lodging significantly (P<0·05) at four sites, although the actual reduction was only large at one site where early N also increased yield significantly (+0·57 t/ha).

Grain N concentrations increased significantly (P<0·05) with applied N, on average by 0·12% per 40 kg/ha N increment. Timing effects on grain N concentration were very small, with mean values of 1·94, 1·91 and 1·96%N respectively from single, early and late divided dressings. Apparent recovery in grain of fertilizer N at the optimum amount ranged from 13 to 57% (mean 37), with better N recovery at the more yield-responsive sites. Changes in mean grain weight due to the amount and timing of fertilizer N were small, with an average reduction of 0·6 mg/grain per 40 kg/ha N applied. The adverse effects of N fertilizer on grain quality were slight and unlikely to have commercial significance. The agronomic implications of these results on the N fertilization of winter oats are discussed.

In a trial over three successive seasons, the yields of winter barley crops were mapped on a 6 ha field, the soils of which had been mapped according to a system of simple units corresponding to soil series as defined by the Soil Survey of England and Wales. Significant yield variation was explained by differences between soil map units, and the interaction with differences between seasons. The physical properties of the soil series and the potential soil moisture deficits in the three seasons suggested that moisture differences between the soils accounted for much of the observed differences in yield. The implications of these results for crop management in response to within-field variability are discussed.

In parts of peninsular India, sorghum (Sorghum bicolor L.) is grown during the dry season using water stored in the root zone. The optimum application of nitrogen is difficult to assess because no comprehensive model exists for the interaction of water and N. To explore this system as a basis for modelling in the first instance and ultimately for better management, sorghum (cv. SPH–280) was grown in the post-rainy season at ICRISAT (Andhra Pradesh, India) with and without irrigation and at six rates of nitrogen from zero to 150 kg/ha applied before sowing. The biomass of top components was measured weekly and of roots every 2 weeks. Interception of solar radiation was monitored continuously in all treatments.

Leaf expansion was strongly influenced both by water and by N, whereas specific leaf area was almost independent of treatment. In the irrigated treatment, the Biomass Radiation Coefficient (e) for the main growth period was almost independent of N application at 1·3–1·4 g/MJ and was also independent of leaf N. In consequence, the main source of differences in yield was a decrease in radiation interception with decreasing N. In contrast, without irrigation, biomass, yield, e and leaf N were all maximal at 60 kg/ha N.

At 33 days after emergence (DAE), root mass was almost independent of N whether water had been applied or not, but was somewhat smaller with irrigation. Later, root, leaf, and panicle mass all responded to N and to water, but stem mass was unresponsive to N with irrigation. There was evidence of translocation from stem to grain in most treatments. With irrigation, a maximum grain yield of 4·8 t/ha was obtained at 150 kg/ha N and without irrigation the maximum was 3·2 t/ha at 90 kg/ha.

During rainless weather following a monsoon, sorghum (Sorghum bicolor cv. SPH–280) was grown on a Vertisol either unirrigated throughout growth or irrigated for 7 weeks after emergence and rainfed thereafter. Before sowing, ammonium sulphate was applied at six rates from 0 to 150 kg/ha N. Roots were sampled every 2 weeks to determine biomass and root length density as a function of depth. Every week, soil water content in all treatments was measured gravimetrically to a depth of 0·23 m and with a neutron probe from 0·3 to 1·5 m.

Below 0·45 m, volumetric water content was a negative exponential function of time after roots arrived and the maximum depth of extraction moved downwards at 2–5 cm per day. In the dry treatment, the extraction ‘front’ lagged behind the deepest roots by c. 12 days initially but the two fronts eventually converged. Irrigation delayed the descent of the extraction front by c. 20 days but thereafter it appeared to descend faster than without irrigation. Averaged over N rates, the time constant of the exponential function was inversely related to the root length density, lv, decreasing with depth from about 20 to 10 days as lv increased from 2·5 to 4·0 km/m3.

The biomass[ratio ]water ratio was almost independent of N but increased from a mean of 5·3 g dry matter per kg water in the dry treatments to 6·9 g/kg with irrigation. When normalized by the seasonal mean difference in vapour pressure deficit within irrigated and unirrigated plots, the ratios were 13·1 and 13·3 kPa g per kg water, respectively.

In the Sudano-Sahelian zone of West Africa there is potential for groundnut (Arachis hypogaea L.) to be grown as a dry-season crop where irrigation is available. However, there are substantial variations in the temperatures during the post-rainy season that can be expected to influence growth and yield. An experiment at the ICRISAT Sahelian Centre was done in order to study the effect of sowing date on phenology, yield and the processes of yield determination for four groundnut cultivars under irrigation in the dry seasons of 1990/91 and 1991/92. Starting on 15 November, eight sowing dates at 2-weekly intervals were tested. Sowing date significantly affected phenology (time to emergence, flowering and maturity) with groundnut sown in November/December taking the longest time to reach these phenological stages. November and December sowings gave the highest pod yield within each year, despite the lowest crop growth rates (B), and yield declined progressively as sowing occurred later (50% decrease by March) despite increasing B. The observed responses appear to have been due to the effect of temperature differences during the pod-filling phase on partitioning. Partitioning (p) to pods was optimized at c. 30 C, with some indication of cultivar differences in partitioning response to temperature. Across all the environments, cultivars displayed substantial differences in yield stability. When sown late, yields were low and lines with high partitioning were the best. When sown early in the post-rainy season, cultivars with a high B value were the better choices. Plant habit differences and B suggest that radiation interception was a limitation to yield, particularly when the crops were sown in the cool months of the year. However, haulm yield and crop growth rates were not consistently affected by sowing date across the years, and cultivars demonstrated different degrees of stability for B. It is concluded that where pod has a price advantage over fodder, irrigated groundnut for the dry season should be sown in November to allow the crop to develop under the relatively cool temperatures that maximize pod yield. Further agronomic research is suggested to maximize B for individual cultivars for given sowing dates.

Experiments to evaluate the optimum plant population density and sowing date for winter peas, semi-leafless cv. Rafale, were sited on free draining sandy loam soils at Thornhaugh, Cambridgeshire in 1993/94 (Expt 1), 1994/95 (Expt 2) and 1995/96 (Expt 3). Peas were sown at the end of October, in mid-November and early December, at seed rates to achieve final plant densities in spring of 50, 70 or 90 plants/m2. Seed rates were calculated allowing for 20% seedbed loss and plant loss due to winter kill in Expt 1, and 15% in the other two years.

Peas sown in warmer seedbeds in October emerged in early December or before, November-sown peas did not emerge until mid-January and December-sown peas from late February to mid-March. The growth stage of October-sown peas was thus more advanced than the later sowings over the winter and spring period. Winters were mild for Expts 1 and 2, but there were more frost periods during Expt 3.

The yield of winter peas was dependent on sowing date. Yields of Rafale sown in October were highest in Expt 1, but lower than November-sown peas in 1995 (Expt 2), as a result of damage from late frosts during flower initiation in April, and in 1996 (Expt 3) due to plant losses after a more severe winter, frost periods and very cold winds in March. In Expts 1 and 2, yields of December-sown peas were significantly lower than November-sown peas, probably because they were adversely affected by drought stress during the sensitive flowering period. Therefore the optimum time for sowing winter pea cv. Rafale to achieve reliable yields appears to be mid-November. In some years, however, conditions may be too wet for late drilling, particularly on heavier soils.

The highest plant population densities of 90 plants/m2 gave the highest yields in Expts 2 and 3, but there was little increase between 75 and 90 plants/m2. Bearing in mind financial return and seed costs, the optimum target suggested is 75–80 plants/m2.

Lime loss rates were determined for 11 agricultural soils across England (1987–92) under arable cropping (six sites) and grassland management (five sites), receiving commercial rates of fertilizer inputs. Lime additions in the range 0–1500 kg ha−1 CaCO3 (250 kg ha−1 CaCO3 increments) were made annually to the sites. Soil pH (water and 0·01 m CaCl2) and exchangeable calcium concentrations were measured annually. The annual lime loss rates were calculated as the amount of lime needed to maintain the initial site pH or exchangeable Ca concentrations.

Lime loss rates based on soil water pH varied between 40 and 1270 kg ha−1 CaCO3, on the basis of CaCl2 pH between 0 and 1370 kg ha−1 CaCO3, and exchangeable Ca between 0 and 1540 kg ha−1 CaCO3. There was a positive relationship between the lime loss rate (based on water pH) and initial soil pH value (r=0·75; P<0·01), and a negative relationship with soil organic matter content (r=0·63; P<0·05) was based on soil pH, organic matter content and nitrogen (N) fertilizer input. Lime loss rates were approximately double those predicted by previous models developed in the 1970s, reflecting the greater quantities of inorganic N fertilizer now being applied to agricultural land.

It is possible to estimate diet composition from an analysis of n-alkanes in the faeces of ruminant animals. The method requires the estimation of the concentrations of n-alkanes in the plants and faeces and then the solving of a system of simultaneous equations. There are at least three places in which significant measurement error may be introduced. First, there may be error in the determination of the concentrations of the n-alkanes in the herbage. This error may be the result of analytical error in the chemical analysis, or in the gathering of the representative sample of herbage. In either case, error in this estimate may be particularly important, since this estimate is not independently repeated for each animal in the study, but is conducted once and used throughout the study. Error may also be introduced in the estimates of digestibility of the n-alkanes themselves. The n-alkane method might be ideal if in fact the n-alkanes were completely indigestible – they are not and, furthermore, they are differentially digestible. Lastly, there may be measurement error in the estimate of the n-alkane concentrations in the faeces, which utilize the same analytical procedures that are used on the herbage. That is, if measurement error exists in the herbage estimates, it is quite possible that it also exists in the faeces estimates. We address these issues through the use of Monte Carlo simulation to investigate the likely effects of measurement error on diet composition and digestibility estimates obtained using the n-alkane method. Our results suggest the following conclusions: (1) in the face of any sort of measurement error, estimates of digestibility are likely to be unreliable; (2) when measurement error exists, one of the diet components will usually be under-estimated and the other will usually be over-estimated; (3) any sort of progressive bias in the n-alkane recovery estimates will probably have large and very significant effects on the results; and (4) if measurement error in the estimates of the n-alkane concentrations in the herbage and in the faeces are similar in expectation, then their effects tend to cancel each other out.

Metabolizable energy intake and heat production were measured in a series of calorimetry experiments carried out at the Agricultural Research Institute of Northern Ireland, Hillsborough, between 1993 and 1996 with beef cattle and sheep. A total of 75 estimates were made with cattle: 23 with Charolais cross steers; 16 with Simmental cross steers and 36 with Angus cross steers (450–628 kg liveweight). Fifty-six estimates were made with lambs: 24 with Blackface cross, eight with Suffolk cross and 24 with Texel cross (23–53 kg liveweight). The diets offered to both cattle and sheep contained proportionately 0·0–0·8 cereal-based concentrates, the remainder being grass silage. Linear regressions of energy retention (measured by calorimetry) against metabolizable energy intake were produced for the cattle and sheep studies. From these linear regressions an estimate of metabolizable energy required for maintenance (MEm) was obtained. For cattle, the derived MEm was 0·614 MJ/kg LW0·75 per day, and for sheep the derived MEm was 0·460 MJ/kg LW/kg LW0·75 per day. The estimates were proportionately 0·34 higher in cattle and 0·32 higher in sheep than the 1990 values of the UK Agricultural and Food Research Council.

Of 41 male kids, 14 were killed immediately after birth (3·3 kg BW); the remainder were either fed on goat milk to satiation or weaned at 10 kg BW. After achieving 15·7 kg BW, weaned kids were fed on complete diets including either 20 or 40% straw. Milk-fed kids were slaughtered at 16·8 or 26·7 kg BW, weaned kids at 15·7 or 29–30 kg BW, respectively (at least four kids per treatment). Empty BW as a proportion of final live BW was 0·91±0·02 in milk-fed kids compared to 0·85±0·04 and 0·76±0·04 in kids given complete feeds including 20 or 40% straw, respectively. Empty BW of kids in the heaviest groups were c. 24 kg for milk-fed or weaned kids. Energy and crude protein contents per kg empty BW increased from 4·5 MJ and 158 g in newborn kids to 12·2 MJ and 163 g in milk-fed kids or 10·4 MJ and 194 g in weaned kids, respectively. No influence of the feeding system was found on mineral contents of empty BW. Ca, P and K remained constant at 12·6, 7·7 and 1·9 g/kg, Mg increased from 0·32 to 0·46 g/kg and Na decreased from 2·0 to 1·3 g/kg. Differences in composition of live BW gain are mainly caused by differences in gut-fill. Efficiency of utilization of ME for growth was c. 0·75 in milk-fed kids even at high BW, but only 0·31 in weaned kids. Proportions retained of dietary N, Ca, P, Mg, Na and K were highest in milk-fed kids between birth and 16·8 kg BW: 0·57, 0·88, 0·78, 0·40, 0·37 and 0·10, respectively. They were lowest in kids fed on complete feed including 40% straw from 15·7 to 30·3 kg BW: 0·25, 0·26, 0·32, 0·04, 0·11 and 0·04, respectively. Weaning seems to be of greater influence on composition of BW gain and efficiency of utilization than the increase in empty BW.