Soil sampling in autumn gives important information on the soil N dynamic. In the growing seasons 1991/92 to 1995/96, the effects of different crop management systems on soil mineral N (NO3-N plus NH4-N:Nmin) 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, autumn+spring), mineral N fertilization (0, 120 and 240 kg N ha−1) and fungicide application (none, three applications) were all varied. Each year, the treatments occurred in all three crops of the rotation and were located on the same plots. Nmin was determined on four dates (‘After drilling’, ‘End of autumn growth’ before winter, ‘Beginning of spring growth’ before N fertilizer application, and ‘After harvest’) to 90 cm in 30 cm horizons.

Under all crops, Nmin showed a large year to year variation. Highest values of 132 kg N ha−1 were observed ‘After drilling’, which decreased until ‘End of growth’. The increase of autumn Nmin (‘After drilling’, ‘End of autumn growth’) was mainly due to autumn slurry, whereas mineral N fertilizer mainly affected Nmin ‘After harvest’. Soil tillage and fungicide application only slightly modified Nmin at all dates.

The relationship between N leaching and Nmin measured either ‘After drilling’ or at the ‘End of autumn growth’ in 1991/92–1994/95 remained too poor to be used to estimate N leaching. N net mineralization during autumn and winter varied with crops, as estimated by the Nmin changes between ‘After drilling’ minus ‘Start of spring growth’ plus N uptake by the crop at ‘Start of spring growth’ plus N leaching during winter. On average over the years, 39 kg N ha−1 were mineralized under oilseed rape and 42 kg N ha−1 under wheat compared with 31 kg N ha−1 under barley. However, a large year-to-year variation occurred. In addition, the ranking of the years differed with the crops. Slurry application led to different amounts of mineralized N. Under barley only 25 kg N ha−1 were calculated for the autumn slurry, but 42 kg N ha−1 for the autumn plus spring slurry treatment. In contrast, under oilseed rape the highest value of 41 kg N ha−1 occurred in the autumn slurry plots. Under wheat, slurry application only slightly affected N mineralization. Increased mineral N fertilization decreased N release under oilseed rape, but significantly increased it under cereals. Application of fungicides did not affect N mineralization during winter.

A comprehensive study was conducted over a 4-year period (1984–87) to evaluate the water use, growth and yield responses of pearl millet (Pennisetum glaucum (L.) R. Br.) cv. CIVT grown with and without fertilizer (30 kg P2O5 and 45 kg N ha−1) at the ICRISAT Sahelian Centre, Sadoré, Niger. Our study showed significant year and fertilizer effects on the growth and yield of millet at the study site. Observed year effects were primarily due to the variations in the amount and distribution of rainfall in relation to the potential demand for water. During 1984, 1985 and 1987, total rainfall was below the long term average, while in 1986 it was above average. While the onset of rains (relative to the average date of onset) was early from 1984 to 1986, in 1987 the sowings were delayed by as much as 33 days. Of all the four years, the separation between the treatments in the cumulative evaporation is most evident for 1984, which was a drought year with below-average rainfall in all the months from June to September. Cumulative evaporation patterns in 1985 and 1986 were similar because of regular rains and high average rainfall per rainy day from June to October. In 1987, sowings were delayed until 15 July and only 6·9 mm of rainfall was received per rainy day in July. Hence cumulative evaporation was initially low and showed a significant increase only after two significant rain events in early August. There was a large response to fertilizer in all the years as small additions of fertilizer phosphate increased the soluble phosphate in the soil. Fertilizer application resulted in a small increase in water use (7–14%) in all years except 1987. Increased yield due to the application of fertilizer was accompanied by an increase in the water-use efficiency (WUE) in all the four years with the largest increase in 1985. The beneficial effect of fertilizers could be attributed to the rapid early growth of leaves which can contribute to reduction of soil evaporative losses and increased WUE. Over the four seasons, average increase in the WUE due to the addition of fertilizer was 84%.

The potential for using crop wastes as a source of nutrients on the yields of rice grown under submerged conditions was studied in both field and pot experiments at the Experimental Farm of the Agricultural and Food Engineering Department, Indian Institute of Technology, Kharagpur during 1992/93 and 1993/94. The application of groundnut haulm at 3·0 t/ha, maize stover at 5·0 t/ha, mustard stover at 3·0 t/ha and green manure at 1·5 t/ha contributed considerable amounts of nutrients, which improved components of yield, yield and nutrient uptake by rice and also improved the organic carbon (OC) content and available N, P and K in the soil. Yields and soil fertility were both further improved when these organic materials were combined with inorganic fertilizer to supply the recommended amounts of nutrients, except that inorganic fertilizer alone did not cause an increase in the OC content of the soil. In the pot experiment, the production of NH4-N and NO3-N was both larger and more consistent when organic and inorganic nutrient sources were added together than when inorganic sources alone were used.

Swards on wet hill land in mid-Wales, which had been converted from semi-natural rough grazing (dominated by Molinia caerulea, Nardus stricta or Calluna vulgaris) by surface-sowing in the period 1965–75, were examined in 1982, 1984 and 1996/97, using a point quadrat technique, in order to record the extent to which the sown species had persisted and the ingress of unsown species.

Lolium perenne had persisted to 1996/97 to the extent of being 20% of the sward on sites c. 300 m above sea level and 3% on sites at c. 500 m. Trifolium repens had persisted to c. 7% of the sward at both elevations. Festuca rubra was 6% of the sward on the higher sites and close to zero on the lower ones. The other main sown species, Phleum pratense, was present in only trace amounts on all sites in 1982, 1984 and 1996/97. The failure of T. repens to persist in larger amounts was attributed in part to below optimum soil pH and K and to the annual application of fertilizer N. The decline in L. perenne was attributed in part to severe winters on the higher sites and to below optimum soil K and pH. Agrostis spp. were the most prominent of the unsown species. Poa spp. appeared to stabilize at 8–15% of the sward. Stellaria media and Holcus lanatus became fairly prominent on the lower sites and Anthoxanthum odoratum on the higher sites. A supplementary study of the lower sites showed that the lime had been effective to at least the 20–25 cm layer of soil, that the distribution of plant roots in the soil was not abnormal, that T. repens plants had a satisfactory number of root nodules and that the soil contained a satisfactory number of earthworms.

The paper reports a study of the chemical composition of 25400 grass silages produced in England and Wales, of which 1040 were from the period 1961–63, 17900 (15480 clamped and 2420 baled) were from 1982–88 and 6460 (5640 clamped and 820 baled) were from 1992–93. A sample of each silage had been analysed for dry matter (DM), pH, crude protein (CP) and volatile N and in most cases for ash.

The baled silages were drier on average than the clamped silages, with a wider spread of DM contents. The clamped silages with the lowest pH on average were those with a DM content of c. 240 g/kg; clamped silages wetter than this were progressively higher in pH with reduction in DM content; clamped and baled silages drier than 240 g/kg were progressively higher in pH with increase in DM content, up to pH 5·9 in baled silages of 580 g DM/kg. At a given DM content pH was on average 0·6 units higher in baled than in clamped silages. The ash content of baled silages was similar to that of clamped silages. There was an increase in the mean CP content of clamped silages between 1961–63 and 1992–93 and a reduction in the proportion of CP which was volatile. The relationship between DM and volatile N as a proportion of total N was a curve rather than a straight line, with the steepest part of the curve at the lower end of the DM range. The wet silages harvested in 1961–63 were particularly high in volatile N. At a given DM content in the range 170–320 g/kg, volatile N was rather higher in baled than in clamped silages in both 1982–88 and 1992–93. Clamped silages with a DM content of at least 250 g/kg and baled silages with a DM content of at least 310 g/kg were typically well preserved in the sense of having <100 g volatile N/kg total N.

The effects of plant density on the growth and yield of winter oilseed rape (Brassica napus) were examined in a series of five multifactorial experiments at Rothamsted Experimental Station between 1984 and 1989. Plant densities, manipulated by changing the seed rate and row spacing, or because of overwinter losses, ranged from 13·5 to 372 plants/m2. Normalized yields for the multifactorial plots increased with densities up to 50–60 plants/m2. In very high density plots in 1987/88, yield decreased as density increased >150 plants/m2. Plants grown at high density had fewer pod-bearing branches per plant but produced more branches/m2. Branch dry matter (DM) per plant was decreased by 42%, the number of fertile pods per plant and pod DM/plant by 37%. There was no effect of density on the number or DM of pods/m2. Over 74% of the fertile pods were carried on the terminal and uppermost branches of plants grown at high density in 1987/88 compared with only 34% in plants grown at low density in 1988/89. Seed DM/plant decreased with increase in density but seed size (1000-seed weight) increased. There was no effect of density on seed glucosinolate or oil contents.

A field experiment was conducted for 5 years (1992/93–1996/97) on Tolewal sandy loam soil (Typic Ustochrepts) in the subtropical region of northwest India (Ludhiana), to evaluate the effect of four rates of fertilizer P (0, 20, 30 and 40 kg P2O5/ha) applied at three frequencies representing direct, residual and cumulative P treatments on crop yields, P uptake, fertilizer P-use efficiency and fertilizer P recovery by groundnut (Arachis hypogaea) and mustard (Brassica napus) grown in a rotation.

Groundnut responded to an application of P up to 20 kg P2O5/ha when the preceding mustard crop did not receive fertilizer P. However, when the mustard received 40 kg P2O5/ha, the succeeding groundnut crop did not respond to additional P applied to it, but obtained the required P from that which was in the soil including the residue from the previous application. The mustard crop responded significantly (46%) to P up to 40 kg P2O5/ha rate but there was a much less response (13–27%) to residual P that was applied to the preceding groundnut. The differences between these two crops are due to differences in climate between the mustard and groundnut growing seasons and corresponding differences in soil conditions, and perhaps also to differences in the P-solubilizing abilities of the two crops. The results suggest that in groundnut–mustard rotations grown under these climatic conditions, a direct application of 40 kg P2O5/ha to mustard would suffice to meet the P needs of both crops. This would be the most efficient way of using fertilizer P, increasing P recovery and improving total biomass partitioning to mustard seed or groundnut pod yield.

The response of linseed to treatment with two plant growth regulators (PGRs), chlormequat and ethephon, applied at a range of growth stages (corresponding to average mainstem lengths of 10, 23, 46, 55 and 64 cm) and in various combinations (single and repeated applications of chlormequat and ethephon, either alone or mixed) was studied in field experiments over two seasons in 1992 and 1993 at the University College of Wales, Aberystwyth. Reduction in mainstem length was dependent upon the type of PGR and the timing of its application. Chlormequat alone was consistently more effective than ethephon alone, while a mixture of the two at half rates was similar to chlormequat alone. The largest reductions in mainstem length (16·6% with chlormequat and 6·1% with ethephon, averaged over the two years) were achieved when the PGRs were applied when mainstems averaged 22–23 cm in length. Response to PGRs became progressively smaller with later applications. However, the reduction in mainstem length, when expressed as a percentage of that part of the stem yet to extend (i.e. final untreated stem length−stem length at the time of PGR application), was shown to be remarkably consistent across all (apart from the first) timings of application, with average values of 28·4 and 7·4% for chlormequat and ethephon respectively.

Application of both PGRs increased tillering and increased significantly the number of stems per unit area at maturity. This response occurred irrespective of timing of application and was greater following treatment with ethephon than with chlormequat. In the first year, the effects of PGRs on dry matter production and seed yield were small and not statistically significant. In the second year, significant reductions in seed yield were associated with those PGR treatments which promoted tillering most, i.e. early application of ethephon. Smaller yields were the result of fewer capsules per plant. Furthermore, a significant correlation between mainstem length and the number of seeds per capsule indicated a reduction of 0·78 seeds per capsule for every 10 cm reduction in stem length. While total oil content of seed remained unaffected by PGR applications, treatments which included chlormequat at an early growth stage (either alone or in combination with ethephon) altered the relative proportions of fatty acids, reducing the content of linolenic acid while increasing that of oleic acid.

A field experiment was conducted with lemongrass (Cymbopogon flexuosus) at Bangalore, India during 1993–95 under three oil moisture regimes (0·75, 0·50 and 0·25) irrigation water:cumulative pan evaporation (IW:CPE) ratios and four rates of nitrogen application (0, 50, 100 and 150 kg ha−1). The soil moisture regime maintained at 0·75 IW:CPE ratio significantly increased crop growth characters such as plant height, leaf area index, herbage and essential oil yields, compared with those having 0·25 and 0·50 IW:CPE ratios. An application of 100 kg N ha−1 was found to be optimal for crop yield. Oil content and quality of oil were not affected by irrigation and nitrogen rates.

In order to learn more about the feeding value of stovers and straws, seven diets were compared in one experiment and nine in another. The diets in the first experiment were: the upper and lower parts of lucerne (Medicago sativa) hay, the leaves, upper stem and lower stem of maize (Zea mays) stover and the leaves and stem of sorghum (Sorghum vulgare) stover. The diets in the second experiment were: the upper and lower parts of lucerne hay, the leaves, stem and whole stover of millet (Setaria italica), the straw and chaff of wheat (Triticum aestivum), rice (Oryza sativa) straw and sweet potato (Ipomoea batatas) haulm. The diets were fed to sheep to record rate of intake, voluntary intake and in vivo digestibility. The diets were analysed for cell wall (as neutral detergent fibre), crude protein and lignin. Organic matter degradation and cell wall degradation were recorded in nylon bags in the rumen of cattle.

The highest rates of intake (6·8–9·6 g dry matter/min) and voluntary intake (75–103 g dry matter/kg W0·75/day) were with sweet potato haulm and the upper, leafy part of lucerne hay. The voluntary intake of millet leaves, wheat chaff and the lower, stemmy part of lucerne hay was moderately high (46–70 g dry matter/kg W0·75/day). Voluntary intake of leaves was higher than that of stems in the case of millet, sorghum and to a lesser extent maize. The lowest rates of intake were with millet stem, sorghum stem and rice straw (1·8–2·4 g dry matter/min). In vivo digestibility of organic matter was highest (59–67%) for the upper part of lucerne hay, sweet potato haulm, the lower part of maize stem and millet leaves. The leaves of maize were less digestible than the stem, while the reverse was the case with millet. Cell wall content was particularly high (74–78% of dry matter) in millet stem, wheat straw and chaff, rice straw and sorghum stem. Lignin content was low (3·6–4·2% of dry matter) in millet leaves, maize leaves and the upper part of maize stem. Organic matter degradation after 24 h incubation in the rumen was highest (80%) in sweet potato haulm and lowest (39–44%) in millet stem, wheat straw and chaff and rice straw. Cell wall degradation after 96 h in the rumen was highest (76–81%) with the leaves of maize, sorghum and millet and lowest (40–59%) with lucerne hay, millet stem and stover, wheat straw and chaff and rice straw.

Nitrogen (N) inputs and outputs were measured over 3 years in a trial with four farmlets (each with 16 randomly-allocated 0·4 ha paddocks) on permanent white clover/ryegrass pastures which were grazed throughout the year by dairy cows near Hamilton, New Zealand. Three farmlets were stocked at 3·3 cows/ha and received nominal rates of N fertilizer (urea in 8–10 split applications) of 0, 200 or 400 kg N/ha per year. A fourth farmlet with 4·4 cows/ha received 400 kg N/ha per year and was supplemented with maize grain during the first two years.

Nitrogen balances were calculated, with [sum ]N inputs[ape ][sum ]N outputs. Annual inputs from N2 fixation were 99–231 kg N/ha in the 0 N farmlet, but declined to 15–44 kg N/ha in the 400 N farmlets. The main N outputs (in kg N/ha per year) were in milk (72–126), nitrate leaching (20–204), and transfer of N via cow excreta from pastures to lanes and milking shed (54–92). Gaseous losses by denitrification (3–34) and volatilization (15–78) were smaller than the other N outputs but increased significantly with N fertilizer application. In the maize-supplemented farmlet, N outputs in milk were 31% higher than in the corresponding non-supplemented 400 N farmlet, whereas leaching losses averaged 17% lower during the 2 years of supplementation.

In the N-fertilized farmlets, estimated N balances were influenced by inclusion of the transitional N processes of immobilization of fertilizer N into the soil organic N pool (estimated using 15N at 42–94 kg N/ha per year) and the contribution from mineralization of residual clover-fixed N in soil not accounted for in the current estimates of N2 fixation (estimated at up to 70% of measured N2 fixation or 46 kg N/ha per year). However, these processes were counteracting and together were calculated to have only a small net effect on total N balances.

The output of N in products (milk, meat and feed) relative to the total N input averaged 26% in the 400 N farmlets, and is compared to that measured for commercial intensively-managed dairy farms in England and the Netherlands (14–20%). The 0 N farmlet, which was reliant on N2 fixation as the sole N input, was relatively very N-efficient with the milk production being 83% of that in the 400 N farmlet (at 3·3 cows/ha) and the N output in products relative to total N input averaging 52%.

An experiment was conducted in the semi-arid temperate highlands of central Mexico (1994–95) with 12 adult, female non-pregnant, non-lactating, crossbred Nubian goats to determine the effects of 36 weeks of feed restriction on body weight, carcass composition and blood concentrations of glucose and hormones (insulin, triiodothyronine [T3] and tetraiodothyronine [T4]). After a 9-week feed intake, liveweight and body condition stabilization period, the animals were divided into three groups and individually offered either 100, 80 or 60% of their observed average daily consumption. Feed intake was measured daily, liveweight weekly, and blood-serum glucose and hormone concentrations every 4 weeks. At the end of the feeding experiment, the animals were slaughtered, and the carcasses and viscerae weighed. Liver and muscle samples were obtained and chemically analysed. Insulin and T4 did not differ between treatments (P>0·05). Final liveweight; blood-serum glucose and T3; carcass yield; muscle tissue dry matter, fat, RNA and RNA:protein ratios; hepatic tissue protein, RNA:DNA and protein:DNA ratios decreased, while liver and muscle DNA increased with restriction (P<0·05). These results suggest that capacity of goats to adapt to long term undernutrition and the importance of hepatic and muscle tissues as sources of metabolic energy.

The potential use of faecal n-alkanes for estimation of intake and diet composition over periods of 1–2 days was assessed in two experiments. The aim was to determine the accuracy with which intake and diet composition could be estimated by characterizing faecal excretion of n-alkanes following a discrete dose as opposed to steady state kinetics used in previous work.

In the first experiment, 16 sheep were fed mixtures of spinach (rich in C31-alkane) and cabbage (rich in C29-alkane) in known proportions and amounts for two days. Artificial n-alkanes (C28- and C32-alkane) were dosed on four occasions during this time. Total intakes were controlled at 0·2, 0·3, 0·4 or 0·5 kg dry matter (DM) per day and nominal amounts of spinach offered (as a proportion of the total diet) were 0·00, 0·15, 0·30 and 0·45. Each sheep received a unique combination of intake and dietary proportions (four intake rates×four proportions). Sheep were fed fresh grass (timothy, Phleum pratense) before and after feeding spinach and cabbage. Sequential rectal grab samples of faeces were collected at regular intervals and total faecal collections were carried out over 144 h from the start of the spinach/cabbage feeding period to obtain samples for n-alkane analysis. In the second experiment, fresh grass was sprayed with two combinations of artificial n-alkanes (C24- and C32- or C28- and C36-alkane) and fed to 16 sheep over a 24 h period. Each sheep received one of four intake rates (0·8, 1·0, 1·2 or 1·4 kg DM/day) and, within intake rates, each sheep received one of four different proportions of the herbage sprayed with the combinations of n-alkanes (0·2, 0·4, 0·6 or 0·8), in a similar fashion to the first experiment. In order to estimate intake, C26- and C34-alkanes were dosed at the start of the feeding period. Faecal sampling procedures were the same as those in the first experiment.

Different parameters of faecal excretion curves of dosed and natural n-alkanes were used to estimate dietary proportions and intake. Parameters tested included area under the excretion curve and curve maximum. Dietary proportions were calculated using an iterative minimization procedure employing faecal and herbage n-alkane concentrations. Intakes were estimated using ratios of dosed:natural faecal n-alkanes.

The best estimates of dietary proportions were obtained using faecal concentrations at a single point in time in both experiments (>80% variation explained for regressions of estimated v. actual proportions). Intake estimates required the calculation of the area under the excretion curve to obtain acceptable estimates (70–90% variance explained for regressions of estimated v. actual intakes in Expt 2). The experiments demonstrate that precise estimates of diet composition can be obtained using single faecal samples following consumption of simple herbage mixtures over 24–48 h. Intake may also be estimated using this technique provided that a series of faecal samples are collected over 4–5 days following the period of ingestion.