Experiments in three dry seasons (1993/94, 1994/95, 1995/96) on a loamy medium sand at ADAS Gleadthorpe, Nottinghamshire, England tested responses of green area, radiation interception, water uptake and above-ground dry matter growth of six wheat cultivars to irrigation. Cultivars differing in date of introduction (Haven 1987, Maris Huntsman 1969, Mercia 1983, Rialto 1991, Riband 1985 and Soissons 1989) were chosen for contrast in flowering time and maximum green area. Maximum soil moisture deficit (SMD) exceeded 140 mm in all years, with large deficits (> 75 mm) from early June in 1994 and more prolonged large deficits in 1995 and 1996. Restricted water availability first affected canopy expansion at a SMD of 74 mm (50% available water capacity; AW), and canopy senescence at 95 mm (64% AW). Decreases in biomass at harvest were larger with prolonged droughts in 1995 and 1996 (424–562 g/m2) than in 1994 (222 g/m2). Compared in the two driest years, 1995 and 1996, the decrease in biomass was greater in Haven (599 g/m2) than in Maris Huntsman (420 g/m2) (P < 0·05). The better drought resistance of Maris Huntsman appeared to arise through its greater water use efficiency (WUE); 6·2 cf. 5·5–5·7 g/m2/mm. The susceptibility of Haven to drought was possibly due to restricted water uptake, depression of radiation use efficiency (RUE) and accelerated senescence. The cultivars differed in flowering by up to 9 days but date of flowering correlated poorly with biomass response to irrigation. Early flowering was, however, correlated with favourable distribution of seasonal water use with respect to the grain filling period. The maximum green area index (GAI) of cultivars varied from 4·4 to 5·3 (P < 0·01), but differences were countered by shifts in the extinction coefficient (K), such that season-long radiation interception varied little. Green area index maxima did not therefore relate to the pattern of growth or water use, and they were correlated poorly with the biomass responses. Cultivars did not differ in their maximum depth of water extraction; they all extracted water to 1·65 m depth in each year. It is concluded that early flowering and high WUE might offer scope for improving drought resistance in the UK's temperate climate, but that small maximum GAI seems less useful.

This study was established to quantify the uptake of 15N-labelled nitrogen (urea) applied in the first and second years of perennial ryegrass (Lolium perenne L.), tall fescue (Festuca arundinacea Schreb.) and browntop (Agrostis capillaris L.) seed crops, and the availability of the residual fertilizer N to a subsequent wheat (Triticum aestivum L.) crop under field conditions in Canterbury, New Zealand. Total recovery of 15N-labelled nitrogen fertilizer was approximately 100% when fertilizer was applied to the grass seed crops in spring. At harvest in year 1, grass straw and seed contained 34–47% and 6–15% of the applied N respectively; 27–35% remained in the soil (0–150 mm depth). Recovery of 15N in straw and soil was higher in fescue and ryegrass than in browntop, but recovery in roots was lower. At harvest in year 2, most of the 15N was present in the soil (30–37%) with only small amounts in the seed (0·7–1·0%), straw (3·6–4·9%) and roots (5·2–12·7%). In year 3, 2·5–3·5% of the residual 15N was recovered in the wheat and 18–26% in soil. Losses of 15N were minimal until ploughing after the second harvest, when there was an apparent loss of 11–35% of the fertilizer N applied. Losses were not directly associated with the fertilizer but indirectly following release of fertilizer N previously immobilized in plant roots and soil microorganisms. Small losses also occurred directly from autumn-applied N, probably through leaching. Despite these losses, overall there was an accumulation of fertilizer N in the soil organic pool, suggesting that ryegrass fescue and browntop seed crops have a role in contributing to the N fertility of the soil.

Forty-three near-isogenic lines (NILs) of white clover (Trifolium repens), derived from four parental self-compatible genotypes containing the rare self-fertility allele, were inoculated with the arbuscular mycorrhizal fungus Glomus mossae. Plant growth response (shoot and root weight and root length), shoot P uptake and mycorrhizal root infection rates were recorded 12 weeks after inoculation. There was generally a high degree of variation between individual lines in all recorded parameters. The most sensitive indicator of plant response to mycorrhizal infection was root length with almost half of all lines showing significant responses (in most cases a decrease in root length). Shoot weight was significantly different between mycorrhizal and nonmycorrhizal plants in nine lines. Parental genotype significantly affected both plant response to mycorrhiza as well as mycorrhizal infection rates. The results suggest that the NILs will prove useful for further studies to elucidate the molecular genetic control of the symbiosis and inform plant breeding strategies of this agronomically important species.

The aim of this study was to select the best arrangements of MP–PCR (microsatellite-primed PCR) for routine large-scale fingerprinting of flax cultivars. We found optimum PCR conditions for the application of five previously published primers (PCT1–PCT5) to flax cultivar fingerprinting. We modified to optimum MP–PCR which was targeted to flax tetrameric [GATA] microsatellite loci specified by primer PCT6. We found that after a reamplification PCR step was involved we were able to generate highly discriminating fingerprinting patterns, which distinguished all eight flax cultivars individually. In particular primers 3PCT1 and 3PCT2 were promising for future large-scale fingerprinting due to the production of most polymorphic bands. Increasing annealing temperature within a temperature profile helped to generate new polymorphisms within flax microsatellite patterns especially with primer 3PCT2. Using this primer we succeeded in generating new polymorphic bands after increasing annealing temperature from 55 °C to 60 °C, and to 65 °C. A cluster analysis of flax cultivars was performed based on microsatellite data. The core group of eight flax cultivars was clustered into two homogeneous subclusters. A lower level of cultivar clustering within subclusters was not detected.

Low organic matter concentration coupled with low native soil phosphorus (P) concentrations is a major constraint limiting the productivity of a soybean–wheat system on Vertisols in the Indian semi-arid tropics. In a 3-year field study (1996–99), the performance of four different composts obtained from legume straw (Glycine max Merr.L), cereal straw (Triticum aestivum), oilseed straw (Brassica juncea L.) and city rubbish were compared, and also with chemical fertilizers in terms of degree of maturity, quality of compost, improvement in soil organic matter, biological activities of soil and yields of soybean and wheat. Phospho-sulpho-nitrocomposts (phosphocomposts) were prepared containing approximately 2·5 to 4·2% P and 1·4 to 2·3% N, in an aerobic decomposition process for 4 months by adding an aqueous slurry of 1:1 (dry weight) cow dung, 2·2% P in the form of low grade Mussorie phosphate rock (7·5% P), 10% pyrite (S, 22·2%) and 0·5% urea N, and bioinoculums such as the cellulose decomposers Paecilomyces fusisporus and Aspergillus awamori, and P-solubilizing organisms i.e. Bacillus polymyxa and Pseudomonas striata. The maturity indexes were strongly associated with the source of materials, chemical composition and degree of decomposition. The matured composts had lower C/N ratios (8·2 to 21·7) and water soluble carbohydrates (0·23 to 0·43%) and larger ratios of cation exchange capacity/total organic carbon (CEC/TOC) and lignin/cellulose than the initial. The matured compost increased total P, water soluble P, citrate soluble P, total N and NO3-N and the application of phosphocompost at the rate of 10 t/ha gave plant growth dry matter accumulation, seed yield and P uptake by soybean equivalent to single superphosphate at 26·2 kg P/ha. The continuous turnover of enriched phosphocompost increased soil microbial biomass C and the activity of enzymes compared to application of chemical fertilizer.

HRI WELL_N is an easy to use computer model, which has been used by farmers and growers since 1994 to predict crop nitrogen (N) requirements for a wide range of agricultural and horticultural crops.

A sensitivity analysis was carried out to investigate the model predictions of the N fertilizer requirement of cauliflower crops, and, at that rate, the yield achieved, yield response to the fertilizer applied, N uptake, NO3-N leaching below 30 and 90 cm and mineral N at harvest. The sensitivity to four input factors – soil mineral N before planting, mineralization rate of soil organic matter, expected yield and duration of growth – was assessed. Values of these were chosen to cover ranges between 40% and 160% of values typical for field crops of cauliflowers grown in East Anglia. The assessments were made for three soils – sand, sandy loam and silt – and three rainfall scenarios – an average year and years with 144% or 56% of average rainfall during the growing season. The sensitivity of each output variable to each of the input factors (and interactions between them) was assessed using a unique ‘sequential' analysis of variance approach developed as part of this research project.

The most significant factors affecting N fertilizer requirement across all soil types/rainfall amounts were soil mineral N before planting and expected yield. N requirement increased with increasing yield expectation, and decreased with increasing amounts of soil mineral N before planting. The responses to soil mineral N were much greater when higher yields were expected. Retention of N in the rooting zone was predicted to be poor on light soils in the wettest conditions suggesting that to maximize N use, plants needed to grow rapidly and have reasonable yield potential.

Assessment of the potential impacts of errors in the values of the input factors indicated that poor estimation of, in particular, yield expectation and soil mineral N before planting could lead to either yield loss or an increased level of potentially leachable soil mineral N at harvest.

The research demonstrates the benefits of using computer simulation models to quantify the main factors for which information is needed in order to provide robust N fertilizer recommendations.

A study was conducted on a 15×15 diallel set of tomato excluding reciprocals to find out the extent of heterosis, combining ability and nature of gene action for yield with two important quality traits: ascorbic acid (vitamin C) and total soluble solids (TSS). Significant differences among genotypes were obtained for all three traits. Positive high significant heterosis was found for yield (41·97, 157·84 and 28·94%), for ascorbic acid (16·68, 54·57 and 161·33%) and for TSS (25·97, 11·93 and 19·02) over the top, the better parent and the commercial control respectively. The magnitude of variance due to general as well as specific combining ability were highly significant indicating the importance of both additive and non-additive gene action. However degree of dominance (o−2 g/o−2 s) revealed the prevalence of a non-additive gene effect. Cross combinations Arka Vikas×Sel-12 (13·19), KS-10×Pant T-3 (1·66) and EC 818703×EC 13042 (0·88) were best specific combiners for ascorbic acid, total soluble solids and yield/plant. Predominance of non-additive gene action plays a greater role in the inheritance of ascorbic acid and total soluble solids in tomato under hill conditions.

Rose production is limited by salinity and highly affected by the nitrogen source present in the nutrient solution. The influence of sodium on several aspects of nutrition has been investigated in ‘Lambada' rose plants using different sources of nitrogen in the fertilization treatment. Experiments using a previously defined mono-shoot model plant and a simplified hydroponic culture allowed us to study the effects of salinity v. nitrogen on NPK uptake during the culture period. Mineral concentrations, nitrate reductase (NR) and glutamine synthetase (GS) activities were also analysed. This study showed that rose plants were more sensitive to saline conditions under NH4+ fertilization without detectable effects on growth or in NPK mineral contents in shoots. Parameters affected most were enzymatic activities analysed such as leaf nitrate reductase activity which was reduced under NH4+ nutrition. Leaf glutamine synthetase was also enhanced by saline conditions. The Na/K ratio showed that under NH4+ nutrition, the highest sodium accumulation occurred in roots. Nitrate uptake did not show a clear pattern related to nitrogen source, however, ammonium uptake was affected by salinity when NH4+ was the sole nitrogen source in the nutrient solution. Potassium and phosphate uptake were always lower when NH4+ was present in the nutrient solution.

Growth and efficiencies of nitrogen and energy utilization for growth by 72 young British Friesian steers (initial live weight (LW) 110 kg) offered a well preserved, formic acid-treated, perennial ryegrass silage with and without supplements of fish meal were examined. Silage was offered either alone or mixed with 50, 100 or 150 g fish meal/kg silage dry matter (DM) and each diet was offered either ad libitum or intakes were restricted to 16, 19 or 22 g dietary DM/kg LW/day. Treatments were imposed over a period of 132 days. Body component weight gains were determined by comparative slaughter.

Increasing the level of either feeding or fish meal increased rates of empty body weight gain linearly (P<0·001) and curvilinearly (P<0·05) respectively. Fish-meal supplementation increased rates of ash and crude protein gain (P<0·001) but, in comparison with the curvilinear response to increasing level of feeding (P<0·001), had small linear effects on fat gain (P>0·01). Consequently, in terms of whole body composition, animals given fish meal were leaner than animals offered silage alone. Fish-meal supplementation had no significant effect on the composition of the carcass but increased the concentration of protein in the liver and gastrointestinal tract.

The increase in nitrogen intake associated with feeding fish meal resulted in a reduction in the efficiency of nitrogen utilization as level of fish meal increased. Nitrogen intake required for maintenance was estimated to be 1·054 g/kg LW0·75. In spite of marked differences in the composition of the empty body-weight gain, there was no evidence to support an effect of fish meal on the efficiency of metabolizable energy (ME) utilization for growth (kf) which was estimated to be 0·346 on the basis of data scaled by LW0·75. ME intake required for maintenance (MEm) was estimated to be 0·536 and 0·502 MJ/kg LW0·75 for silage alone and the 150 g fish-meal level respectively.

Concentrates are the main cash expenditure in smallholder campesino dairying in the highlands of Central Mexico. Improved, low-cost, appropriate feeding strategies have been therefore identified by campesinos as a priority. An on-farm trial was undertaken in 1998 to evaluate the response to supplementation with concentrates by dairy cows in early lactation during the rainy season with restricted access to grazing of ryegrass/white clover pastures. A base of 3·0 kg commercial concentrate/cow/day (S3) was compared against the higher rate used by farmers of 5·0 kg/cow/day (S5). Three farmers with one, and one farmer with two pairs of freshly calved upgraded Holstein cows participated in the trial (24±10·7 days into lactation). Data were analysed by a random block split-plot design where supplementation treatments were main plots and measurement periods were split-plots. Milk yield was recorded once per week for 9 weeks, and live weight and condition score for four 28 day periods. Milk yields were 21·8 for S3 and 21·9 for S5 (±0·714) kg milk/day/cow (P > 0·05); live weight S3 = 444·0 and S5 = 496·0 (±12·663) kg/cow (P > 0·05), and condition score S3 = 1·9, and S5 = 1·8 (±1·127) (P >0·05). There were no significant (P> 0·05) effects of measurement periods, and there was no significant (P > 0·05) interaction. The lack of response in milk yield, live weight or condition score to increased concentrate supplementation demonstrates that at these levels of production and management, the access to grazing of improved pastures, plus limited concentrate, enables cows in campesino systems to meet their nutrient requirements, and the feasibility of efficient milk production from grazed pastures as an appropriate technology. It is also concluded that it is an appropriate technology and that the results have implications for research and extension workers in rural development who have promoted large amounts of concentrate to dairy cows as the only way towards high yields and efficient milk production.

The research was carried out at the animal experimental station of the National Agricultural Research Institute of the French West Indies (Guadeloupe) in 1999. Effects on intake and digestion by sheep of addition of Gliricidia leaves to a diet of 35-day-old Digitaria decumbens (pangola) hay, have been studied. In a first trial (a 4×4 Latin Square design), four rams were fed four diets: hay (G0); hay plus 1300 g of Gliricidia (G0·25), hay plus 2600 g of Gliricidia (G0·50), hay plus 3900 g of Gliricidia (G0·75). Total dry matter intake (DM), hay and Gliricidia intake, total tract and rumen digestibility of DM and its components, microbial and total nitrogen flows were estimated. In a second trial (a 2×2 Latin Square design), the same animals received hay (G0) or Gliricidia (G1·00) ad libitum to estimate the rumen turnover of pangola and Gliricidia fibrous particle. Neutral detergent fibre and crude protein content of the Digitaria decumbens hay and Gliricidia were 746 and 51, 458 and 198 g/kg dry matter respectively. Total dry matter intake (DM) varied from 42·7 to 76 g DM/kg LW0·75 from G0 to G0·75. The rate of substitution of pangola by Gliricidia (decrease of pangola intake for one unit Gliricidia consumed) was 233 g/kg. The digestibility of cell-wall linearly decreased with increasing level of Gliricidia in the diet. No digestive interaction was registered in the mixed diets. The total nitrogen and microbial nitrogen duodenal flows increased with the level of Gliricidia in the diet. The rumen turnover of fibrous particles of Gliricidia was double that of pangola. The incorporation of Gliricidia in diets increases their nutritive value by higher intake and intestinal nitrogen duodenal flows, but no positive digestive interaction was observed between pangola hay and Gliricidia leaves.

This group, which is concerned with the applications of mathematics to agricultural science, was formed in 1970 and has since met at approximately yearly intervals in London for one-day meetings. The thirty-third meeting of the group, chaired by Professor P. K. Maini of the Mathematical Institute, University of Oxford, was held in the Kohn Centre at the Royal Society, 6 Carlton House Terrace, London on Friday, 6 April 2001 when the following papers were read.