Six sites of variable soil type and environments in England and Scotland were sown with winter wheat (Triticum aestivum L. cv. Mercia) in the autumns of 1992 and 1993 with optimum inputs for growth. Crop monitoring between February and grain maturity provided data to investigate environmental and physiological factors important in controlling biomass accumulation.

With increasing use of crop modelling as a tool for interpreting experiments and as crop management decision support systems, it is important that all influences on crop productivity are understood. The ‘radiation use efficiency’ or radiation conversion coefficient provides a convenient basis to study these influences.

Significant differences in seasonal radiation conversion coefficients were observed between sites (P < 0·001), ranging from 2·82 to 3·87 g total dry matter/MJ absorbed photosynthetically active radiation. A series of simple dry matter models were developed to help explain biomass accumulation in relation to a number of environmental variables (using the measured green area index as an input) with correlation coefficients [ges ] 0·98 obtained across all sites. Apart from sunlight, differences in the canopy's ability to accumulate nitrogen and maintenance respiration costs were the most significant factors (P < 0·001). The nitrogen effect suggests changes in the conversion of assimilates with nitrogen availability, despite relatively high nutrition levels ([ges ] 180 kg N/ha).

Over all sites the canopy extinction coefficient could be described as a linear function of the site spring time plant population (P < 0·01). A more detailed model considered canopy light attenuation to vary between sites according to sowing date and autumn/winter plant establishment and environment.

Biological resources used by local people for a long period of time preserve historical records and scientific competence attained while they develop, conserve, maintain and utilize the landrace varieties of those crops sustainably, ensuring their descent to successive generations. Ethiopian farmers and the traditional farming systems they still exercise have a tremendous positive impact on maintaining wheat genetic diversity with the associated indigenous knowledge. Twenty-one durum wheat landraces, 11 of which were collected from North Shewa and the remaining 10 from Bale were examined for five qualitative morphological characters. The long beak character was monomorphic at lower altitude (< 2100 m a.s.l.). The phenotypic frequencies for characters showed that the long and intermediate beak types were found in both sites, with the long one being the predominant type in most of the strategic sites (localities). The short beak type was rare in most of the strategic sites (localities) in Bale whereas in North Shewa its frequency reached a maximum of 51%. Black glume was in rare frequency in most of the strategic sites (localities) and districts (depending on size, a district contains several localities). The three seed colour groups (white, brown and purple) were found in a similar proportion across districts, and in situ conservation zones (farmer-based on-farm crop conservation zones, and depending on size a zone contains several districts) with considerable differences among strategic sites (localities). While white glume colour was predominant at lower altitude (< 2300 m a.s.l.), brown glume was most frequent at higher altitude (> 2301 m a.s.l.). The frequency of the purple seed colour increases with increasing altitude. Intra-population polymorphism was common for most traits. The overall estimate of diversity in in situ crop conservation sites is very high (H′ = 0·81±0·01). The first three canonical functions accounted for 85·5% (48·5, 19·7 and 17·4% respectively) of the variation between varieties. The hierarchical cluster analysis revealed two major clusters and eight subclusters. In most cases, the cluster analysis based on the qualitative traits did not necessarily cluster varieties on the basis of their collection sites. The two major clusters contained varieties from Bale and North Shewa in situ crop conservation zones.

Starch gel electrophoresis was carried out on ten monosomic alien addition lines (MAALs) of Oryza officinalis (CC genome) in O. sativa (AA genome) at Punjab Agricultural University, Ludhiana, India during 1993–1995. The diploid progeny from MAALs were studied for possible gene transfer of isozyme genes. Analysis showed introgression for alleles of wild species for peroxidase, esterase and acid phosphatase isozymes in progeny of MAAL 2, esterase in MAAL 7 and acid phosphatase in MAAL 6, indicating partial homology between the two genomes. MAAL 2 yielded the highest number of recombinants. The potential of addition lines for alien gene transfer as well as for linkage mapping is discussed.

Understanding the role of pollinators in determining the outcrossing rate is very important for the development of synthetic varieties of faba bean. Isozyme markers have been used to study the multilocus outcrossing rate in five cultivars under field conditions and in two locations. The study was carried out at Córdoba (Spain) and at Rennes (France). These two locations were chosen because previously studies showed strong differences in cross-pollination. Multilocus outcrossing rates at both locations, Córdoba and Rennes, were 0·65 and 0·33 respectively. Local differences in pollinator abundance and foraging activity were 26 and 32 times higher, respectively, at Córdoba than at Rennes which could explain an outcrossing rate twice at Córdoba compared with Rennes. So, pollinators may play a prominent role in determining the differences in outcrossing between locations. However, at a local level, there is a highly significant positive correlation between foraging activity and outcrossing only at Rennes (where the number of pollinators is scarce) but not at Córdoba (where pollinators are abundant). We suggest that although pollinators have a major impact on the level of outcrossing, in circumstances where there are a lot of pollinators the differences in outcrossing between cultivars depends on other factors among which is the ability of the genotype itself to outcross. No type of floral display seems to be clearly important in the determination of the outcrossing level in such a case. The implication of our results for faba bean breeding strategies is discussed.

Between 1989 and 1999, 33 experiments tested the effects of potassium (K) fertilizer on the yield and quality of potatoes. The experiments were done on a range of soil types and used varieties and management conditions common to modern commercial production. The average yield in these experiments was 48 t/ha. Nearly half of the experiments were done on soils that had exchangeable K values < 120 mg/l (MAFF Indices 0–1) but use of K fertilizer resulted in statistically significant increases in fresh weight yield in only seven experiments. Generally, soil exchangeable K was a poor predictor of the probability of a yield response. Potassium fertilizer caused an increase in dry weight yield in only four experiments and these experiments were characterized by the absence of irrigation, soils with small amounts of exchangeable K and use of determinate varieties. Re-examination of published data supported the findings in the current work: potatoes are not particularly responsive to K fertilizer and the optimal K application rate is rarely > 170–210 kg K/ha. When applied at the optimal rate, the effects of K fertilizer on tuber dry matter concentration were nonsignificant. Exceeding the optimal K application rate caused occasional reductions in tuber dry matter concentrations particularly if potassium chloride (KCl) was used. In the two experiments where it was tested, application rate and form of K had no effect on crisp fry-colour. The effect of K fertilizer on tuber K concentration was measured in 21 experiments and on average each tonne of fresh weight yield was associated with 4·2 kg K. The range in values was large, 2·8–5·7 and related to soil exchangeable K.

For fertilizer recommendations based solely on the probability of a significant yield response to K fertilizer it is suggested that no more than 210 kg K/ha be applied even on soils with < 120 mg exchangeable K/l. For fertilizer recommendations based on crop K removal, an uptake value of 4·8 kg K/t fresh weight (FW), as has been suggested, would be adequate, although errors in the estimation of yield may lead to over or under application of K. Since there was little evidence to support fertilizer policies that apply more K than is removed by the crop a fertilizer recommendation system based primarily on the probability of a yield response would be more than sufficient.

A field experiment was conducted for 2 years (1993–95) at Central Institute of Medicinal and Aromatic Plants, Field Station, Bangalore, India to evaluate the nitrification inhibitors, benzotriazole, o-nitrophenol, m-nitroaniline and dicyandiamide in a perennial aromatic grass, Java citronella. Citronella responded to applications of high doses of nitrogen (300 kg N/ha/year). The interaction between N doses and nitrification inhibitors was significant. Nitrification inhibitors performed better at the highest N dose (450 kg N/ha/year) and the increase in the essential oil yields was to an extent of 27·3 to 34·6% when compared with ‘N alone’ treatment. The nitrification inhibitors also increased the apparent N recoveries by citronella considerably. The oil content in the herb and its quality were not affected by the treatments. The nitrification inhibitors increased citronella yields and improved N economy.

The aim of the experiment was to determine the importance of liquid digested sewage sludge (‘sewage sludge’) as a source of phosphorus leaching from sandy soils in the UK. The sewage sludge was applied to uncropped loamy sand and sandy loam monolith lysimeters (1·2 m deep) annually for 3 years. The application rate was sufficient to supply approximately 60 kg P/ha annually. An application equivalent to four times this amount was also applied to two other loamy sand lysimeters to test the effects of excessive amounts. Total P (TP), total dissolved P (TDP) and molybdate-reactive P (MRP) concentrations were measured in the drainage water and were compared with leaching from untreated control soils.

After two sewage sludge applications, Olsen's extractable P content of the topsoil had increased: a P surplus of c. 100 kg/ha was required to raise the topsoil concentration by 5 mg/kg. Sewage sludge applications at the lower rate did not increase P concentrations in the drainage. Phosphorus concentrations were generally small and were, as an average of both soil types and nil and lower rate sludge applications, 12, 20 and 34 μg/l for MRP, TDP and TP respectively. Phosphorus leaching losses from the higher rate (excessively large sewage sludge applications) were more variable but not significantly (P > 0·05) different from the other treatments. Average concentrations were 9, 23 and 50 μg/l for MRP, TDP and TP respectively. Leaching from sludge biosolid applications at operational rates to sandy soils moderately well supplied with P is not a major P loss pathway.

Two studies were undertaken to evaluate the effects of cellulase and endoxylanase enzymes on the chemical composition and the fermentation characteristics of grass silage, using the gas production technique. Perennial ryegrass was ensiled in 1 litre glass containers for 90 days with cellulase (0·2 g/kg grass on fresh weight basis) and endoxylanase in the concentrations of 0·05 g/kg grass (Endox 0·05) and 0·2 g/kg grass (Endox 0·2). Subsequently, dried samples, ground through a 1 mm screen, were used in chemical analysis and gas production measurements. In Expt 1, the enzyme treatment significantly decreased silage NDF (P < 0·001), ADF (P < 0·001) and acetic acid (P < 0·01) concentrations and increased lactic acid (P < 0·001) production. In Expt 2, lower concentrations of NDF (P < 0·001) and ADF (P < 0·001) in treated silages resulted in increased sugar concentration (P < 0·001). In this experiment, butyric acid was detected. Addition of cellulase and Endox 0·05 enzymes did not alter silage digestibility. In both studies, cellulase and Endox 0·2 treatments tended to increase the rate of gas production within 10 hours of inoculation with rumen fluid whereas Endox 0·05 had no effect. The volume of gas produced was however greater for the untreated silage than for the enzyme-treated silage samples after 48 h of incubation. The strategy of applying cellulase and endoxylanase to the herbage in the ensiling process proved to be effective in modifying the chemical composition and increasing sugar concentration and the rate of gas production of the silages. Further research on the factors determining enzyme effectiveness is therefore suggested to elucidate the mechanisms leading to higher utilization of the released sugars.

Energy requirements for maintenance and growth were estimated by comparative slaughter in Omani male lambs during the hot summer months (July–October: maximum temperature, 48 °C). Weaned lambs (n = 10 per diet) were fed one of three totally mixed, 160 g CP/kg DM diets that contained 600, 400 or 200 g rhodesgrass hay/kg for low (9·98 MJ/kg, medium (10·3 MJ/kg) and high (11·4 MJ/kg) energy contents, respectively. All diets were balanced to meet the minimum nutritional needs for maximum growth. The trial lasted for 113–114 days. The purpose of having three diets was to induce a broad spectrum of growth rates that could be used in regression analysis (tested for linear, quadratic and exponential effects). Metabolizable energy (ME) intake was regressed on live weight (LW), empty body weight, tissue energy and tissue protein gain and vice versa. Coefficients of determinations were not significantly improved by quadratic or logarithmic regressions over linear relationships. Geometric mean regressions were used to control further biases due to major axis dependence when Y is regressed on X or vice versa. Based on tissue energy gain, the best estimates of ME required for maintenance (MEm) and gain (MEg) were 526 kJ/kg LW0·75/d and 42·1 kJ/kg LW0·75/g LW gain, respectively. Net energy values for maintenance (NEm) and gain (NEg) were 278 kJ/kg LW0·75/d and 20·6 kJ/kg LW0·75/g LW gain, respectively. These equations predicted MEm and NEm requirements that were similar to or slightly greater than those established by the US National Research Council (1985) and the UK Agricultural and Food Research Council (1993) for growing male lambs. The MEg and NEg requirements were substantially greater (by 43–89%) in this respect. Efficiency values were calculated as net energy available for maintenance or gain divided by the metabolizable energy available for maintenance or gain. The efficiency of metabolizable energy used for maintenance and gain was 0·50 and 0·52, respectively, and did not appear to be much different from values for other breeds of sheep in temperate climates. Dietary energy concentrations did not affect the efficiency of energy deposition. The data suggest that Omani sheep in hot climates have greater NEg requirements, and consequently MEg requirements, than other breeds of sheep in temperate climates.

The effects of dietary energy concentration on tissue composition and nitrogen metabolism were determined by comparative slaughter and nitrogen balance trials in Omani male lambs during the hot summer months (July to October; maximum temperature 48 °C). Weaned lambs (n = 10 per diet) were fed on one of three isonitrogenous (160 CP g/kg DM) diets that contained low (9·98 MJ/kg DM), medium (10·3 MJ/kg DM) and high (11·4 MJ/kg DM) metabolizable energy contents. An initial slaughter group of 10 animals was used to estimate the initial body composition. Treatment animals were slaughtered at 113–114 days. Increasing dietary energy concentrations resulted in a progressive increase in empty body, carcass and non-carcass water, protein and fat contents. Increasing dietary energy concentrations also resulted in a greater deposition of energy in carcass fat and a reduced deposition of energy in carcass protein. Dietary energy concentration did not affect the distribution of energy between protein and fat within empty body and non-carcass tissues. Ratios of energy to empty body, carcass or non-carcass weight were not affected by dietary energy concentrations and averaged 17·1, 18·2 and 15·9 MJ/kg respectively. These data indicate that more energy is required to deposit carcass tissues than non-carcass tissues. Nitrogen balance trials (feed N–faecal N–urinary N) conducted midway through the experiment indicated that dietary energy concentration had no effect on nitrogen digestibility or nitrogen retention. However, nitrogen retention determined by comparative slaughter showed that animals fed the low energy diet retained significantly less empty body nitrogen compared to animals fed the high energy diet. Thus, nitrogen retention determined by nitrogen balance trials overestimated direct measurements of nitrogen retention determined by comparative slaughter and this overestimation was greater on the low energy diet.