The most important harvested organs of crop plants, such as seeds, tubers and fruits, are often described as assimilate sinks. They play little or no part in the fixation of carbon through the production of sugars through photosynthesis, or in the uptake of nitrogen and sulphur, but import these assimilated resources to support metabolism and to store them in the form of starch, oils and proteins. Wild plants store resources in seeds and tubers to later support an emergent young plant. Cultivated crops are effectively storing resources to provide us with food and many have been bred to accumulate much more than would be required otherwise. For example, approximately 80% of a cultivated potato plant's dry weight is contained in its tubers, ten times the proportion in the tubers of its wild relatives (Inoue & Tanaka 1978). Cultivation and breeding has brought about a shift in the partitioning of carbon and nitrogen assimilate between the organs of the plant.

The effect of a range of one-year set-aside treatments on soil mineral nitrogen (SMN), during the set-aside period and in a following wheat crop were studied in a phased experiment at five sites from 1987 to 1991. Ground cover options permitted under the UK government's ‘set-aside’ scheme, including natural regeneration, autumn sown Italian ryegrass (Lolium multiflorum), spring-sown legumes and cultivated fallow, were compared with a control treatment of continuous cereals managed with fertilizer inputs. In the first of three phases in this experiment, an uncultivated fallow (kept weed-free) and autumn-sown forage rape (Brassica napus) were included as extra treatments. There were large differences in total SMN (0·0–0·9 m) between sites, ranging from 16 to 205 kg N/ha, reflecting differences in soil type, which ranged from clays to sands, and previous cropping husbandry. Differences in SMN between set-aside treatments during the first winter of the set-aside year were small, but increased during the following summer. Amounts of SMN were greatest after cultivated fallow (46–178 kg N/ha) and least after ryegrass (26–111 kg N/ha). Natural regeneration and spring sown legumes were more variable in their effect on SMN. Compared to continuous cereals, there was a build up in SMN during bare fallow, but a reduction under ryegrass, prior to returning to wheat cropping in the autumn after set-aside. SMN results suggest there was an increased nitrate leaching risk for bare fallow and natural regeneration set-aside, compared to sown ryegrass covers, in the winter following ploughing out of set-aside. This risk could be minimized by earlier sowing of winter cereals following set-aside or sowing with winter oilseed rape rather than cereals to maximize crop nitrogen (N) uptake, during the autumn growth period.

Averaged across five sites, residual SMN supply in the spring of first test year cereal crops for all set-aside treatments was similar to that for continuous cereals, suggesting over-winter losses by N leaching or immobilization. The low residual N fertility after rotational set-aside suggested that following crop N recommendations should be the same as for continuous cereals. Amounts of SMN were less each year in spring than in the preceding autumn in both the set-aside and first test cereal crops. The results suggested that a ryegrass cover appeared to be the most environmentally favourable option for rotational set-aside management, as it minimized the amount of readily leachable N both during and immediately after the set-aside period.

The effects of spring top-dressed applications of broiler litter, pig slurry and cattle slurry on winter wheat and winter barley yield and quality were investigated on a field scale at three UK sites between 1992 and 1994, using commercially available application equipment. Broiler litter was applied at rates ranging from 5·3 to 8·8 t/ha, and slurries from 54 to 89 m3/ha. Few practical problems were encountered when spreading broiler litter, but when spreading cattle slurry there was some crop damage and soil compaction from the tanker wheelings adjacent to tramlines. Coefficients of variation for manure spreading using commercial spreaders ranged from 20 to 32%. Spring applied manures increased yields of winter wheat and winter barley, and lowered optimum inorganic fertilizer nitrogen (N) rates. When the N efficiency of the manures was compared to that of inorganic fertilizer N, broiler litter N efficiencies ranged from 10 to 49%, cattle slurry was c. 30% and pig slurry c. 50%. The experiments demonstrated that poultry litters and slurries can be applied successfully to growing cereal crops in spring as part of an integrated policy for N supply.

15N-labelled fertilizer urea was applied at increasing rates (0–200 kg N/ha), in spring, to winter wheat crops in the Canterbury region of New Zealand in three successive seasons (1993/94, 1994/95 and 1995/96). Recovery of fertilizer N by the crop (grain, chaff, straw and roots) ranged from 43–58% (mean 48%). The quantity of fertilizer N retained in the soil (0–40 cm), at harvest, ranged from 26–42%. Of the labelled N present in the soil, over 95% was present in organic form and 60–80% was retained in the surface 0–10 cm layer. Since soil organic matter represents a substantial sink for fertilizer N there is a need to characterize the nature of this organic pool of N more fully. The quantity of inorganic N present in the soil profile at harvest ranged from 20–46 kg N/ha and labelled fertilizer-derived N contributed less than 16% (mean 9·2%) to this inorganic pool. Loss of fertilizer N from the crop/soil system (i.e., labelled N not recovered in the crop or soil at harvest) varied from 12–26% (mean 18%). Losses were attributed mainly to denitrification since conditions were not conducive for ammonia volatilization or leaching of nitrate. In agreement with European research, it was concluded that almost all of the N at risk of leaching over the winter originates from mineralization of soil organic N and not from unused fertilizer-N applied in spring.

The effect of drought stress in isolation, or in combination with beet yellows virus infection, on sugar beet growth was studied in the field and glasshouse. Drought reduced total plant weight by 26%, due to 20 and 29% reductions in foliage and storage root yields respectively. Sugar extraction efficiency was depressed by an increase in amino-nitrogen impurities. Drought did not limit water extraction depth, despite decreasing lateral root growth in proportion to total weight. During the field experiments, total crop cover was decreased in all the droughted treatments (halved in some cases) for at least part of the season. Consequently, these treatments intercepted 12% less light, which in combination with a 16% decrease in the dry matter/light conversion coefficient, led to the decrease in growth. The decrease in conversion coefficient was due to temporary closure of the stomata rather than a function of drought-induced damage to the photosynthetic mechanism. The absolute effect of drought remained the same irrespective of whether the plants were infected with beet yellows virus, i.e. there was no interaction between the two stresses. The reasons for this lack of interaction are discussed but it is likely that the stress effects were mediated at different times of the day and season.

Two pot experiments were performed to study the effects of three pre-emergence herbicides (terbutryn/terbuthylazine, trietazine/simazine and prometryn) and a post-emergence herbicide (bentazone) on nodulation, symbiotic nitrogen fixation, growth and yield of pea (Pisum sativum L.) grown in perlite under nitrogen-free conditions. All pre-emergence herbicides decreased nodulation, total nitrogenase activity, net photosynthesis, leaf area, root and shoot dry weight, nitrogen content and seed yield of peas. The effects of herbicides increased with increase in rate of application. Of the herbicides tested, terbutryn/terbuthylazine and trietazine/simazine had the greatest adverse effects. Pea plant biomass (root plus shoot) was correlated with plant nitrogen content but not total nitrogenase activity. The results of the experiments suggested that the decreased growth of herbicide-treated plants was due to direct effects of the herbicides on peas and not due to indirect effects of the herbicides on rhizobia.

Field trials were undertaken in Suffolk in commercial crops of autumn-sown oilseed rape cv. Capricorn during 1993/94, cv. Apex in 1994/95. Plots were artificially infected with beet western yellows virus (BWYV) using viruliferous Myzus persicae, giving 73 to 94% infection. Control plots had natural infection ranging from 0 to 17·8%. Destructive plant samples were taken from each of the infected and control plots throughout the seasons for growth analyses, and final yields were measured on 44 m2 areas combine harvested from each plot. The seed yields of infected plots were 26 and 11% lower than control plots in 1994 and 1995 respectively (P<0·001).

Harvested seed yields were shown to be inversely proportional to the area of the plot that was inoculated with BWYV. Infection significantly lowered the oil content in 1995 from 47·9 to 46·8% (P<0·001), and increased glucosinolate levels from 16·12 to 18·37 μmol/g (P<0·01). BWYV caused a significant reduction in plant height and in numbers of primary branches in the 1993/94 trial and had an effect on the dry weight of the leaves, stalks, racemes and pods at some sample dates in both seasons. Virus-testing of infected plants showed that BWYV was present in the pod wall, the septum and seed coat; two of 78 embryo samples also contained virus. It was concluded that BWYV can cause significant yield losses in those years in which there is a high incidence of virus in the overwintered crops.

The long-term effect of fertilizers and an integrated nutrient supply system was studied in a rice–rice sequence for 8 years at Hyderabad in India from 1988/89 to 1995/96. Nutrient uptake and seed yield improved with increase in fertilizers up to the recommended dose of 120, 60, 40 kg/ha, N, P2O5 and K2O in the rainy and post-rainy seasons during the 8 years sequence cycles. The soil became enriched in organic carbon (OC) and maintained the available P while K concentration was reduced from medium to low status after 8 years. Integrated nutrient supply by incorporating glyricidia or FYM 15 days before transplanting the rice thereby substituting 25% nitrogen in the rainy season and application of only 75% of the recommended fertilizers in the post-rainy season maintained the overall mean yield at a level equal to that from the continuous application of the recommended fertilizer dose. The practice saved 30 kg N, 15 kg P2O5 and 10 kg K2O/ha in every season and improved the OC% and available P of the soil. The overall mean production of rice grain following the substitution of 50% nitrogen with glyricidia in the rainy season and fertilizer application at the recommended dose in the post-rainy season was also equal to that given by the application of the recommended fertilizer dose applied in every season and increased the OC% and available P of the soil. This procedure reduced the fertilizer dose in the rainy season by 60 kg N, 30 kg P2O5 and 20 kg K2O/ha.

Root re-growth, following aluminium (Al) stress, has been used as an indicator of Al stress tolerance. Genetic variation in root re-growth characteristics among eight triticale genotypes was investigated by a diallel analysis. Highly significant variation due to both general combining ability (GCA) effects and specific combining ability (SCA) effects indicated that both additive effects and non-additive effects were important in explaining the genetic variation for Al tolerance. The high estimates of heritability and the predictability ratio for root re-growth revealed the preponderance of additive genetic variance in the inheritance of Al tolerance. Differences in patterns of GCA effects and SCA effects among the parents provided strong evidence that the genetic control of variation for Al tolerance as assessed by root re-growth was a complex polygenic system. Three Al-tolerant genotypes, Tahara, Abacus, and 19th ITSN 70–4, were found to be the best general combiners for larger root re-growth, and they could be used in hybridization programmes to improve Al stress tolerance by following a simple pedigree method of selective breeding.

Pod and seed growth were studied in two experiments in which the plant's source-sink relationships were modified by (a) manually pruning an autumn-sown, indeterminate white lupin variety, Lunoble, to a determinate form, and (b) by growing a determinate variety, Lucyane, at densities ranging from 7 to 35 plants/m2. The pruning experiments indicated that the faster pod growth rate of determinate genotypes was not an inherent genetic trait but an indirect physiological consequence of the plant's changed architecture. In the density experiment, crop dry matter (DM) and nitrogen (N) were maximum at the end of pod extension in late July and similar across the plant density range at c. 12 t DM and 320 kg N/ha. Therefore, the amount of dry matter per plant decreased proportionately with the increase in plant number. The DM and N contents of the pod walls were also maximum at the end of pod extension, but seeds contained only a third of their final DM and a quarter of their final N. Protein accumulation during the final stages of seed growth, therefore, depended on the remobilization of nitrogen from other plant organs, primarily the leaves and pod walls. Nitrogen withdrawn from the leaves accounted for 44% of the gain in the pods, and N withdrawn from pod walls for 50–60% of the gain in the seed.

Seed number/m2 was the major yield component. Seeds and pods mainly aborted during early development, but seed number per pod was also decreased by some seed abortion after full pod extension, especially in first-order pods of plants grown at high density. The number of late-aborted seeds was negatively correlated with the amount of N remobilized from the pod wall. In determinate lupins, which have highly synchronous flowering and pod development, the large and sudden remobilization of nitrogen from leaves and pod walls for seed growth and protein accumulation triggered crop senescence.

In four field experiments, the effects of single nitrogen (N) applications at planting on yield and nitrogen uptake of potato (Solanum tuberosum L.) was compared with two or three split applications. The total amount of N applied was an experimental factor in three of the experiments. In two experiments, sequential observations were made during the growing season. Generally, splitting applications (up to 58 days after emergence) did not affect dry matter (DM) yield at maturity and tended to result in slightly lower DM concentration of tubers, whereas it slightly improved the utilization of nitrogen. Maximum haulm dry weight and N content were lower when less nitrogen was applied during the first 50 days after emergence (DAE). The crops absorbed little extra nitrogen after 60 DAE (except when three applications were given). Soil mineral N (0–60 cm) during the first month reflected the pattern of N application with values up to 27 g/m2 N. After 60 DAE, soil mineral N was always around 2–5 g/m2. The efficiency of N utilization, i.e. the ratio of the N content of the crop to total N available (initial soil mineral N+deposition+net mineralization) was 0·45 for unfertilized controls. The utilization of fertilizer N (i.e. the apparent N recovery) was generally somewhat improved by split applications, but declined with the total amount of N applied (range 0·48–0·72). N utilization and its complement, possible N loss, were similar for both experiments with sequential observations. Separate analysis of the movement of Br− indicated that some nitrate can be washed below 60 cm soil depth due to dispersion during rainfall. The current study showed that the time when N application can be adjusted to meet estimated requirements extends to (at least) 60 days after emergence. That period of time can be exploited to match the N application to the actual crop requirement as it changes during that period.

This study was carried out at the University of Ankara, Faculty of Agriculture, Field Crops Department experimental field during 1994–1996. Two flax (Linum usitatissimum L.) cultivars having two different flower colours were used as the study material. The cultivar with white flowers was used as a receptor and the violet coloured cultivar was used as a donor.

Average cross-pollination ratio was 1·81% in 1994 whereas it was 0·93% in 1995. The highest cross-pollination was obtained from third experimental design as 4·85% in 1994 and 3·21% in 1995. There were differences among the experimental designs in respect to cross-pollination. The results of this research showed that cross-pollination ratio decreased when distance between donor plants increased.

Transplant crops derived from in vitro produced plantlets of cultivars differing in earliness were grown in three experiments in three years in the Netherlands, during field periods of maximally 12 weeks. Seed tuber crops were included in the first year. Fresh tuber yield was analysed as the result of the radiation intercepted by the crop's canopy (AIR; accumulated intercepted radiation), the efficiency of conversion of intercepted radiation into dry matter (RCC; radiation conversion coefficient), the proportion of dry matter allocated to tubers (HI; harvest index), and the tuber dry-matter concentration (TDMC). Transplant crops had a lower AIR and lower yields than crops from seed tubers. Variables RCC, HI and TDMC were not affected by the type of propagule used. In transplant crops, yields from early cultivars could be extremely low when compared to later cultivars, due to a low AIR. This cultivar effect did not occur in crops from seed tubers. Among transplant crops, the lower AIR was the most consistent reason for lower tuber yields of earlier cultivars. It resulted from a slower increase in soil cover after transplanting and a lower maximum soil cover, both caused by a relatively high allocation of dry matter to tubers immediately after transplanting and resulting first in reduced haulm growth rates and subsequently also in reduced total growth rates. Senescence was not different. A higher HI partly compensated the lower AIR of the earliest cultivars. RCC and TDMC were not consistently affected by cultivar's earliness in the transplant crops.

Three landraces of bambara groundnut (Vigna subterranea (L.) Verdc.) were grown as crop stands in controlled environment glasshouses at the Tropical Crops Research Unit, University of Nottingham, in 1995. Two soil moisture treatments were imposed: irrigated to 90% field capacity each week and irrigated to 60% field capacity until establishment (27 days after sowing) with no further irrigation. Seasonal mean fractional interception varied between 0·20–0·37 for the droughted treatments and 0·62–0·74 for the irrigated treatments, resulting in cumulative intercepted radiation of 228–350 MJ/m2 and 662–794 MJ/m2, respectively. The maximum total dry matter (DM) produced was 5·8 t/ha at final harvest (145 days after sowing) with a pod yield of 2·7 t/ha. Under moisture stress there was little difference in DM production between landraces, with the highest total DM of 1·1 t/ha and a pod yield of 0·05 t/ha, representing a harvest index of 0·05 compared with an average of 0·46 for the irrigated treatments. The conversion coefficient was reduced from 1·00 under irrigation to 0·51 g DM/MJ radiation intercepted by soil moisture stress. Two of the landraces showed adaptive mechanisms to avoid drought; these are discussed in relation to maximizing seasonal radiation interception.

Herbage digestibility, which to a large extent governs the animal's intake, is not easily predicted for grazing animals, and can vary due to different grazing managements. The objective of this study was to build a model for a range of defoliation managements, which takes account of vegetative grass tiller structure, rather than dates of cutting or grazing, as done usually. An experiment was conducted in 1997, near Toulouse, to examine the digestibility of cocksfoot whole lamina and lamina segments (15 cm) for three defoliation regimes. These regimes mimicked severe and lenient intermittent defoliations plus a frequent defoliation treatment over a six-week period. Data were collected for (i) lamina mass and digestibility for the youngest expanded lamina, (ii) lamina appearance rate, lamina and sheath lengths.

Laminae digestibility, measured over time, varied greatly with the defoliation regime both for the youngest full expanded lamina and all laminae on a tiller. Digestibility of the youngest fully expanded lamina decreased from one leaf insertion level to the next, but this decrease was lowest when the defoliation regime was frequent. There was also a consistent decrease in the digestibility of a lamina from its tip to its base. Sheath and lamina lengths varied with treatment in a different way to lamina digestibility. During frequent defoliation, sheath and lamina lengths both increased slightly while they showed substantial increases in the two other treatments. Lamina length increased from one insertion level to the next, and resulted in the addition of less digestible lamina segments rather than reducing overall lamina digestibility. Sheath length, through its influence on leaf appearance rate and lamina length, could be used to predict the digestibility of laminae over time according to leaf insertion level and the difference in the digestibility observed from the tip to the base of a particular lamina. Sheath length could therefore provide a basis for predicting the time course of grass digestibility for different combinations of defoliation frequency and height.

A glasshouse experiment in 1997 at Wye College, University of London, investigated the uptake of 35S-SO4 at two growth stages. When labelled S was applied at growth stage 24 on 20 January only 14% of available sulphur was detected in the plant parts. There was a progressive increase in uptake into the newly emerged leaves. The leaves, which emerged after the application of the radiolabelled sulphur solution was complete, imported sulphur from other parts of the plant. At final harvest the ears had become a major new sink and had imported 68% of the labelled sulphur.

When labelled sulphur was applied on 7 March at growth stage 41–45, an average of 93% of available sulphur was taken up during the 3 days exposure period. The major portion was quickly translocated and recovered from the aerial parts. At final harvest 53% appeared in the grain. The experimental results demonstrated that sulphur reserves can be remobilized to developing sinks. It is suggested that sulphate ions can be retained as a reserve pool by the plant until they are required by actively developing sinks.

The composite effects of two irrigation frequencies (one irrigation at crown root initiation stage and five irrigations at five critical physiological stages of wheat), eight nutrient treatments consisting of N, P and K either applied alone or in combinations at the recommended doses (N:P2O5:K2O at 120:60:40 kg/ha) on population and dry weight of weeds and on the growth, nutrient uptake and yield of wheat were investigated. Observations on the components of the weed population and their biomass made at 60 DAS did not reveal any significant difference between the high and low frequency irrigation. Among the nutrient treatments, the N-treated plots (N, NP, NK and NPK) had a higher population and biomass of grass weeds, whereas sole P and K application or their combination produced the greater growth of broad-leaved weeds. However, the overall weed competition was significantly higher in the P- and K-treated plots than in the N-treated plots. The NP, NPK, NK and N treatments produced significantly higher values for dry weight, crop growth rate, leaf area, number of tillers, nutrient uptake, number of ear-bearing tillers, protein content and grain yield than the other treatments. Weeds in unweeded control plots did not significantly affect wheat growth (CGR, dry weight, tillers/plant) and uptake of the nutrients except of the P at 60 DAS. However, the number of ear-bearing tillers, grains per ear and yield were significantly higher in the weed-free plots than in the unweeded control treatment.

A semi-controlled environment study was conducted from May to September 1996 in Wageningen, The Netherlands, to investigate the interaction between growth and development in bambara groundnut (Vigna subterranea) and the influence of photoperiod on dry matter partitioning. The experimental design was a split-plot with four photoperiods (10·5, 11·8, 13·2 and 14·5 h/d) and two light treatments: unshaded and shaded (42% light reduction). The selection used was ‘DipC94’ from Botswana. The dates of 50% flowering and 50% podding were determined, and samples of plants were harvested at 22, 36, 50, 64, 78, 92, 106 and 120 days after sowing. Total dry matter production was 41% lower in the shaded treatment than in the unshaded treatment, but the rates of progress from sowing to flowering and flowering to podding decreased by only 3 and 12% respectively. This suggests that growth and development in bambara groundnut are largely independent. Photoperiod influenced dry matter partitioning indirectly, through its influence on the onset of podding. There were, however, no strong direct photoperiod effects on dry matter partitioning, either before or after the onset of podding.

Winter wheat (Triticum aestivum L., cv Mercia) was grown at Rothamsted over three seasons (1992/94/95) with plant-available soil P (Olsen-P) ranging from very deficient to superoptimal (1–52 mg P/kg; ADAS soil P Index 0–4). Critical Olsen-P for 95% maximum grain yield changed little between years and averaged 9 mg P/kg. Total-P and inorganic-P (Pi) were measured in whole shoots several times between late tillering and anthesis to see if Pi was a better indicator than total-P of the adequacy of P supply for maximum grain yield. Inorganic-P accumulated in shoot tissue water with increasing Olsen-P to a maximum concentration of c. 15 mM. Inorganic-P was a better indicator of crop P status as there was less variation in critical values between seasons and with crop growth stage. Expressing Pi concentrations on a tissue water basis (Piw) reduced the effect of differences in soil water supply and also offers the prospect of in situ testing. Over the three seasons, critical shoot Piw for 95% maximum grain yield averaged 4.7 mM (range 4·3–5·8 mM) during stem elongation.

We constructed a genetic linkage map of grasspea (Lathyrus sativus L.; 2n = 14) from 100 F2 individuals derived from a cross between PI 426891.1.3 and PI 283564c.3.2. A total of 71 RAPD, three isozyme and one morphological markers segregated in the F2 progeny. A small fraction of markers (12%) deviated significantly from the expected Mendelian ratio (1[ratio ]2[ratio ]1 or 3[ratio ]1). Out of 75 markers, 69 (one morphological, three isozyme and 65 RAPD markers) were assigned to 14 linkage groups comprising 898 cM. The average distance between two adjacent markers was 17·2 cM. The present linkage map will serve as a reference point for further linkage studies in grasspea.