The effect of water stress, commencing from the late cell division period, on in vivo grain growth was studied in relation to grain sucrose, water status and in vitro starch synthesis. Detached ear experiments were conducted to assess the effect of sink dehydration on grain filling processes under non-limiting source conditions. Water stress caused premature grain desiccation and resulted in a marked decline in grain sucrose and reduced grain weight. Both sucrose uptake and conversion to starch in vitro were increased by mild water stress (solute potential (Ψs)−0·8 MPa). However, a decline in Ψs below this optimum resulted in reduced sucrose uptake and starch synthesis not attributable to a reduced supply of sucrose. Stressed grains which failed to accumulate dry matter in vivo showed significant starch synthesis when cultured in vitro. Grains from in situ and osmotically stressed plants showed a lower capacity for starch synthesis in vitro. The results indicate that grain filling processes under stress conditions are limited by (1) low substrate availability and low Ψs within the sink i.e. an unfavourable seed environment (non-lasting effect) and (2) reduced synthetic capacity of the sink (carry-over effect).

Intensive dairy farming with low N use efficiencies may have adverse environmental impact through nitrate leaching. The residual effects of six different temporary grasslands (1994–96) on yield and nitrate leaching in the following cereal crops (1997–99) were investigated on a loamy sand in central Jutland. The grasslands were unfertilized grass–clover and fertilized ryegrass subject to cutting or continuous grazing by dairy cows with two levels of N in feed supplements. In the first year there was sufficient residual effect of the grazed grasslands to obviate the need for supplementary fertilizer, but in the following years gradually more fertilizer N was required to obtain optimal yields. Nitrate leaching decreased as a function of time after cultivation of grassland, but grassland management had little effect on the subsequent nitrate leaching (6 to 36 kg N/ha in unfertilized plots). Application of cattle slurry to cereals influenced nitrate leaching more than the history of the grassland and caused the annual mean nitrate concentration to exceed the EU Drinking Water Directive upper limit in most cases. Presumably, large differences in N-input during the grassland phase of the crop rotation had relatively little effect on the subsequent N release because of variable N losses during grazing. Possibilities for further improvement of the utilization of grassland N following cultivation are limited when the current knowledge has been implemented. If the N use efficiency of dairy farming systems is to be further improved the utilization of N during the pasture phase is crucial.

Phosphorus (P) availability is often restricted in alkaline soils. The objective of this study was to determine if the plant availability of P from liquid ammonium polyphosphate fertilizer (APP) would be enhanced when blended with fluid sulphur (S) sources of differing acidification potential. Eight field studies with ‘ Butte 86 ' hard red spring wheat (Triticum aestivum L.) were conducted in 1995 and 1996 in eastern North Dakota, USA, comparing no P, 9·8 kg/ha of P, and 9·8 kg P/ha plus 11·2 kg S/ha from different S sources. The S sources were elemental sulphur (ES), ammonium sulphate (AS), ammonium bisulphite (ABS), ammonium thiosulphate (ATS), potassium thiosulphate (KTS) and potassium sulphate (KS). The P and S fertilizers were banded with the seed at planting. Phosphorus fertilization gave a typical ‘starter effect’, stimulating tillering, early growth and P uptake. Phosphorus uptake at the 4–5 leaf stage was increased by addition of acid-forming S fertilizers to the APP. Grain yield response to P applied with the seed was typically 400 kg/ha. The enhanced P uptake observed at the 4–5 leaf stage when certain S sources were added to APP did not lead to additional grain yield. Wheat grain yield in North Dakota comes almost entirely from the contributions of the main stem, T1 and T2 tillers, and initiation of these tillers was essentially complete when APP alone was banded with the seed.

The response of eight long-duration pigeonpea [Cajanus cajan (L) Millsp.] genotypes to irrigation was studied at Gwalior in Central India during the 1990–91, 1991–92 and 1992–93 growing seasons on an Inceptisol. The crop was grown at two spacings as it was expected that crop density could interact with the crop's ability to extract soil moisture. The irrigation treatment received furrow irrigation four times during the 1990–91 and 1992–93 seasons and twice during the 1991–92 season. Grain yields of all genotypes were 11 % higher when planted at higher density than at low density. There was a differential variation in yield and harvest index among genotypes due to season but not due to spacing and irrigation suggesting the validity of the present approach of testing genotypes under optimum conditions. Grain yield declined by 21 % from the 1990 to 1992 season. The decline was > 1 t/ha in some cultivars (ICPL 366, GW3), and between 0·5 and 1·0 t/ha in others (NP [WR] 15, ICP 87143 and ICPL 84072). In others (Bahar, ICP 9174, ICP 8860) the yield fluctuation was < 0·5 t/ha. The genotypes' mean yields were as high as 2·7 t/ha for ICPL 87143, ICPL 84072 and ICPL 366. There was a significant reduction in both grain yield (16 %), and also above-ground plant dry mass (18 %) due to soil moisture limitation in the unirrigated treatment. Both the above-ground plant dry mass and grain yields were significantly more at high plant density than at lower plant density especially with irrigation. The genotypes were found to differ in their response to production environment (irrigation, spacing and to the undefined differences of the 3 years). Genotypic variation in yield within a production environment was found to vary in relation to changes in harvest index and across environment (irrigation, seasons) due to variation in total dry matter production. A lack of negative relationship between the total dry matter and harvest index suggests the possibility of optimizing both for obtaining higher yield from long-duration genotypes.

The objective of this study was to assess the efficiency of a pedigree intra-cultivar selection, based on widely spaced individual plant performance, in a traditional snap bean (Phaseolus vulgaris L.) cultivar, aiming to restore or even improve the cultivar. The programme started with the target of earliness and yield stability, and was progressively advanced with the target of seed shape uniformity. Two parallel pathways were followed: under greenhouse conditions (four generations of selection) and under field conditions (two generations of selection). The average response to selection was 2·43–3·15 and 0·13–0·42 pods/plant per generation for earliness and yield, respectively. The coefficient of variability (CV) of earliness decreased from 81·33 to 39·43 % and from 61·31 to 42·51 % for greenhouse and field grown progenies, respectively. For yield, the CV showed a low decreasing rate, and was stabilized at the end-value of almost 28 %. The results were confirmed during two direct evaluation tests. Firstly, the evaluation of 21 families, as individual spaced plants, showed mean values for earliness of 18·99–22·94 pods/plant and for yield of 32·89–33·09 pods/plant. Secondly, the evaluation of improved selections from the greenhouse and the field and of the source cultivar, in a dense stand, showed that all the selections produced high and stable early fresh pod harvest even 53 days after planting, while the control was still at the vegetative phase. The yield of selected progenies was 219–242 % superior compared with source material. Also, seed stocks of all selections were of the normal long shape. Short-seed progenies were excluded from the breeding programme, since they lacked earliness and stability of performance. The results demonstrate conclusively that it is possible to simultaneously improve earliness and pod yield through diminishing plant-to-plant variability.

Morphophysiological characters, designated as descriptors by the International Union for the Protection of New Varieties of Plants (UPOV) and the International Plant Genetic Resources Institute (IPGRI), and allozyme variation were used to study genetic diversity among four cabbage (Brassica oleracea L. var. capitata L.) open pollinated (OP) populations. The morphological and physiological characters, and gene frequencies among OP populations were analysed by using cluster (CA) and principal component analysis (PCA). Both methods gave the same clustering of OP populations. The relationships found among OP populations by analysing UPOV descriptors (30 characters) and IPGRI descriptors (30+14 characters) were similar. The relationships among OP populations obtained from gene frequencies were not similar to those obtained from morphophysiological characters, but two of the four OP populations were clustered together by both categories of data. The biggest correlation between the relationships among OP populations obtained from morphophysiological characters and those obtained from gene frequencies was r = −0·44 and r =−0·38 given by PCA and CA respectively. The importance of each character or allele with respect to the relationships among OP populations were also detected by PCA.

Forty-eight high genetic merit Holstein/Friesian dairy cows with Predicted Transmitting Abilities for milk fat plus protein yield, calculated using 1995 as the base year (PTA95 fat plus protein), of 40·0 kg, were used in an eight treatment, two period (period length = 8 weeks) change-over design experiment. Diets were offered ad libitum in the form of a complete diet. Treatments comprised a high and medium feed value silage, with concentrates being incorporated into the diet at proportional inclusion rates of 0·10, 0·30, 0·50 and 0·70 of total dry matter with the high feed value silage, and at 0·32, 0·48, 0·64 and 0·80 of total dry matter with the medium feed value silage. The high feed value silage was produced from a primary regrowth herbage (regrowth interval of 33 days) which was wilted prior to ensiling, while the medium feed value silage was produced from a primary growth herbage harvested on 9 June 1995. The high and medium feed value silages had estimated metabolizable energy concentrations of 12·4 and 11·3 MJ/kg DM respectively. Animals commenced treatments after a mean post calving interval of 26 days.

Irrespective of silage feed value, total dry matter intake and milk yield tended to increase with increasing proportion of concentrate in the diet. Milk protein concentrations increased to concentrate inputs of 0·50 and 0·64 of total DM with the high and medium feed value silages respectively, but decreased at the highest concentrate inclusion rates. Milk fat concentrations tended to decrease at higher concentrate inclusion rates. The milk yield responses to increasing proportion of concentrate in the diet have been described by a pair of significantly different equations: Y = 34·2−11·9×0·0101x and Y = 34·2−28·5×0·0101x for the high and medium feed value silages respectively (where Y = milk yield (kg/day) and x = concentrate proportion in the diet on a dry matter basis). Similarly, milk fat and milk protein yields for the two silage types have been described by pairs of significantly different equations. Using these milk yield response equations, it can be calculated that at a concentrate proportion in the diet of 0·32 total dry matter, an additional 3·7 kg of milk per day would be produced by offering the high, rather than the medium feed value silage, while at a concentrate proportion of 0·70 total dry matter, the milk yield benefit associated with the high feed value silage was reduced to 0·6 kg per day. Similarly, total dry matter intakes for animals offered the high feed value silage were 7·4 and 0·8 kg per day greater than for animals offered the medium feed value silage, at concentrate proportions in the diet of 0·32 and 0·70 total dry matter, respectively. These responses indicate that at low concentrate inclusion rates in the diet, silage feed value has a major influence on animal performance, while at higher concentrate inclusion rates, the importance of silage feed value is reduced.

There is the potential for arsenic to enter the human food chain via ingestion by grazing animals. Data on the transfer of arsenic to ruminants have been too sparse to allow the development of dynamic models to predict changes in the arsenic contents of different tissues following ingestion. A study is described during which a group of 6-month-old lambs were given a single oral administration of 73AsCl3. Subsequently, concentrations of 73As in the tissues of groups of lambs slaughtered at intervals over a period of 181 days were determined. A true absorption coefficient of 0·46±0·055 (mean±S.E.) was determined which is considerably lower than expected from previous studies of non-ruminant animals which demonstrate complete absorption for inorganic arsenic. The resultant data were used to develop a compartment model to describe arsenic behaviour in sheep tissues. The derived model accounted for 80 % (n = 100) of the observed variation in the data. The model predicts that arsenic concentrations in tissues rapidly (< 40 days) reach equilibrium with the dietary intake level. Equilibrium transfer coefficient values (the ratio of the arsenic concentration in a tissue to the daily dietary intake of arsenic) for the important food-chain tissues were calculated as: (2·5±0·67)×10−3 days/kg for muscle, (9·1±1·96)×10−3 days/kg for liver and (1·1±0·14)×10−2 days/kg for kidney.

Rumen biohydrogenation of dietary polyunsaturated fatty acids (PUFA) is a significant limitation on any attempt to manipulate the PUFA content of ruminant products (meat or milk). This study examined rumen biohydrogenation of PUFA, the effects of PUFA on other aspects of rumen metabolism and fatty acid flow to and digestion in the small intestine of steers fed on different sources of lipid. Animals were fed ad libitum on grass silage and one of four concentrates (60:40 forage:concentrate on a dry matter basis) containing differing sources of lipid: megalac (rich in C16:0; M), linseed (rich in C18:3n-3; L), fish oil (rich in C20:5n-3 and C22:6n-3; FO) and a mixture of linseed/fish oil (LFO). Diets were formulated so that total dietary oil intake was approximately 60 g/kg of the DM intake, approximately half of which was from the experimental test oil. Rumen NH3-N (P = 0·09) and total VFA concentrations (P = 0·007) were higher on L, FO and LFO compared to M. Dry matter intakes did not differ across treatments and averaged 7·2 kg/day. Intake and flow of fatty acids to the duodenum was 323, 438, 344 and 381 (S.E.M. 9·1; P < 0·001) and 432, 489, 412 and 465 (S.E.M. 18·5; P < 0·1) g/day for M, L, FO and LFO, respectively. Biohydrogenation of C18:1n-9 was lower than all the other unsaturated fatty acids and it was lower of FO and LFO compared to M and L, on average 66·1 and 72·2 %, respectively. Biohydrogenation of C18:2n-6 averaged 89·8 % across treatments and was lower (P < 0·05) on M compared to L and FO. Biohydrogenation of C18:3n-3 averaged 92·1 % across treatments and was lowest on M (88·8 %) and highest on L and LFO (94·3 %). Biohydrogenation of C20:5n-3 and C22:6n-3 averaged approximately 91 and 89 % across the treatments, respectively. Small intestinal digestibilities of all fatty acids were high. In conclusion, feeding different sources of lipid with different fatty acid composition had significant effects on rumen function. The PUFA in whole linseed were only partially protected from biohydrogenation by the seed coat and in contrast to previous reports the C20 PUFA in fish oil were biohydrogenated to a large extent.