Three experiments on winter wheat, each lasting 5 years and on different soil types, were used to test the effects of incorporating different amounts of straw, mainly to determine the importance of achieving uniform distribution to avoid adverse effects on grain yield. Decreases in crop growth and/or grain yield as a consequence of incorporating straw were detected in the first year. The decreases were much larger in one experiment where straw was imported and applied to soil that had been fallowed for 12 months before sowing the wheat than in the other two where the straw was incorporated following the harvest of a winter wheat crop. In the subsequent 4 years, incorporating up to 20 t straw/ha had no significant effects on grain yield but there were some significant effects on concentrations and uptakes of N, P and K, especially on the heavier textured soils. The effects on crop growth and yield that were detected in the first year on each site are tentatively attributed to decreases in available N representing that which was required to support the decomposition of the incorporated straw. The relative lack of significant effects in subsequent years seems to imply that a significant proportion of this N was remineralized relatively quickly, and thus available to support the decomposition of the straw that was incorporated in the second year and, after further recycling, in the years after that. Eyespot, caused by the fungus Pseudocercosporella herpotrichoides, was decreased by incorporating straw but there were few significant effects on other diseases. The results provide a generally reassuring message for farmers in suggesting that on most, if not all, soils there is little cause for concern about the consequences of incorporating even large amounts of wheat straw before sowing a further crop of winter wheat.

Experiments at three sites in 1993, six sites in 1994 and eight sites in 1995, mostly after oilseed rape, tested effects of previous fertilizer N (differing by 200 kg/ha for 1993 and 1994 and 300 kg/ha for 1995) and date of sowing (differing by about 2 months) on soil mineral N and N uptake by winter wheat cv. Mercia which received no fertilizer N. Soil mineral N to 90 cm plus crop N (‘soil N supply’; SNS) in February was 103 and 76 kg/ha after large and small amounts of previous fertilizer N respectively but was not affected by date of sowing. Previous fertilizer N seldom affected crop N in spring because sowing was too late for N capture during autumn, but it did affect soil mineral N, particularly in the 60–90 cm soil horizon, presumably due to over-winter leaching. Tillering generally occurred in spring, and was delayed but not diminished by later sowing. Previous fertilizer N increased shoot survival more than it increased shoot production. Final shoot number was affected by previous fertilizer N, but not by date of sowing. Overall, there were 29 surviving tillers/g SNS.

N uptakes at fortnightly intervals from spring to harvest at two core sites were described well by linear rates. The difference between sowings in the fitted date with 10 kg/ha crop N was 1 month; these dates were not significantly affected by previous fertilizer. N uptake rates were increased by both previous fertilizer N and late sowing. Rates of N uptake related closely to soil mineral N in February such that ‘equivalent recovery’ was achieved in late May or early June. At one site there was evidence that most of the residue from previous fertilizer N had moved below 90 cm by February, but N uptake was nevertheless increased. Two further ‘satellite’ sites behaved similarly. Thus at 14 out of 17 sites, N uptake until harvest related directly and with approximate parity to soil mineral N in February (R2 = 0·79), a significant intercept being in keeping with an atmospheric contribution of 20–40 kg/ha N at all sites.

It is concluded that, on retentive soils in the UK, SNS in early spring was a good indicator of N availability throughout growth of unfertilized wheat, because the N residues arising from previous fertilizer mineralized before analysis, yet remained largely within root range. The steady rates of soil mineral N recovery were taken as being dependent on progressively deeper root development. Thus, even if soil mineral N equated with a crop's N requirement, fresh fertilizer applications might be needed before ‘equivalent recovery’ of soil N, to encourage the earlier processes of tiller production and canopy expansion. The later process of grain filling was sustained by continued N uptake (mean 41 kg/ha) coming apparently from N leached to the subsoil (relating to previous fertilizer use) as well as from sources not related to previous fertilizer use; significant net mineralization was apparent in some subsoils.

Nitrogen-15 enriched ammonium sulphate was applied to micro-plots in a field in which two leguminous (white clover and peas) and two non-leguminous (ryegrass and winter wheat) crops were grown to produce 15N-labelled crop residues and roots during 1993/94. Nitrogen benefits and recovery of crop residue-N, root-N and residual fertilizer-N by three succeeding winter wheat crops were studied. Each crop residue was subjected to four different residue management treatments (ploughed, rotary hoed, mulched or burned) before the first sequential wheat crop (1994/95) was sown, followed by the second (1995/96) and third wheat crops (1996/97), in each of which residues of the previous wheat crop were removed and all plots were ploughed uniformly before sowing. Grain yields of the first sequential wheat crop followed the order: white clover > peas > ryegrass > wheat. The mulched treatment produced significantly lower grain yield than those of other treatments. In the first sequential wheat crop, leguminous and non-leguminous residues supplied between 29–57% and 6–10% of wheat N accumulated respectively and these decreased with successive sequential crops. Rotary hoed treatment reduced N benefits of white clover residue-N while no significant differences in N benefits occurred between residue management treatments in non-leguminous residues. On average, the first wheat crop recovered between 29–37% of leguminous and 11–13% of non-leguminous crop residues-N. Corresponding values for root plus residual fertilizer-N were between 5–19% and 2–3%, respectively. Management treatments produced similar effects to those of N benefits. On average, between 5 to 8% of crop residue-N plus root and residual fertilizer-N was recovered by each of the second and third sequential wheat crops from leguminous residues compared to 2 to 4% from non-leguminous residues. The N recoveries tended to be higher under mulched treatments especially under leguminous than non-leguminous residues for the second sequential wheat crop but were variable for the third sequential wheat crop. Relatively higher proportions of leguminous residue-N were unaccounted in ploughed and rotary hoed treatments compared with those of mulched and burned treatments. In non-leguminous residue-N, higher unaccounted residue-N occurred under burned (33–44%) compared with other treatments (20–27%).

Seed crops of the variety Estima were grown in each of 2 years using two planting dates, two harvest dates, two plant densities and two irrigation regimes to produce seed tubers which had experienced different cultural and environmental conditions. The effects of these treatments on tuber characteristics, sprout production and stem development in the ware crop were then determined in subsequent experiments using storage regimes of 3 and 10 °C. Time of planting the seed crop affected numbers of eyes, sprouts and above ground stems in the subsequent ware crop because environmental conditions around the time of tuber initiation appeared to alter tuber shape. Cooler, wetter conditions in the 7 days after tuber initiation were associated with tubers which were longer, heavier and had more eyes, sprouts and above ground stems. In contrast, the time of harvesting the seed crop did not affect tuber shape or numbers of above ground stems and there was no interaction with tuber size. The density of the seed crop had no effect on any character measured and irrigation well after tuber initiation did not affect tuber shape, numbers of sprouts or numbers of stems. Seed production treatments, which resulted in earlier dormancy break, were associated with tubers that produced more sprouts and above ground stems, in contrast to the conventional understanding of apical dominance. Storage at 3 °C gave fewer sprouts, a lower proportion of eyes with sprouts and fewer stems than storage at 10 °C. The major effects on stem production appear to result from environmental conditions at the time of tuber initiation of the seed crop and sprouting temperature.

Tetraploidy or the use of diploid genotypes with genes conferring high water-soluble carbohydrate concentrations are two mechanisms to increase the nutritive value of perennial ryegrass. This experiment compared the morphology, nutritive value and diurnal variation in water-soluble carbohydrate (WSC) concentrations of 56-day-old plants from six perennial ryegrass cultivars grown under controlled environment conditions. Three of these cultivars were diploid (Melle, Aurora and Cariad) and three were tetraploids (Meltra, Prospero and AberOnyx) which had been derived from the respective diploid cultivars. Two of the diploid cultivars (Cariad and Aurora) had previously been selected for high concentrations of water-soluble carbohydrates. The tetraploid cultivars had fewer (mean 59), larger tillers than the diploids (mean 83). However, with the exception of Melle and Meltra the dry matter yield of the diploid cultivars was not significantly different from their tetraploid derivatives. The effect of tetraploidy on WSC concentrations was dependent on the genetic background of the cultivars. Melle, which had not been previously selected for increased WSC, had a significantly lower WSC concentration than its tetraploid derivative, Meltra. However, tetraploidy did not further increase the WSC concentration in those cultivars previously selected for high WSC concentrations. WSC concentrations in the leaf of both Aurora and Melle rose by 65–70 g/kg throughout the photoperiod, suggesting that differences in the total WSC concentration of these cultivars were not due to any increase in the amount of carbon fixed by Aurora but rather due to differences in the allocation of carbon during growth and development. This experiment demonstrated that tetraploidy was not beneficial in improving the WSC concentration of perennial ryegrass when imposed on two diploid cultivars which had the genetic potential for increased WSC accumulation. However, tetraploidy significantly increased the WSC concentration and by implication the nutritive value of a cultivar derived from a perennial ryegrass cultivar with standard WSC concentrations.

At Shika in a subhumid environment of Nigeria, a 3-year study was carried out to select newly developed groundnut varieties for use in crop–livestock production systems. The study examined 11 groundnut varieties. Emergence time, plant stands at full emergence, forage and seed yields and yield components were examined. Whole plant samples were analysed for crude protein (CP) content. Varieties ICGV 87123 gave the lowest forage yield and cultivar M517-80I, the highest, with seven varieties recording forage yields above 5 t/ha. The CP content of forage was lowest (14·8%) for variety M576-80I and highest (21·6%) for variety M554-76. Mean seed yield (over 3 years) varied significantly from 0·73 to 1·68 t/ha. Only two varieties had mean seed yield >1 t/ha. The relationship between seed and forage yields was positive and significant (r = 0·529, P < 0·006). Varieties RMP 12, 88-80I and M517–80 were most promising for both forage and seed production.

Heat tolerance of groundnut (Arachis hypogaea L.) was evaluated under field conditions using physiological traits identified in a yield model [crop growth rate (C), reproductive duration (Dr) and partitioning (p)]. In 1991, 625 diverse genotypes were initially screened under irrigation during the hottest months (February to May). Subsequent tests consisted of 16 contrasting genotypes selected based on a combination of high pod yield and partitioning coefficient of >0· 50. Large variation was observed among the 625 genotypes for pod yield and physiological traits. C was a powerful factor influencing pod yield. Eight genotypes combining high pod yield and a partitioning coefficient greater than 0·6 were identified. These included two released cultivars (55–437 and 796) in the Sahel. Correlations between seasons were significant for p (r=0·84), but non-significant for pod yield (r=0·40), C (r=0·39), and Dr (0·36). Date of sowing and genotypes had significant effects on pod yield and C, but were slight on p and Dr. Pod yield of most genotypes declined by more than 50% when flowering and pod formation occurred when maximum temperatures averaged 40°C. The results revealed that estimates of p would be a more reliable selection criterion for identification of genotypes tolerant to heat than yield. Further research is suggested to maximize crop growth rate and partitioning of genotypes growing under supra-optimal temperatures.

Previous studies have demonstrated that protein sources which are primarily degraded in the rumen such as rapeseed meal or soyabean meal may be as effective as a less rumen degradable protein source such as fishmeal in supporting higher levels of animal performance in young steers fed on grass silage. However, the response to type of protein supplement is likely to be influenced by the composition of the basal diet. This study has examined the effect of supplementing silages prepared from early (EH) and late (LH) harvested grass with two protein sources of differing rumen degradability, rapeseed meal (RSM) and fishmeal (FM) or a mixture of the two (M), thus creating eight experimental diets of LH, LHRSM, LHFM, LHM, EH, EHRSM, EHFM and EHM. Silage was offered ad libitum and supplements were included at 100 g fresh weight/kg silage DM intake. The RSM and M diets were made isonitrogenous with FM diets by the addition of urea. Animals remained on diets for 18 weeks and liveweights were monitored for a further 13 weeks while the animals were at pasture. Dry matter (DM) intakes and liveweight gains were higher with EH than with LH silage (P < 0·001). Response to type of protein supplement was dependent on silage quality. On LH silage, higher intakes were noted on FM and M (82·4 and 82·8 g DM/unit metabolic liveweight/day, respectively) relative to silage only (75·8 g DM/unit metabolic liveweight/day) and this contributed towards higher liveweight gains (P < 0·01). Liveweight gains tended to be higher on LH silage supplemented with FM compared to RSM (0·76 v. 0·67 kg/day, respectively, P = 0·08). In comparison, on EH silage, relative to EH unsupplemented, the intake was highest on M (89·2 v. 96·6 g DM/unit metabolic liveweight/day), but liveweight gains were not significantly different between supplements. On turnout to pasture, those animals fed on silage alone exhibited compensatory growth (P < 0·025) with the result that those fed on LH silage only grew faster and achieved the same liveweight after 13 weeks at grass as those supplemented with RSM or M. There was a tendency for those fed on FM to maintain an advantage in liveweight after the period at pasture. On EH silage, at the end of the grazing period no significant differences in liveweight existed between the different supplements and on average were 23 kg heavier than EH silage unsupplemented. In conclusion, silage type (stage of harvest and quality) and protein supplementation influenced animal performance. On late harvest and poorer digestibility silage, there was some indication that feeding fishmeal was better than rapeseed but this was less evident on early harvest and higher digestibility silage. However, considering the price differential between these two supplements and small difference in animal performance it is concluded that rapeseed meal is as effective as fishmeal when used as a protein supplement for growing cattle fed on grass silage.

A summer lamb finishing experiment at Palmerston North, New Zealand compared the performance and health of weaned lambs grazing Aries HD or Yatsyn 1 perennial ryegrass (Lolium perenne). Aries HD ryegrass was originally selected for increased digestibility over summer and early autumn. Two groups of Romney×Suffolk lambs (15 per group) were rotationally grazed on each cultivar in a leader-follower sequence to assess both the nutritive value of the pastures and the alkaloid challenge imposed by the respective cultivar/endophyte (Neotyphodium lolii) associations. Herbage from leader pastures contained a higher content of ryegrass (600 v. 474±27·3 g/kg, P < 0·001) and a lower content of dead material (355 v. 479±34·2 g/kg, P < 0·001) than follower pastures. The in vitro organic matter digestibility coefficient of leader pastures was greater (0·62 v. 0·55±0·024, P < 0·05) and the neutral detergent fibre content lower (592 v. 631±11·4 g/kg, P < 0·005) than follower pastures. Consequently, the leader lambs had faster liveweight gains (92 v. 53±10·6 g/day, P < 0·0005) than the follower lambs. Aries HD and Yatsyn 1 cultivars were similar in sward composition, in vitro organic matter digestibility, neutral detergent fibre content and nitrogen content. Lambs grazing Aries HD had a higher herbage intake in late January than lambs grazing Yatsyn 1 pasture (0·95 v. 0·85±0·023 kg OM/day, P < 0·005). Overall, the liveweight gains of lambs grazing Aries HD and Yatsyn 1 were similar (71 v. 73±10·6 g/day, P > 0·7).

Grazing sequence and cultivar did not affect the concentrations of lolitrem B and peramine from herbage cut to ground level. However, serum prolactin concentration, which can indicate ergovaline intoxication, was lower in lambs grazing follower swards (181 v. 120±18·0 ng/ml, P < 0·005). Ergovaline concentration in Aries HD herbage was about half the concentration detected in Yatsyn 1 herbage (0·25 v. 0·49±0·050 mg/kg, P < 0·001). In addition, respiration rate, which can be an indicator of heat stress, was higher in lambs grazing Yatsyn 1 than Aries HD (77 v. 74±1·1 breaths per minute, P < 0·005). All lambs on all treatments had clinical ryegrass staggers from 10 February to 9 March. Lambs were removed from the experiment on 9 March. Both grazing sequence and cultivar affected the severity of ryegrass staggers. Staggers score was highest in Yatsyn 1 followers (4·4) and lowest in Aries HD leaders (3·1). Both grazing sequence and cultivar affected the alkaloid challenge imposed on lambs, resulting in differences in staggers severity, heat stress and performance of the lambs over the summer and autumn period.

A statistical model of the grazing preference of sheep is presented for the evaluation of spaced plants in small plots for plant breeding purposes. Plants are located randomly to reduce the effect of external factors on diet selection, and to differentiate between discriminatory and random grazing. Consistency of discrimination among grazings and sites (Massey University, New Zealand and INIA La Estanzuela, Uruguay) was tested. The statistical design and subsequent analyses considered all sources of variation to minimize error, and to separate genetic effects from environment effects. Clonal replicates were used to enhance error-control, and hence the precision of heritability estimates, as most characters are inherited quantitatively. Post-grazing leafiness is considered the best character to select and breed for animal preference in a red clover germplasm.

The present experiment was conducted to quantify the net fluxes of both free and peptide amino acids across the mesenteric and stomach portions of the portal-drained viscera (PDV) of three yak cows (172·3±18·6 kg, BW) fed a straw-concentrate diet at maintenance level. Yaks had been fitted with sampling catheters in the portal vein, mesenteric artery and mesenteric vein prior to its convergence with the gastrosplenic vein. Blood flow was determined by measuring the dilution of para-aminohippurate (PAH) infused constantly into a distal mesenteric vein. Amino acids in the deproteinized plasma were analysed before and after acid hydrolysis. The increased amino acids after acid hydrolysis were considered as peptide-bound amino acids (PAA). The fluxes of free amino acids (FAA) and PAA across PDV and mesenteric-drained viscera (MDV) were calculated as the product of venoarterial differences and plasma flow. Flux across the stomach viscera (SDV) was calculated as the difference between portal and mesenteric fluxes. Portal blood flow was 389 l/h or 2·32 l/h kg BW, of which 37% was contributed by the mesenteric vein. There was net appearance of a large quantity of PAA across PDV, which accounted for 92% of the total nonprotein amino acid flux. Net release of PAA and FAA in SDV accounted for 78% and 42% of the net release in PDV, respectively. These results suggest that in yaks, peptide possibly is the primary form of amino acid absorption, and that the stomach area probably is the major site of peptide absorption.