No abstract

Urea-treated whole-crop wheat harvested at growth stage (GS) 87 that was either unprocessed (U) or processed (P) by the forage harvester, and cut at one of two heights to produce a long straw (L), or short straw (S) forage, was offered to 44 Holstein-Friesian dairy cows for 14 weeks according to a 2 ✕ 2 factorial design. Whole-crop wheat (WCW) was mixed 2: 1 on a dry-matter (DM) basis with grass silage and all animals received 8·5 kg/day of concentrate and 2 kg/day of rapeseed meal. Increasing the cutting height at harvest increased the starch content in the forage from an average of 356 to 419 g/kg DM and decreased neutral-detergent fibre levels from 422 to 337 g/kg DM. Forage intake (grass silage and WCW) was higher in cows given the unprocessed compared with the processed forages (13·7 v. 12·5 kg DM per day for treatments U v. P respectively; P < 0·05) and tended (P < 0·08) to be higher in cows given the long compared with the short straw forages. Neither processing, nor alteration of cutting height, had a significant effect on milk yield (kg/day). However, milk fat content decreased (P < 0·05) with increasing cutting height (41·9 v. 37·0 g/kg for the main effects of L v. S respectively) whilst body condition score was lower (P < 0·05) in cows given the long compared with the short straw forages (2·6 v. 2·8 respectively). Plasma glucose levels were higher (P < 0·05) in animals receiving the short compared with long straw forages (3·52 v. 3·34 mmol/l respectively) whereas β-hydroxybutyrate decreased (P < 0·01) with increased cutting height. The average digestibility of starch in the total ration was higher (P < 0·001) in cows given the processed compared with the unprocessed WCW (0·96 v. 0·88 respectively). Assuming a constant apparent digestibility of starch in the other food components resulted in a WCW starch apparent digestibility of 0·87, 0·97, 0·80 and 0·96 for forages LU, LP, SU and SP respectively (P < 0·001). The results indicate that processing at harvest significantly increased the digestibility of starch in WCW and that cows responded to this higher nutrient content by decreasing forage intake. Increasing the cutting height at harvest decreased milk fat content (g/kg) and yield (kg/day) and increased body condition score.

A field experiment was carried out at Harper Adams in Shropshire to investigate the effect of supplying the spring N application to winter wheat as different proportions of urea as a solution, rather than as conventional soil-applied solid urea, on N recovery in the above-ground crop, autumn soil mineral N and nitrate leaching over the subsequent winter. A solid ammonium nitrate treatment was also included to represent alternative commercial practice to solid urea. Treatments were repeated on the same plots over the 3 years 1992, 1993 and 1994. N recovery was measured in all 3 years by difference in N uptake between fertilized and unfertilized plots, and in 1993 for selected treatments, N was applied as "&N-labelled fertilizer to determine direct uptake of fertilizer N in the crop and soil. Both urea sprays and solid soil N applications were labelled with "&N. Urea sprays were split over several days to reduce scorch, whereas solid fertilizer was applied as a single dressing. For some urea spray treatments, apparent N recovery in the above-ground crop in 1992 and 1994 was less compared with soil-applied N treatments. These urea spray treatments were applied in the morning rather than the evening, and gaseous losses, most likely by volatilization, are suggested. In 1992 application of a large proportion of N as urea sprays, such that application of some N as urea solution was delayed to around GS 37, was associated with an increase in physiological N use efficiency. In 1993, there was no difference in direct or apparent recovery of fertilizer N in the crop or soil for N applied as ammonium nitrate, solid urea or as urea sprays. Mean nitrate concentration in the drainage water at 1 m was elevated for all N treatments in all years, but only in 1992 did nitrate concentration and leaching loss decrease with increasing proportion of N applied as urea sprays. It may therefore be possible to reduce gaseous losses by application of urea sprays under cool conditions in the evening and exploit the increased physiological N use efficiency for urea sprays applied later, such that total fertilizer N applied and N losses are reduced.

The effect of rate of substitution of processed, urea-treated whole-crop wheat (pWCW) for grass silage on intake, performance and whole-tract digestibility was evaluated using 44 dairy cows. Cows received 10.5 kg of concentrates per day and one of the following forage mixtures (dry matter (DM) basis): grass silage alone (W-0); 0.75 grass silage, 0.25 pWCW (W-25); 0.5 grass silage, 0.5 pWCW (W-50) or 0.25 grass silage, 0.75 pWCW (W-75). Forage DM intake increased linearly with inclusion rate of pWCW from 9.7 kg DM per day in cows fed W-0 to 14.6 kg DM per day in W-75. By contrast, milk and protein yield (kg/day) were higher (P , 0.05) in cows receiving W-25 compared with W-0, but there was no effect (P . 0.05) of treatment on fat yield (kg/day). From week 11 of the experiment onwards, body condition score increased with rate of inclusion of pWCW ( P , 0.05). Whole-tract apparent digestibility of organic matter (OM) and fibre (kg/kg), decreased linearly with rate of inclusion of pWCW. Assuming a constant digestibility of starch in the other diet components, the apparent digestibility of starch in pWCW was 0.95 kg/kg and was not affected by rate of inclusion (P . 0.05). Four continuous culture vessels were used to determine the effect of rate of inclusion of pWCW on ruminal metabolism in four periods, each of 14 d duration with sampling conducted on days 9 to 14. Vessel ammonia concentration increased linearly ( P , 0.05) with rate of inclusion of pWCW whilst mean pH tended (P ¼ 0.06) to decrease. The ratio of acetate to propionate increased from 2.5 in vessels receiving W-0 to 3.2 in those receiving W-75 (P , 0.001). There was no effect (P . 0.05) of treatment on digestibility (g/g) of OM, fibre or starch or microbial protein flow (g/day). It is concluded that forage DM intake increased linearly with rate of inclusion of pWCW, but there was no further improvement in milk yield from inclusion rates above 0.25 of the forage DM, with body condition score increasing instead. Increasing the inclusion rate of pWCW resulted in a more ketogenic volatile fatty acid profile but did not affect the efficiency of microbial protein synthesis when determined in vitro.

Supplying a proportion of the N requirement of a wheat crop via the foliage would potentially reduce immobilization of fertilizer N in the soil organic matter and N losses by leaching or denitrification. A field experiment was carried out at Harper Adams in Shropshire to investigate the effect on crop yield of supplying the spring N application to winter wheat as different proportions of urea as a solution rather than as conventional soil-applied urea, and to determine the physiological basis of any yield differences. A solid ammonium nitrate treatment was included to represent alternative commercial practice to solid urea. Treatments were repeated on the same plots over the 3 years 1992, 1993 and 1994. Solid fertilizer was applied as a single dressing, whereas urea sprays were split over a number of days to reduce scorch. Nitrogen as urea sprays produced similar grain yields to N applied conventionally to the soil as solid ammonium nitrate or urea, but effects on above-ground dry matter production and harvest index depended on the time of application. Application of a large proportion of N as urea sprays, such that some of the N as urea solution was applied later in relation to crop development, produced less above-ground dry matter, but compensated by increasing harvest index. It is concluded that application of N as urea sprays could be successfully used to substitute for soil-applied N fertilizer at stem extension in winter wheat without loss of yield. Extra application costs, however, are likely to outweigh any efficiency or environmental benefits, except where applications of solid N are made to dry soils.