Interplot competition in crop variety trials leads to biased estimates of variety differences. Modified alpha designs are proposed which aim to control competition by restricting the randomization so that adjacent varieties show similar competition effects. The designs are available in the computer program Alpha +.

Liming is often recommended to minimize the plant uptake of potentially toxic elements from sludgeamended soils. In outdoor experiments conducted during 1989–91 in a rural location, near Brentwood (UK), wheat, carrots and spinach were grown on soils from a wide range of sites previously amended with heavy applications of sewage sludge. The objective of these studies was to examine the effect of liming on the accumulation of sludge-borne metals in the crop plants. The results showed that liming the soils to pH 7 prior to sowing significantly reduced metal concentrations in carrots and spinach, although the reduction appeared to be greater for Cd, Ni and Zn than for Cu and Pb. The wheat crop was grown on soils which had been limed 2 years previously, and the average pH of these soils was 6·5 compared to a pH value of 5·95 in the unlimed soils. This comparatively small pH difference between limed and unlimed soils (6·50–5·95) generally had little influence on metal contents in wheat.

These results suggested that maintaining the soil at pH 7 is better than pH 6·5 for minimizing the accumulation of potentially toxic elements from soils which have received relatively high levels of sludge application over many years. The data for winter wheat suggested either that metal uptake into the grain was not sensitive to differences in soil pH or that a relatively small residual effect of past liming was not high enough to reduce metal uptake.

The effect of different rates (0–140 kg/ha) of nitrogen fertilizers on soil cyanobacteria and rice crop performance were studied in a rice-cropping system on an alkaline Fluvent soil at Valencia, Spain, during three consecutive crop seasons (1990–92). The results showed that the rice fields of Valencia favour the development of N2-fixing cyanobacteria. Nitrogen fixation varied during the cultivation cycle, reaching its highest values at the maximum tillering stage, 5–6 weeks after sowing, and showed a positive correlation with the abundance of cyanobacteria and a negative correlation with the amount of N fertilizers used. Grain yield increased with increasing amounts of N fertilizers up to 70 kg N/ha. N rates appeared to affect grain yield by causing variations in the number of panicles/m2. Leaf chlorophyll readings at the end of the tillering stage were positively correlated with the number of panicles/m2, suggesting that it could be a useful parameter for predicting productivity. There was a significant increase in the N uptake of the rice but a decrease in the apparent N recovery and Nuse efficiency of applied fertilizer N, with the application of increasing rates of N fertilizer. In all instances, except in plots fertilized with 140 kg N/ha, the amount of N removed by plants was significantly higher than that applied as N fertilizer. The differences were positively correlated with the values for N fixation, suggesting a significant contribution by N fixation to rice production. These results show that a rational use of biological N fixation, in combination with inorganic N fertilization, would permit the input of N fertilizers to be reduced by c. 50% without any significant loss of productivity and with an ecological benefit for the whole ecosystem.

Experiments were conducted in glasshouses at the Agronomy Department, International Rice Research Institute (IRRI), Philippines, in 1987 and 1988 to test the effects of small amounts of additional N applied at different times during the vegetative and reproductive phases of growth on rice yield components and on spikelet differentiation and survival.

The results showed that an additional 10 kg/ha of N fertilizer had the largest effect on maximum spikelet number when applied at growth stage (GS) 1·9 but was too low to sustain the survival of the differentiated spikelets. Applications after panicle initiation did not lead to an increased survival of spikelets. Foliar N application at GS 5·5 did increase spikelet survival.

The results confirm the role of limited N supply in restricting yields of rice. Altering the timing of N inputs seems unlikely to improve spikelet survival.

True dry matter digestibility, proportion of cell content, digestibility of cell wall, N and water-soluble carbohydrate were determined in eight related grasses in February, June and September in each of three years. In a separate experiment, true dry matter digestibility, proportion of cell content and digestibility of cell wall were determined in five plant parts of vegetative tillers of two grasses in February, April, June, August, October and December in each of two years.

Perennial ryegrass (Lolium perenne) was the most digestible grass and tall fescue (Festuca arundinacea) and Westerwolds ryegrass (Lolium multiflorum var. Westerwoldicum) were the least digestible. Italian ryegrass (Lolium multiflorum) was high in proportion of cell content, but not in digestibility of cell wall. Meadow fescue (Festuca pratensis) was high in digestibility of cell wall, but low in proportion of cell content. Perennial ryegrass and hybrid ryegrass were high, and tall fescue low, in both proportion of cell content and digestibility of cell wall. Ryegrasses were lower than fescues in concentration of N and higher than the fescues in water-soluble carbohydrate; ryegrass × meadow fescue hybrids were intermediate between the parent species in N and watersoluble carbohydrate.

Grass sampled in June and August was lower in both proportion of cell content and digestibility of cell wall than grass sampled at cooler times of year. Grass sampled in February was high in proportion of cell content and N, intermediate to high in digestibility of cell wall and intermediate in water-soluble carbohydrate.

Expanding leaf blades of perennial and Italian ryegrass were higher than expanded blades and sheaths in digestibility of cell wall and similar to expanded blades and higher than sheaths in proportion of cell content. Cell wall was less digestible in the tip than in the middle and basal portions of expanded leaf blades.

The effects of recommended application rates of the herbicide methabenzthiazuron (MBT) (2·5 and 4 kg ha-1) on vegetative growth, nodulation and N2 fixation in faba bean plants were studied in the field at Barcelona during 1990 and 1991. Nodulation, specific nitrogenase activity (SNA) of excised nodules, dry weight of plants and seed nitrogen content at harvest were compared in MBT-treated, hand-weeded (HW) and control plants. In 1990 the higher MBT application (4 kg ha-1) caused a decrease in nodulation and acetylene reduction activity (ARA) per plant during the mid-period of pod-fill, and also in vegetative growth, seed production and N content of seeds, whereas the lower rate (2·5 kg ha-1) did not have a significant effect on any of these factors. However, in 1991, growth and herbicide effects were different from those in the previous year. No inhibitory effect of MBT on nodulation, SNA or ARA per plant was observed and vegetative growth, seed production and N content of seeds were not significantly different from those of plants from HW plots. In 1991, both 4 kg ha-1 of MBT and the HW treatment caused a stimulatory effect on seed N recovery and yield compared to control plants. Rates of ARA per plant at late pod-fill were positively related to N recovery by seeds. These differences could have been due to the low rainfall in 1990, which may have permitted MBT to remain in the soil for a longer period and to inhibit N fixation and plant growth in the Vicia faba crop.

During a 3-year experimental period (between 1992 and 1995), residual effects on yields of subsequent crops of phosphorus applied either to soyabean or wheat, and on recoveries of the added P and changes in the available P, were studied in a soyabean–wheat cropping system on a typic haplustert very low in available P at Bhopal, India. Phosphorus was applied at rates of 0–52 kg P ha-1 (five treatments) to soyabean and 0–39 kg P ha-1 (three treatments) to wheat during the first year, and in the subsequent years the residual effects were studied in relation to fresh applications of 39 kg P ha-1 to each crop. The yields of soyabean and wheat were increased significantly by the application of P to each crop. Phosphorus applied to soyabean showed residual effects in two succeeding crops, whereas P applied to wheat showed a residual effect in only one succeeding crop. Phosphorus applied to soyabean was more efficiently utilized by the succeeding crops compared to that applied to wheat in the rotation. The recoveries of added P were greater with smaller rates of added P and greater in the first two residual crops. Olsen P in soil was adequate only in the first year and it fell below the critical limit in the subsequent two cycles of cropping. Cumulative P uptake by crops determined the levels of available P in the soil and soil test values declined with increase in cumulative P uptake over time.

The extent of variation in ratoonability was examined in a range of recently bred short-duration pigeonpea [Cajanus cajan (L.) Millsp.] genotypes in 1989/90, 1990/91 and 1991/92 at the ICRISAT Asia Center, Andhra Pradesh, India. Traits with which this variation could be associated were assessed. Differences in the total ratoon yield of two flushes were significant among the genotypes in each season. In a few genotypes, ratoon yield constituted 50% of the total yield, which could be as high as 5·6 t/ha. Total ratoon yield was positively correlated with leaf area index in the last 2 years of experimentation. The relationship of total ratoon yield to main crop yield was significantly positive in 1991/92 only. The results suggest that there is a large variation in ratoonability among short-duration genotypes and that high leaf area retention at main crop maturity appears to contribute substantially to this variation.

The effect of dwarfism on leaf number and size was investigated on six pairs of tall and dwarf nearisogenic lines of indeterminate autumn-sown white lupins (Lupinus albus L.). Dwarfism reduced mainstem height by 41% and first-order branch length by 22%. It also slightly decreased the number of leaves on the mainstem and first-order branches without affecting the time of flowering. Leaf size was not reduced. Logistic equations were used to analyse differences in the patterns of light interception by leaf canopies relative to thermal time from sowing during the growth of seven dwarf lines and three tall cultivars sown on different dates. The genotypes studied had long periods of low light interception during their early growth. No differences were found between most of the equation parameters for dwarf and tall genotypes. Only the proportion of light intercepted at flowering differed and this was explained by differences in flowering time. The dwarf character did not limit the ability of the crop canopies to intercept light. It is concluded that the character can be introduced into a wide range of genetic backgrounds without deleterious effects.

The Broadbalk Wheat Experiment at Rothamsted (UK) includes plots given the same annual applications of inorganic nitrogen (N) fertilizer each year since 1852 (48, 96 and 144 kg N/ha, termed N1 N2 and N3 respectively). These very long-term N treatments have increased total soil N content, relative to the plot never receiving fertilizer N (N0), due to the greater return of organic N to the soil in roots, root exudates, stubble, etc (the straw is not incorporated). The application of 144 kg N/ha for 135 years has increased total soil N content by 21%, or 570 kg/ha (0–23 cm). Other plots given smaller applications of N for the same time show smaller increases; these differences were established within 30 years. Increases in total soil N content have been detected after 20 years in the plot given 192 kg N/ha since 1968 (N4).

There was a proportionally greater increase in N mineralization. Crop uptake of mineralized N was typically 12–30 kg N/ha greater from the N3 and N4 treatments than the uptake of c. 30 kg N/ha from the N0 treatment. Results from laboratory incubations show the importance of recently added residues (roots, stubble, etc) on N mineralization. In short-term (2–3 week) incubations, with soil sampled at harvest, N mineralization was up to 60% greater from the N3 treatment than from N0. In long-term incubations, or in soil without recently added residues, differences between long-term fertilizer treatments were much less marked. Inputs of organic N to the soil from weeds (principally Equisetum arvense L.) to the N0–N2 plots over the last few years may have partially obscured any underlying differences in mineralization.

The long-term fertilizer treatments appeared to have had no effect on soil microbial biomass N or carbon (C) content, but have increased the specific mineralization rate of the biomass (defined as N mineralized per unit of biomass).

Greater N mineralization will also increase losses of N from the system, via leaching and gaseous emissions. In December 1988 the N3 and N4 plots contained respectively 14 and 23 kg/ha more inorganic N in the profile (0–100 cm) than the N0 plot, due to greater N mineralization. These small differences are important as it only requires 23 kg N/ha to be leached from Broadbalk to increase the nitrate concentration of percolating water above the 1980 EC Drinking Water Quality Directive limit of 11·3mgN/l.

The use of fertilizer N has increased N mineralization due to the build-up of soil organic N. In addition, much of the organic N in Broadbalk topsoil is now derived from fertilizer N. A computer model of N mineralization on Broadbalk estimated that after applying 144 kg N/ha for 140 years, up to half of the N mineralized each year was originally derived from fertilizer N.

In the short-term, the amount of fertilizer N applied usually has little direct effect on losses of N over winter. In most years little fertilizer-derived N remains in Broadbalk soil in inorganic form at harvest from applications of up to 192 kg N/ha. However, in two very dry years (1989 and 1990) large inorganic N residues remained at harvest where 144 and 192 kg N/ha had been applied, even though the crop continued to respond to fertilizer N, up to at least 240 kg N/ha.

Ceramic cup samplers were used to measure nitrate leaching from grass/clover pasture in Wales to which no N fertilizer had been applied and from a predominantly grass pasture receiving 100 kg fertilizer-N/ha annually. Annual leaching losses at individual sampling points, measured over a 3-year period between 1988 and 1991, ranged from the equivalent of < 0·1 to 226 kg N/ha. All data sets were positively skewed and in four out of six cases conformed to a log-normal distribution. The marked spatial heterogeneity was attributed to the uneven deposition of N in the excreta of grazing stock but variations in soil depth and hydrology may also have contributed. Particularly large losses occurred from those areas of the plots where sheep congregated. As a result of this heterogeneity, there were large standard errors associated with estimates of mean losses from the pastures as a whole. Overall losses ranged from 13 to 24 kg N/ha per year from grass/clover plots and from 10 to 13 kg/ha from fertilized grass plots. There was no consistent relationship between relative losses from the two types of pasture. The quantity of nitrate leached appeared to be independent of stocking rate, although there was a direct correspondence between the loss from grass/clover plots and the proportion of clover in the sward. Estimates of nitrate concentrations in drainage never exceeded 5·6 mg N/I for either sward.

Dietary calcined magnesite supplements of different particle sizes and temperatures of calcination were examined at Glasgow University Veterinary School in 1981. Balance experiments with wether sheep revealed that particle sizes < 75, 75–150, 150–250 and 500–1000 μm diameter of a feed-grade calcined magnesite all increased urinary output of magnesium to a similar extent but the apparent magnesium availability coefficient for the 500–1000 μm diameter fraction (0·03) was significantly less than for fractions of smaller diameter (0·17–0·23) (P < 0·01). A 1000–2000 μm fraction of fertilizer-grade material had an apparent availability of 0·18 but had the least effect on urinary magnesium output. Calcination temperatures of 800, 900 and 1100 °C significantly increased apparent availability (c. 0·46)compared with that for temperatures of 500 and 650 °C (c. 0·12) (P < 0·01), and significantly increased urinary output of magnesium. Losses of magnesium from these supplements incubated in the rumen of cows at grass in 24 μm mesh nylon bags showed some correlations with their apparent availability and urinary magnesium output. Solubility in molar ammonium nitrate showed some good correlations with urinary magnesium output but not with magnesium availability. Supplementation of a low magnesium diet given to lactating ewes with fine particle (< 75μm) calcined magnesite resulted in significantly greater increases in plasma magnesium concentration than when coarse particle material (500–1000 μm) was given (P < 0·05), but magnesites calcined at 650 and 800 °C induced similar changes in plasma magnesium.

Two grazing trials were carried out at Palmerston North, New Zealand using lactating red deer hinds in summer 1994 (Expt 1) and using weaner deer during the autumn, winter and spring of 1993 (Expt 2), to compare the feeding value of chicory (Cichorium intybus) and perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) pasture for increasing the growth of deer calves. Red deer and hybrid (0·25 elk; 0·75 red deer) calves were used in both experiments. Experiment 2 concluded with slaughter at the end of spring, when the deer were c. 12 months old. In both experiments, animals were rotationally grazed on either pasture or chicory with DM allowances being 12 kg DM/hind per day (Expt 1), and 6, 6 and 7 kg DM/head per day during autumn, winter and spring respectively (Expt 2).

Perennial ryegrass comprised 62% of pasture on offer in Expt 1 and 78–90% in Expt 2, whilst chicory comprised 90–92% of forage on offer in both experiments. Relative to pasture, chicory had a higher ratio of readily fermentable: structural carbohydrate and had higher organic matter digestibility (OMD) in summer and autumn but not in spring.

Deer grazing chicory had higher voluntary feed intake (VFI), bite weight, liveweight gain (LWG), carcass dressing percentage and carcass weight and much shorter ruminating time than deer grazing pasture. Hybrid deer grew better than red deer and there were forage × genotype interactions in Expt 2, with LWG and carcass weight of hybrid deer being much greater when grazed on chicory. Carcass weight for red deer and hybrid stags was 63·2 and 73·0 kg when grazed on chicory and 56·6 and 57·0 kg when grazed on pasture. Grazing chicory advanced the date of first-cut velvet antler by 28 days and increased the weight of total harvestable (first-cut + regrowth) velvet antler. It is concluded that grazing chicory increased carcass weight, especially in hybrid stags with increased growth potential, and increased velvet antler production. This was achieved by increased VFI in all seasons and increased OMD of chicory in summer and autumn relative to deer grazing pasture. Further research is need to determine the efficiency of rumination on particle size breakdown and to measure rumen outflow rate in deer fed chicory.

Two experiments (E1 and 2) were carried out in Northern Ireland in 1988/89 to examine the effects of a wide range of supplementary protein intakes given with grass silage-based diets on the performance and carcass composition of beef cattle, and to compare diets based on silage and dried forage. The five treatments used consisted of grass silage offered ad libitum and supplemented with 2·5 kg dry matter (DM) of barley-based concentrates containing (1) zero, (2) 0·2, (3) 0·4 and (4) 0·6 extracted soyabean meal and (5) artificially dried grass and hay supplemented with 3·3 kg concentrate DM. Experiments E3 and 4 were carried out in 1991/92 to examine the responses in ration digestibility, silage intake and animal performance to supplementary protein in relation to the requirements recommended by the United Kingdom Metabolizable Protein System. The two treatments consisted of grass silage offered ad libitum and supplemented with 3·2 kg DM of (1) barley and (2) 0·8 barley and 0·2 soyabean meal. The silages used were well preserved, containing on average 200 g DM/kg; 143 g crude protein (CP)/kg DM; 79 g ammonia-N/kg total N and 734 g digestible organic matter/kg DM. The cattle were castrated males of medium to late-maturing breed type and were initially 13 months old and 396 kg liveweight. Increasing protein intake did not affect ration digestibility, silage DM intake or animal performance in any of the four experiments, despite the fact that the effective rumen degradable protein (ERDP) intakes in the diets supplemented with barley alone were only 80–85% of ERDP requirements. However, increasing protein intake tended to increase carcass fatness in all experiments, the effect being significant (P < 0·05) for the lipid concentration in the M. longissimus dorsi muscle in E1 and 2. Offering the dried forage-based diet rather than an isonitrogenous silage-based diet did not affect carcass fatness. It is concluded that supplementing well preserved grass silages with mixtures of barley and soyabean meal, rather than with barley alone, did not affect ration digestibility, silage intake or animal performance but tended to increase carcass fatness, especially marbling fat, despite the fact that ERDP intakes for the diets with the lowest protein concentration were only 80–85% of requirements given by the United Kingdom Metabolizable Protein System.

An experiment was conducted at Palmerston North, New Zealand, to determine the effect of condensed tannins (CT) on the true and apparent digestion of methionine and cysteine in the small intestine (SI) of sheep fed fresh Lotus comkulatus. The lotus contained c. 30 g total CT/kg dry matter (DM) and was fed hourly to sheep in metabolism crates. Four sheep were prepared with rumen and abomasal cannulae which enabled the indigestible liquid phase marker, chromium ethylene diamine tetra-acetic acid (Cr-EDTA), to be infused into the rumen to estimate digesta flow. True digestibility of plant methionine and cysteine in the SI and their site of absorption in the SI were determined from 35S-labelled L. corniculatus homogenate continuously infused into the abomasum. After 9 h infusion of the 35S-labelled lotus homogenate, the sheep were slaughtered and digesta samples were taken at intervals along the small and large intestines. The effect of CT was determined by comparing two control sheep (CT-acting) with two sheep given a continuous intraruminal infusion of polyethylene glycol (PEG, MW 3500) to bind and inactivate the CT.

The CT reduced the true digestibility of plant methionine (0·72 v. 0·88) and cysteine (0·65 v. 0·81) in the SI relative to sheep receiving PEG. Condensed tannins also appeared to alter the site of digestion of both [35S]methionine and [35S]cysteine in the SI, and increased the flux of both amino acids in the mid and latter thirds of the SI. CT did not affect the apparent digestibility of total methionine (0·82 v. 0·84) in the SI but reduced the apparent digestibility of total cysteine from 0·77 to 0·66. In control sheep CT increased the abomasal flux (as a proportion of eaten) of total digesta methionine (0·88 v. 0·76) and total digesta cysteine (0·74 v. 0·62). The apparent absorption of total methionine (plant + microbial + endogenous) was increased by the action of CT (0·72 v. 0·63 g/g eaten) but was similar for total cysteine (0·49 v. 0·48 g/g eaten) in both groups. It was concluded that CT reduced the true digestibility of plant methionine and cysteine in the SI. However, it was calculated that the action of CT actually increased the total amounts (g/g eaten) of plant methionine and cysteine absorbed from the SI, due to its effect in increasing abomasal flux.