A method for investigating the thermoperiodicity of crop plants is described. On the basis of our experimental results and published data, crop plants were assessed to establish whether they were thermoperiodic or not. Tomato and maize were classified as thermoperiodic species. Cucumber, beans, peas, oats and wheat were not thermoperiodic. Strategies for climate control based on the estimation of optimum temperature are proposed. These can be used to minimize energy consumption and, together with other environmental treatments, could optimize the yield of glasshouse crops.

The consequences of selection for shorter, stiffer-strawed varieties that are less susceptible to lodging on the degradability of forage and straw obtained from cereal crops were investigated with particular reference to the characteristics of the basal internode where the mechanical stress is likely to be greatest. Quantitative measurements of tissue area, mean cell wall thickness, cell wall density and cellsize were made on two wheat cultivars, Riband (strong) and Norman (weak), and on two barley cultivars, Blenheim (strong) and Tyne (weak). The cultivars were selected for comparison on the basis of their straw strength in field trials.

At growth stage (GS) 59 in wheat (ear emergence complete) the neutral detergent fibre (NDF) content of the basal internode of Riband (74·6%) was lower than Norman (86·0%), and the NDF degradability (NDFD) of Riband (34·7%) was slightly greater than Norman (32·0%). No significant differences in lignin content were found between the wheat cultivars. In barley at the same growth stage, the NDF content of the basal internode of Blenheim (84·8%) was lower than Tyne (89·2%), and the NDFD of Blenheim (30·2%) was greater than Tyne (23·7%) but no significant differences in lignin content were associated with the difference in NDFD. At GS 32–37 (stem elongation) in barley the NDF content of the basal internode of Blenheim (81·5%) was also lower than Tyne (86·3%), but the NDFD of Blenheim (71·7%) was much greater than Tyne (42·8%). No significant differences in lignin content were associated with this large difference in NDFD.

The cultivars of wheat and barley less susceptible to lodging showed lower NDF content and higher in vitro degradability in the basal internode than the more susceptible cultivars. No evidence of differences in the extent of cross-linking by ether-bound ferulic acid was found in wheat, but stems of Blenheim barley showed evidence of a greater degree of cross-linking than in Tyne. The anatomical features of Norman wheat were consistent with stem weakness caused by thinner, smaller cells than the stronger Riband. However, in contrast, the anatomy of Tyne barley indicated that the straw may be too stiff, resulting in failure due to root lodging or brackling while the thinner more cross-linked cell walls of Blenheim may allow the stem to bend under load.

The relationship between the anatomical features, chemical composition and in vitro degradability of the stems was investigated using stepwise multiple regression. Thickness of sclerenchyma, thickness of epidermis and density of epidermis (area fraction of cell wall) were selected by the method of ‘backward elimination’ from an initial regression model to predict NDFD using all the anatomical features measured. Thickness of sclerenchyma was ranked first when the selected anatomical features were incorporated into a regression model with NDF and lignin content using the method of ‘forward selection’. Anatomical differences between varieties had an effect on degradability distinct from that due to the overall chemical composition. The results emphasise the contribution made by anatomical features to the stem degradability and lodging characteristics of cereals.

Starting with the F2 generation of a single-cross hybrid, a maize population was improved from cycle 0 (= F2) to cycle 4 by mass honeycomb selection and from cycle 5 to cycle 8 by pedigree honeycomb selection. Seven half-sib families were derived from cycle 8. The grain yield of these, their corresponding S1 lines, testcrosses with B73 and diallel crosses were studied. The results showed (i) that the seven half-sib families contained half the percentage of the load of deleterious genes present in the F2 generation, (ii) that four of them outyielded their corresponding single-cross hybrids, (iii) that they could constitute an open-pollinated variety, which could be used as a source population and (iv) that they revealed different patterns for general and specific combining ability. Honeycomb selection for grain yield was successful in favouring the existing additive genetic variation in the derived families.

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 +.

A field experiment was conducted at the experimental farm of the Central Soil Salinity Research Institute, Karnal, India during 1992/93 to evaluate the effects of rates and methods of manganese application on the yield and nutrition of wheat on a reclaimed and intensively cropped Mn-deficient sodic soil (pH = 8·7, exchangeable sodium percentage = 18 and DTPA-extractable Mn = 2·7 mg kg-1). There were eight treatments which consisted of a control (no Mn application), three rates of 25, 50 and 100 kg MnSO4. H2O ha-1 each either as a basal or a top-dressing at first irrigation or a foliar spray of 1·0% MnSO4.H2O at crown root initiation (CRI), tillering and jointing stages. Grain and straw yield of wheat increased significantly with increasing rates of Mn application. A foliar spray of Mn produced a significantly higher yield than 25 and 50 kg MnSO4. H2O ha-1 applied either as a basal or a top-dressing but similar to that from 100 kg MnSO4.H2O ha-1. Efficiency of Mn was higher with a foliar spray (82·6 kg grain kg-1 Mn) than with soil application (4·4–6·4 kg grain kg-1 Mn). Application of Mn increased its concentration in the crop but decreased Fe and Cu crop concentrations. Grain yield had a significant positive correlation with the Mn content of the grain (r = 0·72) and straw (r = 0·78). Grain yield was positively correlated with 1000-grain weight (r = 0·90). Recovery of applied Mn ranged from 28·1 to 33·0%.

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.

Measurements were made during 1987/88 on 20 winter wheat crops grown in Essex, four on each of five soil types – sandy loam, sandy silt loam, silt loam, calcareous clay loam and clay loam – where winter wheat, dried peas, winter faba beans or winter oilseed rape was the previous crop in 1986/87. The sites had a wide range of soil mineral N (SNS), 40–198 kg/ha N, as NH4 plus NO3, in the 0–90 cm soil profile. Optimum grain yield and fertilizer N could not be estimated but yields measured in the absence of fertilizer N enabled evaluation of the use of SNS on its own and the response to fertilizer N (187 ± 32 kg/ha). For crops receiving fertilizer N, each tonne of grain was associated with 35kg of total available N in the soil profile (SNS + fertilizer N); a little over 63% of this N was found in the above-ground parts of the crops at harvest. Fertilizer N requirement was predicted as:

Fertilizer N needed (kg/ha) = [35 × predicted grain yield (t/ha)]–SNS (kg/ha)

An arbitrary assumption of 8 t/ha grain for every site (fortuitously the same as the average of 8·07t/ha measured in crops given fertilizer N) showed that differences between added and predicted amounts of N differed by c. 30 kg/ha for only seven of the 20 sites, mostly because of large SNS or yields much less than 8 t/ha. Measuring SNS and using the formula would be justified in the majority of winter wheat crops, provided reliable yield estimates could be made in time.

Field experiments at Askov and Lundgaard Experimental Stations, Denmark, were carried out in 1987–91. Winter and spring applications of pig slurry at two application rates and an unfertilized treatment were combined with three rates of mineral nitrogen fertilizer; 15 treatment in all. Grain and straw yield, nitrogen content and nitrogen uptake of spring barley were measured at harvest. All main effects were significant, resulting in increasing yield and nitrogen uptake both when increasing the rate of mineral nitrogen fertilizer and slurry, and when slurry was applied in spring rather than in winter. The nitrogen content of the barley was affected by mineral nitrogen fertilizer application, and by the rate of slurry. The nitrogen efficiency of applied ammonia-N in the pig slurry was estimated by a quadratic polynomial yield response function and expressed relative to a reference function based on the application of mineral nitrogen fertilizer. The efficiency was estimated at 10 for spring-applied pig slurry. The value for winter-applied pig slurry was lower (0·6) and more variable. The efficiency of ammonia-N in spring-applied pig slurry decreased by 0·4/100 kg N/ha when supplementary mineral nitrogen fertilizer was applied at the same time.

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.

Winter wheat (Triticum aestivum L., cv. Hereward) was grown in the field within four double-walled polyethylene-covered tunnels along which near-linear temperature gradients were imposed at normal atmospheric or at an elevated CO2 concentration (c. 700 μmol mol−1 CO2) in 1991/92 and in a further experiment in 1992/93. Development was more rapid the warmer the temperature. In 1991/92 an increase in mean seasonal temperature of 3·5 °C reduced the duration from sowing to harvest maturity (the stage when grain moisture content reduced naturally to 15–18%) by c. 38 days, and reduced the duration from the double ridge stage to harvest maturity by c. 34 days. A similar difference resulted from only 1·6 °C warming in 1992/93. Although the range of mean seasonal temperatures differed between years, the relation between temperature and rate of development from sowing to harvest maturity was common to both years (base temperature, −0.8 °C; thermal time 2410 °C d). Carbon dioxide concentration had no effect on this relation or on that between temperature and the rate of development from sowing to the double ridge stage and from the double ridge stage to harvest maturity. Carbon dioxide enrichment increased tillering substantially in 1991/92; there were 200 more shoots m−2 at terminal spikelet formation in crops grown at elevated compared to normal CO2 (additional shoots were principally coleoptile tillers and those developing after tiller 2) and this difference was reduced to 100 shoots m−2 approaching harvest maturity (additional shoots remaining were those developing after tiller 2). In contrast, no effect of CO2 enrichment on tillering was detected at any stage of development in 1992/93. The number of tillers per plant at terminal spikelet formation was a linear function of main stem dry weight at this developmental stage; this relationship was not affected by year or CO2. As CO2 enrichment increased main stem dry weight in the first year only, when main stem dry weights at normal CO2 were only one half of those values determined in the following year, it is concluded that any benefit of increase in CO2 concentration to tillering in winter wheat may be greatest in those crop production environments where main stem dry weights at terminal spikelet are least and vice versa.

The use of environmentally induced genetic male sterile (EGMS) rice could alter the development of hybrid rice from a three-line system to a two-line system. It is critical for the utilization of EGMS rice to determine which are the main environmental factors influencing fertility changes. Fertility responses to photoperiod (P) and temperature (T) were studied in 101 EGMS rice lines under nine controlled regimes combining three photoperiods (15·0, 14·0 and 12·5 h)x three temperatures (30·1, 24·1 and 23·1 °C). According to the variance analysis of seed-setting data, 96% of the total EGMS lines studied could be divided into three types as follows: (1) photoperiod-sensitive genetic male sterility (PGMS) characterized statistically by significant (P < 0·05) P and P × T interaction effects but by a non-significant T effect on fertility, (2) thermosensitive genetic male sterility (TGMS) by a significant T effect, a non-significant P effect and by either a significant or a non-significant P × T interaction effect on fertility, and (3) photo-thermosensitive genetic male sterility (P-TGMS) by only a significant P × T interaction effect on fertility. Among the japonica EGMS lines studied, PGMS, TGMS and P-TGMS accounted for 32·3, 9·7 and 51·6%, respectively. However, among the indica EGMS lines, no PGMS lines were detected and most of them were TGMS or P-TGMS (61·4 and 35·7%, respectively). The results indicate that the selection of indica PGMS lines of rice might be very difficult. The availability of different types of EGMS rice in two-line system hybrid rice is evaluated and the selection of an ideal model of response to photoperiod and temperature for indica EGMS is discussed.

A field experiment was conducted at nine sites in England (1991–94) to compare six sown species of cover crop and natural regeneration in terms of nitrogen uptake and effect on response to applied N by a subsequent spring barley crop. The success and extent of cover crop establishment varied among sites and was insignificant in two. This may be associated with the relatively late sowing of the cover crops, the earliest site being sown on 27 August and the latest on 19 October. Dry matter (DM) yield of the sown cover crop at time of incorporation was related to sowing date, earlier sowing giving the higher yields. Maximum total DM yield and N uptake by the above-ground portion of cover crops were 1280kgDM/ha and 38 kg N/ha respectively. The extent of N uptake by the cover crops appeared to be related to the success of establishment rather than to the level of soil nitrate-N at the time of their sowing. Effects of cover crop incorporation on the subsequent spring barley were small. There was no evidence for any positive effect of the cover crop on N supply to the barley. In one trial, incorporation of forage rye significantly reduced grain yield of the barley by 0·7–1·2 t/ha compared to other cover crop species.

Two long-term field experiments were conducted on a clay soil near Carrickfergus, County Antrim from 1983 to 1993. The main experiment tested the effects of lime (0,4, 8 and 12 t/ha applied in 1983), N (160 and 320 kg N/ha per year as ammonium nitrate/calcium carbonate), sward type (permanent pasture and perennial ryegrass reseed) and initial soil pH (5·1 and 5·5) on the yield and composition of herbage for 10 years. The secondary experiment studied the interaction between lime (0, 4 and 8 t/ha applied in 1985) and N (80 and 160 kg N·ha per year) for 8 years. In both experiments the plots were fertilized three times each year for three cuts of herbage. In the main experiment, dry matter (DM) yield and N offtake over all 10 years depended little on initial soil pH. Over all cuts and years, DM yields of both sward types increased with lime. Responses peaked after 3 years and were largest with the first cut of the reseed at the lower rate of N fertilizer. Over the first 6 years after lime application, the average responses from the reseed at the lower rate of N fertilizer to 4, 8 and 12 t/ha of lime were 1·02, 1·85 and 1·65 t DM/ha per year respectively at the first cut. At the higher rate of N fertilizer, the response in DM yield of the reseed to lime averaged 0·91 t/ha at the first cut over the same period. In the last 3 years of the experiment, lime had no effect on DM yield even though soil pH ranged from 5·0 to 6·3 A significant response in N offtake due to lime only occurred at the first cut. Responses at the first cut averaged over all treatments were 3·5, 6·5 and 6·6 kg N/ha per year for 4, 8 and 12 t/ha of lime respectively. In the secondary experiment, responses to lime were again mainly at the first cut. There were few lime × N interactions in either experiment. Liming increased N availability either by increasing mineralization of soil N or by improving the uptake of ammonium and nitrate by roots. The effects of soil pH and Ca supply on these two processes are difficult to separate. All rates of liming at both N rates were cost-effective for the reseed, but only the lower rates of liming at 160 kg N/ha per year were cost-effective on permanent pasture. Current recommendations for liming grasslands should continue, particularly for swards reseeded with perennial ryegrass.

Crops of winter wheat (Triticum aestivum L. cv. Hereward) were grown within temperature gradient tunnels at a range of temperatures at either c. 350 or 700 μmol mol−1 CO2 in 1991/92 and 1992/93 at Reading, UK. At terminal spikelet stage, leaf area was 45% greater at elevated CO2 in the first year due to more tillers, and was 30% greater in the second year due to larger leaf areas on the primary tillers. At harvest maturity, total crop biomass was negatively related to mean seasonal temperature within each year and CO2 treatment, due principally to shorter crop durations at the warmer temperatures. Biomass was 6–31% greater at elevated compared with normal CO2 and was also affected by a positive interaction between temperature and CO2 in the first year only. Seed yield per unit area was greater at cooler temperatures and at elevated CO2 concentrations. A 7–44% greater seed dry weight at elevated CO2 in the first year was due to more ears per unit area and heavier grains. In the following year, mean seed dry weight was increased by > 72% at elevated CO2, because grain numbers per ear did not decline with an increase in temperature at elevated CO2. Grain numbers were reduced by temperatures > 31 °C immediately before anthesis at normal atmospheric CO2 in 1992/93, and at both CO2 concentrations in 1991/92. To quantify the impact of future climates of elevated CO2 concentrations and warmer temperatures on wheat yields, consideration of both interactions between CO2 and mean seasonal temperature, and possible effects of instantaneous temperatures on yield components at different CO2 concentrations are required. Nevertheless, the results obtained suggest that the benefits to winter wheat grain yield from CO2 doubling are offset by an increase in mean seasonal temperature of only 1·0 °C to 1·8 °C in the UK.

Soil surface moisture is a dominant factor influencing the establishment of surface sown seed, but its measurement is difficult. A cobalt chloride (CoCl2) saturated paper strip (20×5 mm) technique was developed as a cheap but sensitive indicator of soil surface moisture. The influence of soil surface moisture on the seedling survival of three oversown legume species, subterranean clover (Trifolium subterraneum L. cv. Karridale), strawberry clover (T.fragiferum L. cv. Grasslands Onward) and Caucasian clover (T. ambiguum Bieb. cv. Monaro) was investigated in a glasshouse and a field experiment at Palmerston North, New Zealand, between 1 October and 30 November 1993. Intact sods were sprayed with glyphosate, placed in plastic trays (420×300×50 mm) and transferred to the glasshouse or field. Three soil surface moisture treatments were imposed in the glasshouse. In the field trial, the plastic trays were buried flush with the soil surface in contact with the subsoil and exposed to natural wind and rainfall. Bare seed was oversown in a 20 × 20 mm grid and then pushed into the soil with a roller studded with metal rods to simulate treading by sheep. The low soil surface moisture treatment and the field trial had the lowest seedling survival. The main cause for this was low surface moisture caused by wind, which hindered radicle entry into the soil. Subterranean clover was less susceptible to low surface moisture and had better net seedling survival in all the treatments than the other two legume species.

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.

A split split-plot experiment was conducted in the 1986 and 1987 cropping seasons in three major yam-growing areas in southeastern Nigeria to assess the performance and yield stability of six cultivars of white yam (Dioscorea rotundata Poir). Location, fertilizer and cultivar, as well as some of their interaction effects, significantly affected tuber yields.

The best location for yam production, based on the overall performance of the cultivars, was the sub-humid Guinea savanna, followed by the humid forest-regrowth and then the transitional forestsavanna zone. Except for two cultivars, which performed best in their source locations, all other cultivars yielded best at a different location. Thus, at present, these cultivars are not grown in those areas to which they are best suited. This makes it desirable to test exogenous cultivars in new areas. In terms of yield stability, however, the two cultivars originating from the humid forest-regrowth area gave the most stable yields across the three diverse environments considered. Although they did not give the highest tuber yields at all the locations, their overall yields were above the mean yields forall the cultivars. The most suitable cultivars were recommended for each ecological zone, on the basis of the observed interaction effects.

Four field experiments were conducted over the 1992 and 1993 seasons (southwest monsoon seasons, June–October) in the warm subhumid tropical region on the west coast of the Maharashtra State, India. The objective was to investigate the effect of recycling limited amounts of rice straw (RS) (as a source of K and Si) integrated with the use of prilled urea (PU) and urea briquettes (UB) at 60 kg N/ha on the growth and yield of rainfed transplanted rice (Oryza sativa L.). The management practice, consisting of basal incorporation of RS (2 t/ha) integrated with deep placement of UB (one 2·1-g UB/4 hills) immediately after transplanting using a modified 20 × 20 cm spacing, produced a significantly higher grain yield (average increase of 1·3 t/ha) and straw yield (average increase of 1·1 t/ha) than did the RS practice integrated with two equal split applications of PU at the same N rate and hill spacing. The additional yields were attributed to the increase of total and productive tillers/m2 and panicle weight. The results indicate the potential of the integrated RS–UB management for increasing yields of rainfed transplanted rice in the warm subhumid tropical zone.