Methods of adjustment for two-dimensional spatial heterogeneity of grain yield were investigated for 224 UK cereal trials. The methods used row and column ‘block’ analysis of plot yields and neighbour analysis based on first differences of plot yields. In 36% of trial analyses for block models and 30% for neighbour models the average variance of variety differences was reduced by more than 10% compared with the better of the one-dimensional row or column models. Compared with complete blocks, 2-D block analysis had a mean efficiency of 153% whereas the conventional 1-D block analysis (by rows) had a mean efficiency of 127%. Similarly, 2-D neighbour analysis had a mean efficiency of 159% whereas the 1-D analysis had a mean efficiency of 137%. Recently, general statistical methods have been developed for two-dimensional design and analysis; their wider use should lead to major gains in the precision of variety trials.

Field experiments explored the relationship between canopy apparent photosynthesis (CAP) and grain yield and examined the effect of plant population density on CAP. Two cultivars of wheat were grown at five plant population densities in 1986 and 1987 in Taian, China. Measurements of CAP were made at intervals during the growth period by placing a large plastic-covered chamber over a 0·7 m2 segment of the canopy and measuring CO2 depletion with infra-red gas analysers for 1–2 min at c. 25 °C around noon when solar radiation was > 1100 umol/m2/s. Canopy respiration (CR) rates were measured by covering the whole chamber with a black screen in the daytime. Calculations of CAP and CR were made using the chamber volume, air temperature and changes in CO2 concentration over time and expressed on a land area basis.

Maximum values of CAP and CR were 4–6 g and 2–3 g CO2/m2/h, respectively, at the anthesis stage, decreasing with age during grain filling. The decrease was more rapid at the high than at the low population density. The difference in CAP between plant densities before booting and after anthesis could be attributed to reductions in leaf area index (LAI) and photosynthetic rate.

Grain yield also differed between plant population densities, the range being from 5250 to 7500 kg/ha in both years. Grain yield and 1000-grain weight were positively correlated with CAP during grain filling (r = 0·78 and 0·99, P < 0·01, 8 D.F.). Effects of plant density on CR were highly significant, but CR was not related to yield (r = 0·50).

The aim of this study was to identify a fluorescence parameter whose estimate could be used reliably for a drought tolerance test in durum wheat (Triticum durum). Twenty-five cultivars were grown in a glasshouse over two seasons (1987/88 and 1988/89) at Foggia, Southern Italy. Photochemical and non-photochemical quenching (qQ and qE), the half time of fluorescence decay (tP½) and the initial slope of fluorescence decay (ISPS) were measured on control and dehydrated pre-darkened excised leaves; qQ and qE were measured twice: first at 14 s after actinic illumination and second at the steady state.

No great difference in qQ and qE was apparent between control and dehydrated leaves at the steady state; however, at 14 s after illumination there was a decrease in qQ and in ISPS and an increase in tP½ in dehydrated leaves. The predictive capability of fluorescence parameters was assessed by comparison with a yield-based drought susceptibility index (DSI). The percentage decrease in qQ at 14 s showed the highest correlation with DSI (r = 0·75, significant at P < 0·001), so it may be considered a good indicator of drought tolerance in durum wheat. Results obtained at different developmental stages with different fluorescence levels (Fo, P and Fm) and parameters (qQ, qE and tP½) indicated that for maximum reliability the test must be applied at the vegetative phase.

Changes in leaf area index (LAI) of wheat are predicted by using information on daily heat units, atmospheric evaporative demand, water supply and nitrogen. The results of experiments on two different soils at Punjab Agricultural University Farm, Ludhiana, India from 1987 to 1990 showed that the rate and extent of leaf area development and its decline were dependent on the amount and pattern of water supply. Maximum leaf area index (LAImax) during the three years was found to depend on a combined effect of NO3-N in the 180 cm soil profile at sowing plus fertilizer N added. A relative growth factor (RGF) to scale cumulative water supply commensurate with crop growth was computed, which takes into account the combined effect of crop demand and supply of water and nitrogen from the soil. For adequately irrigated wheat, leaf area senescence could be predicted from cumulative potential evapotranspiration (PET). However, under droughted conditions, water supply, along with PET, also affected leaf area senescence. The dependence of wheat grain yield on LAImax in conjunction with water supply subsequent to attainment of LAImax was almost linear. It is concluded that, for adequately irrigated wheat, N availability at sowing and cumulative PET determines LAImax and the pattern of leaf development. Wheat grain yield is determined by LAImax and cumulative water supply from LAImax to maturity.

Effects of rhizobial inoculation and applied nitrogen on the utilization efficiency of N, P and K were studied in relation to the yield advantage in additive maize/mungbean intercrops at Los Baños, Philippines in 1988. Inoculation increased grain yield of both maize (Zea mays L.) and mungbean (Vigna radiata (L.) Wilczek). Yield of maize increased by 60% in the sole crop and 71% in the intercrop as the N application rate was increased from 0 to 90 kg/ha, with a corresponding decrease of 29–35% in the yield of the associated mungbean. Intercropping reduced mungbean yield by 35–57%; maize was less affected. Inoculation also improved the land equivalent ratio (LER). The highest LER (1·49) was obtained at 30 kg N/ha with inoculation.

Nutrient absorption by both maize and mungbean was reduced due to intercropping, mungbean being more affected than maize. The reductions in the N absorption efficiency of maize ranged from 4 to 37% and those of mungbean from 37 to 58%. Increases in N rate increased N absorption of maize but caused greater reductions in N absorption of mungbean. Reductions in P absorption by intercropped maize declined with increases in applied N and with inoculation. Inoculation, however, had a lesser effect on K absorption efficiency.

Land equivalent ratio analysis in terms of N, P and K utilization efficiency showed that the increase in LER over unity was due largely to a higher total uptake of nutrients by the component crops in the mixture than by the sole crops. The greater efficiency of intercrops than of the sole crops in converting absorbed nutrients to grains also contributed to the yield advantage.

Nine experiments were conducted in the south-east of Ireland on three contrasting soils over a 3-year period (1988–90) to test the effect of six cultivars at four rates of nitrogen on the grain yield and quality (ex-farm) of spring-sown malting barley.

Blenheim gave the greatest grain yield and lowest protein on average. Blenheim and Prisma had similar low protein values but Prisma gave significantly lower (P <0·05) mean grain yields than Blenheim at all three sites. Corniche gave significantly lower (P <0·05 to 0·01) grain yields than Blenheim in all nine experiments. Choice of cultivar had a considerable effect (<16%) on the yield and protein content of malting barley but season and soil type had a much larger effect (2–3 times greater).

The application of increasing increments of fertilizer nitrogen generally increased grain protein and screenings significantly (P <0·05 to 0·01) in all nine experiments but it did not always give increased grain yields. The levels at which nitrogen gave significant grain yield increases depended on season and soil type. Season and soil type had a much larger effect on grain yield and quality than nitrogen rate.

It was not possible to relate grain yield to specific climatic factors except on the light textured soil in 1990 when severe moisture stress in the early part of the growing season reduced grain yield by 32·5% compared with the previous 2-year average.

Leaf emergence, apex development stage, internode length and Zadoks principal growth stage 3 were measured over 3 years at several sites.

Internode elongation and Zadoks score were strongly related to the number of emerged culm leaves. The final length of the most basal internode was very variable and contributed to variation in the relationship between Zadoks stage 30 and the number of emerged culm leaves. Variation in the length of the basal internode was related to the final number of culm leaves. Most plants had six culm leaves but the number of leaves was affected by sowing date. In an experiment where sowings were made from September to March, stem elongation and Zadoks stage 30 started at a later stage of apex development in later sowings.

Recognition and prediction of culm elongation and number of emerged culm leaves is important for the application of growth regulator and fungicides. Combined with functions to predict the rate of leaf emergence and final number of leaves, the relationships described in this paper may enable Zadoks principal growth stage 3 and number of emerged culm leaves to be predicted.

A field experiment was conducted in 1990 and 1991 under intermediate deepwater conditions (15–50 cm) at Cuttack, India with two rice cultivars - Banaprabha, a semi-tall (130 cm), short duration (95 days), upland cultivar and Gayatri, a photosensitive, semi-dwarf (100 cm), lowland cultivar of long duration (170 days). The cultivars were direct-sown either in pure stands using 400 seeds/m2 at 20 cm row spacing or in mixed stands composed of alternate rows sown with 200, 300 or 400 seeds/m2 each at 10, 15 or 20 cm inter-row spacing. Mixed-row cropping of Banaprabha and Gayatri produced 17–21% higher grain yield than a pure crop of Gayatri. Panicles/m2 increased with higher seed rate and decreased with wider row spacing but a reverse trend was observed in panicle weight. Maximum grain yield was obtained at a row spacing of 15 cm but the effect of varying seed rates at each row spacing was non-significant. Gayatri produced up to 82% of its pure crop yield and contributed up to 70% of the total yield in the mixed crop system. Therefore, the yield advantage under mixed cropping was due to the late maturing cultivar benefitting from the increased area available after the harvest of the early cultivar. A crop stand using 200–300 seeds/m2 of each cultivar at a 15 cm row spacing was found to achieve the optimum productivity from the mixed cropping system.

A field experiment at Gudha Experimental Farm, Central Soil Salinity Research Institute, Karnal, India, in 1983/84 evaluated the effect of gypsum (12·5 t/ha, 50% of gypsum requirement of soil), pyrite (10·2 t/ha, equivalent to gypsum on a sulphur basis), farmyard manure (FYM) (30 t/ha), gypsum + FYM, pyrite + FYM and a control, with saline (ECiW 4·0 dS/m) and non-saline (0·4 dS/m) irrigation water on soil properties and yields of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) in a highly sodic soil (pH 10·5, 96% exchangeable sodium). Application of these amendments enhanced the yield of both crops significantly, irrespective of the quality of the irrigation water used. Soil properties and crop yields were improved in the following order: control < FYM < pyrite < gypsum < pyrite + FYM < gypsum + FYM. Irrigation with saline water resulted in significantly higher yields of both crops than irrigation with non-saline water. Decreases in soil pH and exchangeable sodium and increases in exchangeable Ca + Mg and infiltration rate were greater after rice than wheat in the rotation, particularly when non-saline water was used.

In intermediate deepwater conditions (0–50 cm) at Cuttack, India during 1990 and 1991, rice and dhaincha (Sesbania aculeata) were either mixed-sown in different arrangements (parallel lines and mixed broadcasting) in dry soil by the end of May or rice seedlings were transplanted in plots grown with pure dhaincha after the accumulation of water in the field by mid-July. Incorporation of dhaincha in situ after 48 and 54 days of growth added 60·8–65·2 and 72·9–76·9 kg N/ha in the mixed stands compared with 81·3 and 85·1 kg N/ha in the pure stand in 1990 and 1991 respectively. Although the growth of rice when sown simultaneously with dhaincha was affected initially due to the more vigorous growth and shading by the latter, tillering of rice increased after the incorporation of green manure following an increase in inter-row spacings. The performance of the direct-sown and transplanted rice was similar in 1990, when the water level rose relatively slowly, but in 1991 the transplanted crop yielded significantly less due to the sudden accumulation of water to higher depths (48 cm), resulting in greater mortality of seedlings at planting. However, the grain yield of both directsown and transplanted crops increased with dhaincha green manuring compared with the control (no application of dhaincha) and was equal to the application of 40 kg N/ha applied as urea fertilizer. The highest yield was obtained when rice and dhaincha were grown at a 2:1 ratio in 20 cm wide rows and the clonal tillers uprooted from the adjoining rice rows were planted in lines vacated by dhaincha. The yield was, however, equal to that from treatments where rice and dhaincha were grown in alternate rows at 15 cm spacing or mixed broadcasting. Increase in yield under green manuring was due to greater panicle weight, which was probably due to a continued supply of N following decomposition of organic matter added through dhaincha. Therefore, green manuring of direct-sown rice with dhaincha was beneficial for higher crop productivity under excess water conditions.

Pot and field experiments were conducted at the Faculty of Agriculture Arable Crops Farm, Kumasi, Ghana during the major rainy season to compare the agronomic efficiency of potassium in cocoa pod ash with that of muriate of potash and to determine the optimum rate of application of cocoa pod ash to maize (Zea mays L. cv. La Posta). Results from the two experiments indicated that the application of 90 kg N/ha and 67 kg P2 O5/ha did not increase shoot dry matter (DM) yield over the control. However, significant increases in DM yield over the control were obtained when N and P were applied together with 56 kg K2O/ha, demonstrating the complementarity of the major nutrient elements N, P and K. Shoot and root DM increased with increasing application of cocoa pod ash. Application of 140 kg/ha cocoa pod as (equivalent to 56 kg K2O/ha) produced the same DM and shoot potassium yields as 56 kg K2O/ha as muriate of potash. The optimum rate of application of cocoa pod ash was 280 kg/ha (112 kg K2O/ha).

The ability to survive severe summer water stress determines the persistence, and therefore autumn yield, of temperate grasses in the Mediterranean environment. In the island of Corsica, sward survival and changes in carbohydrate content were investigated over 2 years, in two contrasting populations of cocksfoot (Dactylis glomerata L.): KM2, an early-flowering population of Mediterranean origin and Lutetia, a late-flowering cultivar bred in North West France.

In Expt 1 (1987/88) three spring defoliation intensities were imposed. In Expt 2 (1989/90) three levels of water deficit were imposed under a rain shelter.

In spring, dry matter (DM) yields and water-soluble carbohydrate (WSC) concentrations in leaf bases were similar (20–35% of DM) for both populations. From June to September, WSC reserves tended to decline in Lutetia, whereas accumulation of WSC was maintained until August (45% of DM) in KM2. Fructans formed the major component, and therefore followed the same seasonal pattern, as total WSC. Contents of trisaccharide and sucrose increased in late summer as drought progressed. Contents of glucose and fructose were lower but increased in August or in September according to treatment.

In both field experiments during summer, KM2 had 50% more live tillers/m2 than Lutetia, possibly because it remained in positive carbon balance for a longer period. WSC levels in summer and regrowth in autumn were reduced both by intense defoliation in spring and by severe water stress in summer. On average, autumn yields of KM2 were five times greater than those of Lutetia and the recovery yields were closely correlated with fructan contents of leaf bases in summer (r = 0·80; P < 0·001).

The role of fructans and low DP-sugars as solutes in osmotic adjustment and as substrates for regrowth are discussed, and the differences between populations are analysed.

In 1990 and 1991, four rice cultivars – Utkalprabha, Panidhan, CN573–321–7–1 and Jaladhi–1 were sown in dry soil at the end of May and grown thereafter under semi-deepwater conditions (0–80 cm) at Cuttack, India. These crops were subjected to foliage cutting at the collar of the uppermost leaf on 1 September and/or on 1 October. The amount of foliage cut was greater in 1990 than in 1991 due to a relatively slower rise in water level in the initial stages of the experiments, which resulted in a more vigorous growth of the plants. The tall, rapidly elongating and floating deepwater cultivar Jaladhi–1 yielded the most foliage, followed by the relatively shorter cultivars CN573–321–7–1, Panidhan and Utkalprabha. However, the grain yield of CN573–321–7–1 was greatest and the effect of foliage cutting was least pronounced; whereas Jaladhi–1 gave the lowest grain yield which further decreased significantly when foliage was removed. Cutting in September had no effect on the yield of CN573–321–7–1, Panidhan and Utkalprabha, but the later cut in October had a detrimental effect, particularly when cutting was done a second time. Nevertheless, a single late cutting in October was not found to be harmful to the yield of the tall cultivar CN573–321–7–1 and the long-duration semitall Panidhan. Decrease in grain yield with two cuts of foliage was due to a reduction in the weight and number of grains/panicle as panicles/m2 and 1000-grain weight remained unaffected. The results suggest that foliage could be harvested for feeding cattle from the long-duration, tall and photosensitive rice cultivars without any adverse effect on grain yield under semi-deep lowland conditions.

The concentrations of water-soluble carbohydrate, N, nitrate-N, P, K, Ca, Mg and Na were determined in six plant species: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). Field crops of these species were grown at Aberystwyth in 1985,1986 and 1987. In 1985 and 1986 the rumen contents and faeces of lambs fed artificially dried diets of the different species were analysed for N, P, K, Ca, Mg and Na. The intake, apparent availability and, in 1986, retention of each element by the lambs on each diet were calculated.

The results illustrate the potential of dicotyledonous species to extend the range of concentration of some major elements beyond that normally found in temperate grasses. Chickweed was particularly high in P and K, dandelion in K and Mg, dock in Mg, ribwort in Ca and spurrey in Mg and Na. The apparent availability of the elements studied was as high in chickweed, dandelion and spurrey as in ryegrass. The apparent availability of N and P was lower in dock and ribwort than in ryegrass, possibly due to heat damage during drying. All five dicotyledonous species had a higher Mg concentration in herbage than ryegrass (c. 70% higher, on average) and all led to a higher Mg concentration in rumen contents than ryegrass (c. 70% higher, on average). Retention of Mg was three times as great, on average, in sheep fed dicotyledonous diets as in sheep fed ryegrass. The concentration of water-soluble carbohydrate was lower in the dicotyledonous species than in ryegrass. The concentration of nitrate-N was rather high in ribwort when harvested at a leafy stage in October. Dock was moderately low in nitrate-N, despite a rather high concentration of total N.

Yields from five of the plots on the Park Grass Continuous Hay experiment at Rothamsted, started in 1856, were examined to see if any long-term trends could be detected over the last 100 years. Three of the plots examined are unfertilized; two receive inorganic nutrients every year; all are harvested twice a year. In 1959 the harvesting procedure was changed: yields for the periods before and after this change were examined separately and together. On none of the three unfertilized plots was the slope of the regression of total yield (i.e. first and second cutscombined) on time significantly (P < 0·05) different from zero in either the 1891–1958 or 1960–1992 periods. On both the fertilized plots, there were significant declines in yield with time over the 1960–92 period, assuming that the effects of autocorrelation are sufficiently small to be ignored; there were no consistent changes between 1891 and 1958. There were some significant trends on the five plots when the two cuts were considered separately.

A linear regression model was fitted to the data in an attempt to separate the effects of meteorological variables (rainfall and sunshine hours over selected parts of the year) on total yield from possible long-term effects brought about, for example, by the increasing concentration of CO2 in the atmosphere. On four of the five plots this model accounted for between 12 and 21% of the yield variance in the pre-1959 period and between 45 and 63% after 1960. On the fifth plot, which received the highest level of N, the model accounted for 29% of the variance in the first period but only for 16% in the second period. When a linear trend with time was included in the model, this was not significant on any of the plots over the entire 1891–1992 period, although some significant trends appeared when the two periods were considered separately. The model was also fitted with the atmospheric CO2 concentration in place of the linear trend with time: again there were no consistent trends.

Neither changes in the concentration of CO2 in the atmosphere over the last century nor increasing inputs of combined N in rainfall or in dry deposition have had any detectable effects on yield in these plots.

In a clay loam at Rothamsted, inoculated with lucerne stem nematode (Ditylenchus dipsaci) and a leaf nematode (Aphelenchoides ritzema-bosi), lucerne herbage yields were increased on average by 17 and 59% respectively, in the first and second years of a 4-year experiment (1988–91), by carbofuran granules applied around the seeds at sowing in spring 1988. In seven-row plots over the 4 years of the experiment, 1·65 kg a.i./ha increased total yield as much as did 3·3 kg a.i./ha (11 and 12%, respectively). In four-row plots over the same period, 1·9 kg a.i./ha increased total yield by 9%. The cultivars Euver and Vertus, which are partially resistant to D. dipsaci, yielded 44·3 and 48·5 t dry matter/ha, respectively, whereas Europe and Vela, which are susceptible to the nematode, yielded less (36·3 and 28·6 t/ha, respectively). When sown in summer 1990 in four-row plots, cultivars Europe and Euver yielded larger crops in 1991 in plots given 1·2 or 2·3 kg a.i. carbofuran/ha in 1990 (on average 34 and 48%, respectively) than in untreated plots. As little as 0·6 kg carbofuran/ha increased the yield of cv. Europe in infested soil.

The stunting of lucerne plants, associated with D. dipsaci infestation, was greatly decreased by carbofuran, which prevented infestation of the first crop by D. dipsaci and A. ritzema-bosi. Stem nematode infestation of lucerne plots was adequately and quickly assessed by measuring the lengths of rows stunted by D. dipsaci. Other methods of assessment were laborious and no more reliable.

Field experiments were conducted for three consecutive years during 1988–90 at a research farm near the Indian Institute of Technology, Kharagpur, West Bengal, India to study the influence of organic and inorganic fertilizers on the performance of rice and fish in a dual culture system. Under waterlogged conditions the grain yield and dry matter of the rice variety CR1018 was increased both when inorganic N fertilizer (50 kg N/ha) was supplied or when a combination of organic (lOt FYM/ha) and inorganic N fertilizer (25 kg N/ha) were applied as compared with an organic fertilizer alone (20 t FYM/ha). The recovery of N as well as grain yield response per kg of N applied was also greater when inorganic N was applied. On the other hand, the growth of the fish species Java punti (Puntius javanicus) when grown alone (monoculture) and Catla (Catla catla), Mrigal (Cirrhinus mrigala) and Java punti (Puntius javanicus) grown together (polyculture) in the rice field was found to be superior when organic fertilizer was applied either alone or in combination with an inorganic fertilizer. The total number of phytoplankton species as food for the fish under organic manuring was more than under inorganic fertilization. In low-lying waterlogged situations (15–45 cm water depth), the total productivity could be increased by supplying the appropriate nutrition to both rice and fish in such dual culture systems.