Regression analysis, stability variance method, and the genotype-grouping technique were used to investigate the relative yield stability of 20 soyabean genotypes, grown in 12 diverse environments in Malaysia in 1978. With the regression analysis, four genotypes were observed to be unstable for grain yield; however, for the remaining 16 genotypes with non-significant regression coefficients, a substantial proportion of the g × e interaction was non-linearly related to the environmental indices. With the second and third methods less than half of the genotypes turned out to be stable for grain yield. Generally, for some genotypes, the stability classification was the same for all three methods.

The effects of rootstock on tree development, leaf nutrient levels and yields of two old-clone lemon cultivars, Eureka and Villafranca, were studied. The largest canopy development and yields were obtained on Alemow and Volkameriana; red rough lemon failed due to foot rot; Rangpur lime trees were severely stunted; and Citremon induced high chloride and relatively low boron contents in the leaves.

The relation between some growth parameters in polybag oil palm nursery seedlings were assessed. ‘Non-destructive’ parameters such as leaf number, seedling height and girth were highly and positively correlated with one another and with the dry weight of seedlings. Amongst the ‘destructive’ parameters only leaf area, height/weight ratio and fresh weight were positively correlated with dry weight. The Leaf Area Index was poorly correlated with other parameters examined. The relevance of these findings to the selection of oil palm seedlings for transplanting into the field is discussed.

Six products possessing suitable physical properties as fluid carriers for pre-germinated seed were assessed for their effects on seedling emergence. Both glasshouse and field experiments measured the carriers' performance on eight crop species at varying extrusion rates and under different environmental conditions. Synthetic clay or polyacrylate increased seedling emergence by 10% compared with the sodium alginate control. Seedling emergence was least affected by moisture stress when synthetic clay was used as the carrier.

Studies of the effects of age on yield components and nutrients status of Celosia argentea cultivars showed the highest crude protein content, total vitamin C and leaf/stem ratio in leaves harvested 5 to 7 weeks after sowing, but the highest total marketable and edible yields, as well as total crude protein, 15 weeks after sowing. The narrow-leaved local cultivar gave higher crude protein per cent and vitamin C than the broad-leaved one, but its yield of edible leaf was lower. Breeding potentials of the cultivars were highlighted.

The yields of four potato varieties (two old and two new) in trials and in agriculture were compared. The six possible paired comparisons of means and of variety-on-variety regressions showed genotype–environment interactions. Trials and agricultural data agreed rather poorly as to both means and regressions, suggesting that further studies are desirable, in diverse crops, of the ability of trials to predict agricultural yields.

Dry matter produced and allocated to the tuber and aerial portions of yam plants (Dioscorea spp) were studied over 3 cropping seasons in the moist forest region of Nigeria, in an attempt to relate dry matter accumulation to vegetative maturity in the crop. The effect of duration of growth of yam on post-harvest dormancy was also studied. Cultivars differed both in the total amount and period of growth when most dry matter was accumulated. A higher proportion of dry matter was allocated to tubers in lower-yielding than in higher-yielding cultivars. It appears that a yam tuber is ‘mature’ almost as soon as it is formed.

A range of legumes was evaluated in North-east Thailand for dry season forage production on stored moisture following harvest of the paddy rice crop. Crotalaria juncea (sunnhemp) and Lablab purpureus (lablab) produced the best dry matter yields of 1950 and 2020 kg−1 ha respectively on a cultivated paddy field without further fertilizer. Stored moisture was adequate for these two but growth of other species was poor, especially on plots that received no prior cultivation. In pot experiments, sunnhemp did not respond to either nitrogen application or Rhizobium inoculation, indicating that native strains were effective for nitrogen fixation. Lablab responded to both treatments and gave a 55% dry matter response to inoculation with Rhizobium in the field.

Five types of mulches (black plastic, stone chippings and three types of grass) and a control were used on young clonal tea plants following transplanting. Soil temperature differences were observed in the first two years but disappeared when the tea canopy had developed to cover over 40% or more of the soil surface. Stem diameter, yield (during the first two years) and total dry matter production were positively correlated with soil temperatures over the range 14–21°C. Beneficial effects of raising soil temperature by black plastic mulch were short-lived, but the detrimental effect of reducing temperature by grass mulches was more severe and long lasting. Grass mulches induced shallow rooting, as a result of which the tea was more susceptible to drought.

Results clearly demonstrate that Crotalaria juncea (sunnhemp) is well adapted to the dry season paddy environment; peak dry matter production was 3170 kg ha−1 in a field experiment with rows 30 cm apart and 100 kg−1 ha of seed. A pot experiment gave yield responses of 179 and 16% to P and S application respectively but there was no response to fertilizer in the field. Cultivation increased DM production in one experiment from 86 to 1590 kg−1 ha, attributed to a reduction in bulk density from 1·65 to 1·19 g cm−3. This effect was not fully substantiated in a second experiment on a coarser soil, where good DM production of sunnhemp was achieved even on broadcast uncultivated plots. The toxicological implications of using sunnhemp as a forage legume are briefly discussed.

Variation in the growth of young vegetatively-propagated tea in the nursery was studied. Erect shoots grew more vigorously, furnishing cuttings which rooted better and produced stronger plants than those from the weaker, inclined shoots. When erect shoots were artificially inclined they showed reduced terminal bud activity and shoot growth, while inclined shoots artificially erected commenced bud activity and made growth like naturally inclined and erect shoots respectively. Pruning adequately fertilized mature tea bushes at 40 cm above ground level produced vigorous shoots and at 6–8 months furnished more acceptable cuttings that produced better plants, while non-pruned bushes produced less suitable shoots and cuttings. Young unpruned plants produced weak shoots with fewer and poorer cuttings. The practical implications of these findings are discussed.

On unlimed Malaysian peat (pH 3.5), flue-cured tobacco produced negligible leaf yields and showed no response to urea. Liming up to pH 5.25 (32 t/ha lime) linearly increased leaf yield. Tobacco responded linearly without reduced leaf quality to 90 k/ha N at pH 4.01 (8 t/ha lime), but to 45 kg/ha N at pH 4.40–5.25 (16–32 t/ha lime), higher N rates at the respective liming levels producing leaves of lower quality. The optimum rates of P and K for flue-cured tobacco appeared to be 26 and 186 kg/ha respectively, with linear responses up to those rates.

N, P and K fertilizers improved mulberry leaf, stem and fruit yields on peat, the optimum rates being 100 kg/ha/yr N, 25 kg P and 62·5 kg K, with further leaf responses to N and K if applied together in the ratio of 3:2. Harvesting every 2 months at 60 cm height gave better yearly leaf yields than cuttings 3–12 months apart, but annual stem yields were not affected by harvesting frequency and fruit yields were optimum when plants were cut at intervals of 5–6 months. Harvesting quarterly at 60 cm produced better leaf and stem yields than cutting lower (15 and 30 cm) or higher (100 and 180 cm). Two Thai cvs (Noi I and Mii) were female-sterile but the Local Malaysian produced fruits.

High plant populations caused a reduction in pod set and consequently in seed yield. Removal of axillary branches reduced the average weight of seed and percentage seed oil on primary racemes, indicating transport of photosynthate from branch leaves to storage sites in pods on primary racemes. Debranching at low densities was also associated with premature senescence of leaves and desiccation of immature pods, suggesting that branch removal need not have an exclusively simple nutritional basis. High canopy density reduced oil content, and seeds borne on primary racemes had lower oil levels than those on axillary branches.

Five field experiments studied the effects of high planting densities, ranging from 83,000 to 667,000 seeds/ha, on eleven soyabean cultivars. Germination rates ranging from 32 to 100% and averaging 76%, resulted in actual plant densities of 45,000 to 296,000 plants/ha. Bean yields of the four shortest and earliest-maturing (64–67 days) cvs (Wakashima, Shi-shi, Palmetto and Tai Tah Kaoh Siang 58) increased with increasing density, producing highest yields at the highest plant densities investigated (222,000–286,000/ha) but 7 taller cvs, maturing in 80–126 days (P2, C13, C21, P4, D5, T10 and C28), produced reduced yields with increasing density, the lowest densities investigated (45,000–83,000 plants/ha) giving the highest bean yields.

Soil moisture content and plant water status of young clonal tea plants were affected differently by five different types of mulches (black plastic, stone chippings and three types of grass) when compared with a control without mulch. During prolonged droughts, soil moisture content was generally highest under Napier grass and black plastic but any type of mulch was better than no mulch in conserving moisture to 90 cm depth. Tensiometer data at the onset of rains after an unusual prolonged dry season suggest that the infiltration was fastest under grass mulches. After four years of continuous application grass mulches had significantly most effect on water holding capacity, but induced shallow rooting systems, which made the mulched tea more susceptible to drought.

In Ghanaian cocoa progeny trials plot values were adjusted by covariance on neighbouring plots. Standard errors of differences between progenies were usually reduced by 10% and often by over 20% when covariates were formed from the residuals of neighbouring plots and analyses were iterated using successive improved estimates of treatment effects to derive fresh residuals. The method gave larger reductions in error and was effective over a wider range of variates than adjusting on early growth data from interplanted temporary trees of a standard variety.

The effect of Rhizobium strain and low levels of nitrogen on growth and nitrogen fixation was studied on 5 seedlines of Phaseolus vulgaris. All plants responded to irrigation when low levels of nitrogen were supplied throughout each experiment during vegetative growth, but the final seed yield was not significantly affected. All strains induced less nodule tissue and lower nitrogenase activity per plant when nitrogen was applied; some strains were less sensitive than others. The proportion of the plant's nitrogen estimated to be derived from fixation (based on acetylene reduction) and fertilizer was affected by host genetics. Nodulated plants had nitrogenase activities comparable with other grain legumes and responded to combined nitrogen during vegetative growth, but this was not reflected in grain yield.

Seasonal fertilizer response of napier grass (Pennisetum purpureum) was measured on various soils in Brunei. Climate was moderately humid over the three-year experimental period, with the longest dry spell about 4 months. Optimal fertilizer N levels (balanced with other nutrients) ranged from about 240 to 900 kg/ha/yr on the different soil types and under different moisture conditions. Dry forage yields at the optimum fertilizer levels ranged from 5 t/ha/yr on sandy soil under dry conditions, to 55 t/ha/yr on a sandy clay loam with adequate water. Moderate production of about 20 t/ha/yr was obtained on acid sulphate soil with fertilizer and lime. Digestible nutrient and protein levels of 60-day forage were about 55 and 10% respectively.

The yield and gross returns (Rs/ha) were studied over two years in three experiments on intercropping in corn and sorghum. Paired-row planting recorded 8 to 12% and 44% higher yield in corn and sorghum respectively over conventional equidistant planting at the same plant populations. Additional gross returns due to intercropping ranged from 24 to 76% in corn (1975–76 winter) and 4 to 56% in corn and 15 to 75% in sorghum (1976 rainy season) compared to pure crops. Intercropping was beneficial, particularly in the limited cropping periods of this semi-arid tropical zone.