Application of zinc to six high-yielding rice varieties in calcareous soils produced significantly higher grain yield and interactions between varieties and Zn levels were significant. Yields of varieties IR 20, Jaya, Sita and Jayanti at 2.5 and 5.0 ppm Zn were similarly affected, but Archana produced significantly higher grain yield at 5 ppm Zn than at 2.5 ppm. Effects of Zn on straw yield were similar. Zn application invariably resulted in a higher Zn concentration in plants at all stages of growth and in grain in all varieties. Maximum Zn contents were observed at the tillering stage and minimum at harvest.

The yield potential of a highly productive non-commercial Type IV bean cultivar was determined under optimum field conditions, grown in monoculture at 1 plant/m2 on trellises 3 m high. Canopy growth was analysed by dividing the stand into 25 cm horizontal strata. The main components of yield were number of inflorescences and number of pods per stratum. Daily yield for the growing period was 4.9 g dry weight/m2. Although a high yield per plant was recorded (823 g/plant) drop of young pods and seed abortion were the major factors reducing the potential yield.

Fourteen smallholder coconut plantations, subdivided into 27 uniform sub-units, were surveyed in an area around Dala, in Western Malaita, Solomon Islands. Most units (17 out of 27) had densities of 160–200 palms ha−1 with a median light transmission of 50–55%. Palm growth was poor due to low soil K, and copra yields averaged only 540 kg ha−1 year−1 Batiki (Ischaemum aristatum) was the most important sown grass, and its productivity was significantly related to stocking rate and weed control, but not directly with light transmission. Farmers should thin dense palm stands, adjust stocking rates in relation to actual areas of pasture available, and institute careful and adequate weed control.

Significant differences were found between 20 chickpea cultivars and four locations in respect of the concentration of protein in the seeds. Cultivar x location interactions were also significant. The average protein concentration among cultivars varied from 18.5 to 23.2% and among locations from 18.3 to 22.7%. Correlations between seed protein concentration and seed yield and seed size were very small. Protein concentration was influenced by available nitrogen in the soil.

The effects of three irrigation intervals (7, 10 and 15 days), four nitrogen levels (0N, 1N, 2N and 3N where 1N = 43.8 kg N/ha), and 0 or 11.9 tons/ha gypsum on leaf N, P and K uptake by forage sorghum grown on a highly saline–sodic clay soil were investigated in two successive seasons. The two seasons' data consistently showed that both leaf-N and leaf-K increased significantly with increasing N-rate and by splitting the same quantity of irrigation water into more frequent irrigations. Gypsum had no consistent effect. The responses of both leaf-N and leaf-K to nitrogen rates were significantly linear and a linear response of dry matter yield to leaf-N was also observed. P uptake was improved by more frequent irrigations in the first cutting of 1978, but was not otherwise affected by treatments.

In maximizing productivity levels in oilseed sesame (Sesamum indicum) one of the major constraints is the large-scale shedding of buds, flowers and capsules. The present study examines the reproductive behaviour of five sesame genotypes with a view to ascertaining the extent of production, shedding and retention of different reproductive organs. Sesame genotypes produce 250–350 flower buds per plant but shed most of them at different stages of development. Shedding is thus excessive, and 86–91% of the reproductive potential was not realized in this study, thus limiting yield. Improvement in yield through increased fruit retention is essential.

The response of tea shoots to temperature was studied in the field and in controlled environments. Shoot extension stopped below about 12.5°C. Shoots of mature tea took 491 day degrees above the base temperature of 12.8°C to grow to a harvestable size of 15 cm.

A field experiment was conducted for two consecutive years commencing in 1979–80 on the Indo-Gangetic alluvial soil of Pura to investigate the requirements for zinc of wheat, chickpea, mustard and Egyptian clover. Chickpea and Egyptian clover were more sensitive to zinc deficiency than wheat and mustard, respectively. Average total dry matter production by Egyptian clover and wheat was larger than mustard and chickpea. Egyptian clover and wheat required more zinc to achieve maximum dry matter production but they also recovered from the soil a larger proportion of applied zinc than chickpea and mustard. Mustard produced the most dry matter per unit of zinc absorbed.

Temperature is the major environmental variable affecting the yield of tea, but within the framework of a temperature model shoot extension is severely depressed when daily maximum vapour pressure deficits rise above 2.3 kPa. Day length does not affect shoot extension when the nights are cool (10°C), but growth rate is depressed by short days (11 h) when nights are warm (20°C). Soil temperatures between 18–25°C do not affect shoot extension.

COCA (highland), TZPB (lowland) and COCA x TZPB maize varieties were tested at Bambui Plain (1330 m) and Ekona (550 m). Leaf blight and rust were controlled chemically with Dithane-M45 and Benlate, and their use significantly increased the yields of COCA when grown in lowland environments, where it does not possess resistance to lowland leaf blight (H. maydis) and rust (P. polysora); yields of TZPB were similarly increased in highland areas, where it is susceptible to highland leaf blight (H. turcicum) and rust (P. sorghi). COCA x TZPB was intermediate in resistance to both diseases at the two locations.

The relation between source potentials and sink capacities of four cassava (Manihot esculenta Crantz) varieties with different characteristics was investigated by means of reciprocal grafts. There were marked differences in the sink capacities (average stock effects) and source potentials (average scion effects) of the varieties.

A continuous non-limiting soil water supply, or a non-limiting supply from 120 to 180 days after planting, significantly increased (P = 0.01) female flower production of banana cv Robusta compared with continuous soil water stress. Relieving stress after 120 days produced a significantly higher (P = 0.05) average number of female flowers per inflorescence than when adequate water was supplied throughout. Female flower production is positively correlated with the average growth rates at floral initiation and early floral differentiation and with the final pseudostem girth.

Diurnal variations in soil temperature were measured under tea plants with different kinds of mulches. During the early years after planting temperatures differed, depending on the type of mulch and its heat absorptivity. Black plastic and stone chippings showed the greatest diurnal variations, but the variations disappeared in all treatments when there was a ≥ 60% canopy. Tea plants themselves modify soil temperatures, which could affect growth and yield in places where soil temperatures are generally lower.

The effects of soil fertilization and plant age on the nutrient composition of various parts of five Nigerian cassava varieties were studied to identify suitable index plant tissue(s), sensitive growth stage(s) and optimum nutrient concentrations, to develop better fertilizer practices for the crop. The third month from planting was the most sensitive stage for diagnostic sampling, when N status was best reflected in leaf blades and K in petioles. N and P were most concentrated in leaf blades and least in root tubers. The largest root tuber yields after 12 months were associated with leaf blade analyses of 5% N, 0.4% P and 2% K at 3 months after planting.

In two field experiments, sweet potato showed symptoms of lime deficiency, and consequently produced extremely low DM, at the natural pH of local peat (3.5–3.7). Liming to increase pH remarkably increased tuber and vine dry matter to pH 5.5 and harvest index to pH 3.8, but higher pH values decreased dry matter and harvest index. Tuber and vine yields generally decreased with continuous monocropping, probably because of increasing infestation with weevils (Cylas formicarius) and other pests, and depletion of available nutrients.

Papaver bracteatum Lindl., a potential source for codeine production, is a perennial species which is known to flower from the second year of growth. Through selection and early planting date, a high flowering rate (96%) was achieved during the first growing season. The flowering response and yield of capsules were very sensitive to planting date and seedling type. Delaying planting markedly decreased both flowering rate and yield of capsules in the first year. Direct sowing was more advantageous than transplanting. A yield of 36 g/m2 of dry de-seeded capsules was obtained during the first growing season by direct sowing in late summer.

Different subspecies of Arachis hypogaea show variation in their ability to nodulate in the hypocotyl region. Some cultivars belonging to subspecies hypogaea nodulate profusely on the hypocotyl, while those of fastigiata nodulate rarely in this region. The utilization of this character in breeding for increased nitrogen fixation is discussed.

Time of planting was found to significantly influence insect damage, quality of harvest and yield of cowpea in southern Nigeria. The greatest insect damage occurred on the August planting. Maruca testulalis was the most serious pest on cowpea whilst thrips were the least. Dry grain yield was higher in the early season plantings but quality of harvested crop was better in the late season plantings. These observations were also influenced by cultivar differences.

Two field experiments studied the nitrogen fertilizer requirements of guinea and napier grass on peat. Plants in the control plots, though optimally limed and fertilized with other nutrients, absorbed only 1.7 and 2.4% of total peat N in a year and N fertilization improved DM yield, with an optimum at 900 kg/ha/yr. Further positive response was not observed, probably because of a reduced ratio of N to other nutrients. Optimum N uptake, and N concentration in the DM, were achieved at 600 kg/ha/yr N but N recovery decreased linearly with increasing fertilizer N at the rate of about 2–4% per 100 kg/ha/yr N.