The effects of nitrogen fertilization on growth, nutrient uptake and yields of upland and lowland taro were studied on the island of Kauai, applying o, 280, 560 and 1120 kg./ha. N. Nitrogen concentrations of upland and lowland taro leaves were significantly correlated with yields, although regression analysis showed that per cent N in both blades and petioles decreased with age. Higher yields were obtained from the lowland than from the upland crop, regardless of amounts of N fertilizer applied. The highest yield obtained from lowland taro was at 1120 kg./ha. N harvested at fifteen months (57·6 tons/ha.) and from upland taro the highest yield was obtained at 560 kg./ha. N harvested also at fifteen months (25·5 tons/ha.).

The yield data obtained from fertilizer experiments conducted at 195 locations for three years were examined to study the relations between yield, response to nitrogen and phosphorus, soil test values, and number of irrigations, using multiple regression technique. Irrigation accounted for 20–36 per cent of the yield variation, whereas soil factors did not show appreciable effects. Nitrogen response was influenced by irrigation, while some soil factors affected response to phosphorus.

The growth of improved short varieties of rice with low and high tillering capacities was compared under a wide range of nitrogen levels and spacings. A high tillering variety performed better than a low tillering one under the experimental conditions tested. Leaf area index values as high as 10 to 12 were not detrimental to grain production unless the crop lodged.

Under controlled environment conditions rice variety IR8 was subjected to night temperatures of 15, 20 and 25°C during each of the three periods (a) sowing to floral initiation, (b) initiation to panicle emergence, and (c) panicle emergence to maturity, with day temperatures of 30°C throughout. Night temperatures of 15°C prevented floral initiation throughout the experiment, an effect partly overcome by transfer to higher temperatures after 102 days but not without yield loss. The optimum night temperature was 20–25°C, with some evidence of change of temperature effects, as distinct from the effect of actual temperature levels. As IR8 was developed under relatively stress-free conditions, its sensitivity to temperatures below 15°C may be greater than in varieties developed elsewhere.

Eight trials, covering a wide range of conditions in Malawi, have assessed the effect of applying nitrogen (0, 45 and 90 kg. ha.−1), sulphur (0, 22, 45 kg. ha.−1), phosphorus (0, 15 kg. ha.−1) and boron (0, 0·63 kg. ha.−1) on growth and yield of cotton. A nitrogen × sulphur interaction was very highly significant at one site, and good responses to nitrogen were obtained at six sites. Phosphorus and boron gave significant increases at one site. Increased yields of seed cotton indicated that there is an overall need for a compound fertilizer to supply nitrogen, sulphur, boron and in some areas phosphorus.

Established plants of bermudagrass (Cynodon dactylon (L.) Pers.), johnsongrass (Sorghum halepense (L.) Pers.) and purple nutsedge (Cyperus rotundus L.), grown in containers, were repeatedly clipped to the ground from spring to winter, at monthly and bi-weekly intervals. Regrowth of bermudagrass was markedly reduced after monthly clippings, but all plants regrew in the following March; there was no regeneration in March of bi-weekly clipped plants. Severe decrease of regrowth of clipped johnsongrass occurred after bi-weekly or monthly clippings, but a quarter of the clipped plants regenerated in the following March. Nutsedge was more resistant to clipping than the other two species and all clipped plants regrew vigorously in the following March. Repeated clipping reduced the rhizome length or tuber number and the dry matter content in the regrown plants in proportion to the frequency of clipping.

Ten wheat crosses between tall local varieties C228 and C591, a short local variety C271, and short Mexican varieties Penjamo, Nainari 60, Pitic 62 and Sonora 64, were field-tested under irrigation for heterosis for plant height, grain yield, spikes per plant and kernels per spike. Heterosis occurred to a greater degree for the last three attributes in some of the crosses, with the greatest heterotic expression in crosses involving Penjamo and Pitic 62 and the local variety C591.

A pot experiment was carried out to study various aspects of growing peanuts in highly calcareous soil, with special reference to iron chlorosis. There was good agreement among the criteria used to evaluate the need for iron and the effectiveness of different chelates or methods of application (i.e. visual symptoms, chemical diagnosis and yield response). Of the iron chelates tested, Sequestrene 138 proved the most effective. Promising results were also obtained by coating seeds with chelate as an iron starter, followed by an additional top dressing. The results indicate the possibility of growing peanut economically in the highly calcareous soil tested using iron chelate —Fe EDDHA (Sequestrene 138).

Weekly measurements in a maize silage crop grown at three populations, each at three levels of nitrogen, showed that leaf area index, crop growth rate and total whole plant yield were greatest at the highest plant population (430,000/ha.) and lowest at the low population (47,000/ha.). At the former maximum yields of dry matter and crude protein occurred approximately seventy-five days from sowing, when the cob contribution was small. With wider spacing maximum yields occurred later. At the intermediate population (107,000/ha.), and with adequate nitrogen, sowing on the square was superior to sowing in wide rows. Nitrogen did not preferentially affect the relative dry matter yield of any growth component; plant population had a greater influence on total whole plant yield than nitrogen.

The effect of fungicides on the development of powdery mildews on cucumber and okra was studied. Most of the chemicals tested controlled the disease and significantly increased yields, though a dimethirimol-resistant Oidium sp. appeared on okra. Seed dressing with the systemic fungicides thiophanate and benomyl conferred resistance to the disease for a few days whereas soil application gave protection for more than eleven weeks.

The concentrations of total nitrogen and nitrate–nitrogen in yam leaves receiving various levels of nitrogen were determined fortnightly. Nitrate–nitrogen was superior to total nitrogen as an index of nitrogen nutrition. Correlation coefficients between nitrate–nitrogen at various sampling dates and rate of nitrogen application were highest between late June and early July in two seasons, indicating that this is the best time to take single samples for foliar analysis. A relation was demonstrated between nitrate–nitrogen at this period and tuber yield.