Trials were carried out to ascertain which of four systemic insecticide/nematicides were absorbed by young coconut palms (Cocos nucifera L.) using three different methods of application. Stem injection of Bidrin and Nemacur are impractical because the chemicals break down too quickly and frequent retreatment would result in too much physical damage to the young trees. Lannate was not absorbed from leaf axil placement, and broke down too quickly when absorbed from the soil to be of practical use. Nemacur was not absorbed through the leaf axil, but was from the soil and lasted up to 14 weeks in the plant. Temik, absorbed both through the leaf axil and from the soil, lasted up to 14 weeks. The possibility of controlling red ring disease of coconuts with Nemacur or Temik is considered.

Root and sugar yield responses of the Polyrave variety were more favourable to the lower of two population levels (70,000 and 92,000 beets/ha.) and to the wider of two between-row distances (60 and 50 cm.). When the triploid Trirave variety was space planted and, for comparison, conventionally planted and thinned to 3 population levels at 60 cm. between-row distance, the intermediate (87,000 beets/ha.) level gave the highest sugar yield. The thinned treatments consistently outyielded the corresponding space-planted treatments. Space planting at 40 cm. between-row distance resulted in high beet populations (130,000 beets/ha.) which evoked unfavourable responses in root and sugar yield and even in sugar content.

The shallot is a common crop in tropical areas where daylength and temperature conditions do not permit the growing of onions. Shallots are dormant for 70 days from the time of harvest to sprouting in bulbs stored at room temperature (75 to 95°F), during which period about 40 per cent of the bulbs are lost due to drying out and disease. Bulbs stored at lower temperatures (40 to 60°F) sprout more rapidly, with an optimum of about 50°F. Cool storage enables the farmer to use the previous season's crop for planting within 30 days of harvest.

Linear regression of grain and straw yield of dwarf wheats on level of fertilizer nitrogen was significant, but the efficiency of fertilizer nitrogen was determined by the time and method of its application. A single application as a basal dressing was the least productive for grain yield, while split fertilization at sowing and at first irrigation increased the efficiency of applied nitrogen. Further splitting in three doses did not benefit wheat. Foliar application of nitrogen to replace top dressing at the heading stage was of no advantage while replacement of a top dressing at first irrigation by urea spray at heading was definitely deleterious.

The variation in number and yield of tubers from three commercial fields of sweet potato was measured over three seasons. Sources of variation were attributed to factors external to the plant, such as soil, management and climatic differences, and to inherent plant factors, including type of planting material. It is suggested that a reduction in variability could lead to increases in productivity, and may also increase the precision of field experimentation.

Under controlled environment conditions a semi-dwarf wheat, Mexico 120, was subjected to day temperatures of 32 and 27°C, with night temperatures of 21 or 16°C, which are similar to those occurring for a large part of the dry (winter) season of the Ord River valley area of northern Australia. Temperature differences imposed only during the 23 days between sowing and floral initiation produced effects which persisted throughout later growth, when all plants were grown under one temperature regime. The effects of temperature differences before floral initiation were greater than those of similar temperature differences imposed after ear emergence began. The maximum temperatures occurring even in the coolest months probably limit maximum potential grain yields in an environment similar to that of the Ord River valley.

Under controlled environment conditions a semi-dwarf wheat, Mexico 120, was subjected to temperature regimes representative of the extremes that occur during the dry (winter) season of the Ord River valley in northern Australia. High temperatures (35°C by day: 18°C by night) such as occur at the beginning and end of the dry season were compared with low temperatures (30°C by day: 13°C by night) such as occur in mid-season. Day length was constant at 12 hours. High temperatures from floral initiation onwards adversely affected floret development, and after ear emergence reduced grain filling to nil. Net assimilation rates were reduced by high temperatures. Major effects on yields were caused by high temperatures well before anthesis. The critical temperature after anthesis is apparently between 32° and 35°C.

The stomatal functioning of high, medium and low yielding clones of tapioca was examined to see whether yield could be associated with conductivity and/or resistance to moisture stress. A sensitive falling pressure porometer was used to measure stomatal conductivity to the viscous flow of air at small pressure differences. No marked differences were observed which could account for the large range in yields shown by the varieties, but stomatal functioning could be related to canopy type and to planting conditions. In general the conductivity values of all three varieties were very low compared to many other crop species, which suggests that increases in canopy efficiency and yield could be obtained in certain environments by an increase in leaf conductivity.

Whole branches were removed from trees in the field, at regular intervals, to follow the increase in dry weight of fruits and new vegetative growth. Information on the partition of carbohydrates was gained by comparing the growth of untreated, defoliated, de-blossomed and ring-barked branches. Untreated branches increased in weight rapidly when their fruits began to expand, probably because they imported carbohydrates, and their net photosynthetic capacity increased. More young fruits were shed from defoliated than from untreated branches, thus partially compensating for loss of leaf. Non-fruiting, and sometimes fruiting, branches exported a considerable amount of assimilate during the dry seasons, when the trunk-root system was a relatively important dry matter sink. When there were many fruitless branches on fruiting trees, the fruiting branches imported carbohydrates from them during the whole period of fruit growth, whereas fruitless branches imported carbohydrates only when there was a ‘flush’ of shoot growth.

In tropical legume-grass swards random core sampling recovered too few nodules to be a useful method. Core sampling of individual plants with a 5·0 cm. Stace tube showed similar changes in nodulation as total root excavation. However, the nodule distribution was different on the root systems of the two species studied, Desmodium uncinatum and Phaseolus atropurpureus. Nodule weights per plant on these species were much higher than any previously recorded in the literature. The direct contribution from nodule decay to the total end-of-season nitrogen release was estimated and shown to be small, approximately 14 per cent for D. uncinatum and 8 per cent for P. atropurpureus.

In experiments with transplanted rice, the first row next to the unplanted alley consistently gave significantly higher grain yields than the centre rows. The increase was progressively higher as the width of the unplanted alley between plots was increased up to 100 cm., but where the increase was very large, yields of the second outermost row were significantly decreased. No evidence was found that border effects reach beyond the second outermost row. Varieties that differed in tillering capacity, plant height, or both responded differently to the unplanted borders.