Incorporation of dry matter of perennial soybean into the soil, alone or with mineral fertilization, resulted in improved vegetative growth of common beans. Fairly high LAI was observed at flowering time where dry organic matter had been added, causing leaf self-shading and decreased growth in the later states of development. In contrast, both the control and mineral fertilized plots showed slower but continuous growth up to 50 days from plant emergence. Only slight differences in grain yield were noticed despite remarkable increases of Crop Growth Rate, Relative Growth Rate, Net Assimilation Rate, and Efficiency of Solar Energy Conversion that resulted from the application of dry organic matter.

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.

Data of uniformity trials on apple in farmers' gardens showed large localized and genetic variation, indicating that larger plots could be used with advantage. Formation of blocks on the basis of uniformity trials can be expected to increase block efficiency considerably. With only four to six years for experiments it was found better to use trunk girth as a calibrating variate for forming plots and blocks instead of losing two years for a uniformity trial. The minimum number of replications needed to obtain estimates of treatment effects with a given standard error has been calculated. There was a pronounced biennial swing in the yields as reflected by the intra-tree correlation.

Yields in a trial of Upper Amazon clones, derived from high yielding Upper Amazon selections, were low in the early years. One Upper Amazon clone was significantly higher yielding than any other clone, but generally yields from the Upper Amazons were comparable to those of Local Trinitario selections included as controls. The Upper Amazon clones were highly variable in establishment, yield and losses from diseases. The relationship between the performance of some of the clones and their parent seedlings is discussed.

Nitrogen was lost through leaching, both as and , even after application of the ammoniacal form in a reduced soil zone. Under saturation the loss was more through , and under submergence through nitrogen. The loss was accelerated when all the nitrogen was applied at one time at the early stage of crop growth. Application at transplanting proved unproductive. Three split application at active vegetative, reproductive and ripening phases helped to give maximum responses in both alluvial clay and lateritic sandy clay loam soil.

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 analysis is presented of a 17 variety maize diallel cross grown in Tanzania at 1300, 500 and 200 m. Thirteen of the varieties included Central American material, mainly Caribbean and Flint types, and four were derived from Eastern African Flat-White maizes. Variety cross performance was much affected by environmental conditions. At 200 and 1300 m., four of the top five varieties were the same, and selection of varieties for composite formation was not particularly critcal. At the 500 m. site, order of yields differed markedly from the other sites, and predicted composite yield was much more affected by the choice of varieties included. Criteria are discussed for selection of varieties to be included in composites at the three altitudes.

Thirty one soils from the Savanna Zone of Nigeria were low in exchangeable potassium, ΔK°, and ΔK°° and had very low potassium buffer capacities. The soils were low in clay, which was kaolinitic. Two soils high in 2:1 layer clay minerals contained higher quantities of labile potassium. Total potassium varied with parent material. Release of non-exchangeable potassium was low. After cropping, wet/dry cycles released exchangeable potassium. Potassium deficiency is expected to occur commonly with intensive cropping in the field.

In upland rice, seed soaked in CCC for 24 hours before sowing or sprayed with CCC 10, 21, 42 and 63 days after sowing, showed severe lodging. Effects of CCC on the number of paniclebearing tillers, number of good grains in 1000 grains, weight of 100 good grains and grain yield were not significant. On the other hand CCC prevented lodging in swamp rice, with the lowest percentage when foliar spray was given 21 days after transplanting. CCC failed to increase the number of panicle-bearing tillers and grain yield in swamp rice.

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.

The effect of covers of controlled volunteer vegetation, Pueraria phaseoloides, and clean weeding on the soil moisture content and on the succulence of sisal leaves was studied. The surface soil tended to dry out further when exposed by clean weeding, but moisture in the profile as a whole was not much depleted. The plant covers dried soils to at least 300 cm. in dry periods. Although sisal leaves had a slightly higher dry matter content in dry weather there was no evidence of competition for water between the plant covers and the sisal.

Soil properties influencing N mineralization, and hence the potential N-supplying power of 154 West Indian soils, have been studied. Mineralizable N was correlated with the activity of the soil biomass measured as extractable glucose, with exchangeable bases in base-deficient soils and with total N in soils well supplied with bases, but not with other estimates of the nature of soil organic matter (e.g. extractable chlorophyll or C : N ratio). It is suggested that cation exchange capacity and percentage base saturation may influence the N-supplying power of West Indian soils more than their total N content.

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.

Water use by maize at three densities was measured by a complete water balance, including soil moisture, rain, applied irrigation and deep drainage in crops irrigated so that relative turgidity at noon remained above 90 per cent (i.e. no-stress conditions). Total evapotranspiration between planting and harvest, 56 cm., was not significantly affected by density, but evapotranspiration was slightly higher at higher densities when ground cover was less than 50 per cent. Actual evapotranspiration rose to 1 cm. per day during anthesis and grain filling. A fifth of the water applied moved beyond the root zone, indicating that work on more permeable soils would be inaccurate if the deep drainage component was ignored.

Young tea plants were grown for eight months in large polythene bags of soil, with provision to prevent rain from running into the soil. After a preliminary period of establishment, in which all plants were kept well-watered, four soil moisture regimes were applied ranging from watering twice weekly to withholding irrigation until plants had been subjected to a soil moisture tension of 15 bar, as determined by gypsum resistance units, for a period of one week before rewatering. Plant survival and growth were significantly better under the wettest compared with the driest regime.

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.

A method is described for studying the distribution of absorbing roots of fruit trees using the number of light root tips per unit of soil space as a criterion for characterizing the spatial distribution of the absorbing parts of the root systems. As examples of the use of this method, some results are shown from investigations with apple trees in South-Western Germany. They demonstrate the influence of soil-type and soil management on the distribution of absorbing roots. Striking temporal variations in the number of root tips were observed in the same tree.