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No abstract

A theory is presented to calculate hydraulic conductivity from successive measurements of water content profiles for soil in situ. With unsaturated soil, potential gradients are inferred using moisture characteristics, but with saturated soil these gradients must be measured directly. The weight of overburden can affect in situ soil water suction, and a method for determining this effect is given. The theory was applied to a soil profile with marked changes in moisture characteristics and texture, and conductivity was determined for several depths as a function of water content.

Theory is presented to permit the calculation of water withdrawal by plant roots at any depth in soil as a function of time, without neglect of water movement in the soil. Such neglect may be a source of error in using other approaches to this problem. The method proposed requires a knowledge of the moisture and hydraulic conductivity characteristics of the soil as a function of depth. When this theory was applied to data from an irrigated cotton crop, it was shown that the maximum rate of water withdrawal by roots was between the soil surface and 25 cm, and that rates were relatively low below 30 cm. The withdrawal pattern is discussed in relation to potential evaporation and the water status of the crop.

Wheat (Triticum aestivum L.) cv. Gamenya was grown in a Mediterranean type environment in two separate field experiments, to determine the effects of nitrogen application and date of seeding on floret survival. One treatment, intermediate in nitrogen level and sowing date, was common in both experiments. Rates and durations of spikelet initiation and durations of the floret initiation period were estimated. At maturity, yield and yield components were measured and occurrence of individual grains at each floret position on odd-numbered spikelets were recorded. The time of floret initiation relative to terminal spikelet formation and the subsequent occurrence of grain were examined.Florets developed first in spikelets 5-13 and last in spikelet 1. Added nitrogen hastened the initiation of florets but did not affect the number initiated; it also increased the numbers of grains per spikelet. In the last sowing date treatment, time to floret initiation decreased, but the sequence of floret initiation was unaffected.Numbers of florets and grains on tillers were less than on main shoots. Only about 28% of all florets initiated developed into grain.The main conclusion was that the florets which initiated before the terminal spikelet formed grain and those that initiated afterwards did not; we accordingly postulate that the vascular system between the rachis and the floret develops as the floret is initiated, but that after terminal spikelet formation, this is inhibited and further grains then fail to develop.