SUMMARYAn experiment was conducted during the 1978/79 summer at the Central Cotton Research Institute, Multan-Pakistan to evaluate the crop production patterns of two cultivars of cotton (G. hirsutum L.) differing in their reaction to heat-induced sterility. Boll set in variety ST3 amounted to 7.7% of the total fruiting points, from flowers opening during the hottest months of June, July and early August, while almost all the fruiting points produced by cultivar B557 during the same period were shed and no bolls were set. Of the flowers examined during July, 83.3% in B557 contained non-dehiscent anthers against 6.7% in ST3.

Key words Buffering capacity EUF extracted phosphorus Readily available phosphorusReserve phosphorus Seed cotton yield Slowly available phosphorus Summary Preliminary investigations were carried out on calcareous silty loam (clay content 25%, pH 8.0) at the Cotton Research Institute, Multan to determine the solubility and desorption rates of phosphorus at various soil depths throughout the cotton growing season using the EUF technique.The treatments included two applications of single superphosphate, equivalent to 0, 75, 150, 250 and 350 kg P2Ojha. There was no significant difference in seed cotton yield between the five treatments. EUF-extracted phosphorus decreased with depth in all samples. There was an increase in phosphorus concentration during the growing season, but most of the increase was noted in the slowly available phosphorus fraction (10-30 minutes EUF aliquots). This was attributed to continuous transformation of phosphorus into less soluble calcium phosphate forms. The available phosphorus fraction (0-10 minute EUF aliquots) remained small throughout the growing season. It was concluded that this fraction was in equilibrium with the slowly available phosphorus fraction and was continually being replenished as crop uptake continued. A high level of effectively available phosphorus (0-30 minute EUF aliquots) was recovered in all five treatments and was above the sufficiency level of 12 ppm phosphorus reported by Nemeth and Makhdam 7. There was therefore no difference between treatments in phosporus concentration nor in phosphorus uptake by plants.

The consumptive use of water by cotton (G. hirsutum L.) variety 149F, sown at three dates, was calculated using Penman Et x crop factor method. The earlier the sowing date the more water evapotranspired, mainly due to differences in the length of the growing season and the amount by which it coincided with the monsoonal depression of potential evapotranspiration. An example is given of calculating the irrigation requirements of a mid-June sown cotton, accounting for average rainfall, showing that the water requirements of cotton during the early stages may be adequately met by the establishment irrigation and rains during July. Examples are cited to show that a charged profile at the beginning of the season may sustain good growth and produce satisfactory yield.The actual water use by crops varies greatly between seasons and locations, depending mainly on the evaporative condition of the atmosphere and the crop characteristics that determine ground cover and roughness of the canopy. Several direct and indirect methods for determining crop water requirements are reported in the literature (Israelson and Hansen, 1962;Hudson, 1965;Chang, 1968). The indirect methods include the use of different evaporation pans and empirical formulae to estimate evaporation from an open water surface, or potential evapotranspiration from a reference crop. These estimates are then related to actual water use by various constants, in a general relation represented by:where ET= Actual evapotranspiration or consumptive use, E = Potential evapotranspiration (evaporation from a short green crop, actively growing, completely covering the ground and adequately supplied with water), E o = Evaporation from an open water surface, and K = Crop or pan factor.The Penman method (Penman, 1948) which estimates E o , and its modification (Penman, 1956), which estimates E t , are widely used to calculate crop water requirements in both temperate and tropical climates (Chang, 1968;Farbrother, 1970). The Penman formula, combining a radiation energy term and an aerodynamic component, requires the following meteorological data; t This work has been carried out under UNDP/FAO Project PAK/73/026.

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