Unpublished, or not easily accessible, details are presented on the establishment of the agrometeorological network in Uganda and the collection, analysis and publication of the observations. Some of the agrometeorological research methods commonly used in Uganda are summarized.

A method is described for constructing a direct-reading scale for leaf area measurement of cereals. The scale is constructed from linear dimensions of leaves, and it enables rapid non-destructive measurements to be made.

A tied ridge system of hand cultivation has been practised successfully in parts of Tanzania for many years. Equipment to mechanize this system was devised and constructed by the National Institute for Agricultural Engineering, U.K., particularly for use in areas of marginal rainfall where water conservation is essential. Agronomic trials with this equipment were carried out on three soil types in Northern Tanzania. Records from resistance units showed much better penetration of rainfall under tied ridges than under flat cultivation. Corresponding yield responses in maize were only obtained when the increase in available water made an appreciable difference to conditions of water stress at the time of tasselling and silking. Weeding operations using a ridging body achieved a satisfactory control. After a few modifications to the equipment, especially the incorporation of a small tine to rip the bottom of the basins to improve infiltration, the system of cultivation based on ripping, ridging and tieing proved to be an adequate alternative to ploughing and harrowing for seed bed preparation, and a much more efficient method of water conservation.

The irrigation water treatments in three experiments were based on a ‘water duty’ principle. One cosec of water was assumed to be available to irrigate 96, 211, 326 or 442 acres, representing minimum irrigation cycle times of 5, 11, 17 and 23 days respectively. Each experiment included a rainfed control treatment. The plots were watered as indicated by a soil moisture profit and loss account, but never more frequently than the minimum cycle time would allow. The results showed that maximum productivity could be achieved on a sand when I cosec of water was used to irrigate approximately 200 acres, but on clay maximum productivity was obtained with the largest water duty (442 ac/cusec). Net photosynthetic efficiency reached 3·9 per cent in the most heavily irrigated crops, and rainfall efficiency fell from about 85 per cent for rainfed conditions to about 50 per cent when the maximum amount of irrigation water was applied.

The concentration of nitrate-nitrogen in cotton petioles was directly related to the rate of nitrogen applied and was greatest at the earliest sampling date, decreasing as the season progressed. There was an increase in the degree of association between the level of nitrogen applied and petiole nitrate-nitrogen, and between petiole nitrate-nitrogen and final yield, up to the time of early flowering, when peak correlation coefficients were reached, after which there was a decline. The level of petiole nitrate-nitrogen showed high positive correlations with the rate of nitrogen application as well as with yield. The final yield showed a significant, positive and linear regression on the level of petiole nitrate at the time of early flowering. A close relationship was also shown to exist between a critical concentration, represented by a narrow range of nitrogen levels in the neighbourhood of 2000 parts per million, and final cotton yield. Yield reductions were related to the number of days petiole nitrogen remained below the critical concentration. The use of petiole analysis as a guide in the nitrogen nutrition of cotton, in the evaluation of various experimental treatments and as an aid in interpreting research results, was demonstrated.

The single-liquid infiltration method of measuring stomatal opening was adapted as a practical field method for determining the time of irrigation of cotton. A number of different liquids, leaf positions and times of measurement were tested and the most sensitive method was selected on the basis of the results. No stomatal response was found while soil moisture was depleted to one-third of available water. A steep reduction in stomatal opening was observed with further drying of the soil. Some results are presented from an irrigation experiment where irrigation control by infiltration method was compared with other methods. The practical possibilities in the use of the method in field practice are discussed.

To investigate seasonal effects on nodulation of legumes during an English summer, plants of Pisum sativum and Phaseolus vulgaris were sown in pots in the open at intervals of 14 days between March and July and the pots were watered on all days when rain did not fall. The weight of nodules per plant varied significantly between sowing dates and showed seasonal trends in both legumes, but in different directions. In P. sativum nodulation was at a minimum at the midsummer sowing date but with P. vulgaris the mid-summer sowing gave maximum nodulation. The data are further analysed in terms of number and size of nodules, and nodule weight as a percentage of plant weight.

An experiment was conducted in 1964 and 1965 to study the effects of hormone sprays on pod setting, pod filling and grain yield of black gram. Sprays of 2-naphthoxyacetic acid and p-chlorophenoxyacetic acid, alone and in 'mixture, and gibberellic acid and 1-naphthaleneacetic acid increased pod setting, but grain filling in pods and grain size were only slightly improved. 2-naphthoxyacetic acid gave the highest yield, followed by p-chlorophenoxyacetic acid, 1-naphthaleneacetic acid and a mixture of the first two, which increased yield by 56, 39, 36 and 35 per cent respectively over the control and gave economic returns.

The percentage dry matter of some Nigerian vegetables increases with age. Corchorus olibrius gave the highest yield of vitamin C after five weeks, but the stage of maturity had less effect with other vegetables. The oxalic acid content of Celosea argentea was very high, approaching a lethal level. It appears that some of the vegetables are best at about six weeks from sowing from the standpoint of eating quality, oxalic acid and vitamin C content.

The problems involved in the estimation of potential evaporation in the tropics are discussed, and available methods for calculating potential evaporation are assessed. A computer programme is described which evaluates Penman's formula, accommodating data from the very wide range of conditions experienced in tropical agriculture. The programme conforms with recent W.M.O. recommendations and is written for computers available in many parts of the world. An important component of the programme is a strict data validation procedure. The output includes daily and mean ten-day estimates of E, using the reflection coefficients for open water and for a crop as well as both calculated and, where available, measured values of radiation.