Instruments and techniques are reviewed for measuring the content and potential of water in the soil, the water potential and solute potential of plant tissue, and the diffusive resistance of leaves. Emphasis is placed on difficulties encountered in the field and in the interpretation of measurements. References are given to recent technical papers and reviews dealing with the principles and construction of individual instruments.

When agricultural experimenters send data to a statistics unit for analysis, they do not usually include a field plan of the experimental site unless specially requested to do so. But such a plan can be a great help to a biometrician: he can use it to check that the design used in the field was correctly described, and to arrange the plot residuals in the field layout as a way of detecting a fertility trend in the site and of relating anomalous values to particular locations on the ground. This paper gives examples of how a field plan can be used to the benefit of the experimenter.

A field technique is described in which trenches were dug and vertical polythene partitions installed to eliminate below-ground interactions between component crops in intercropping. With pearl millet/groundnut the control intercrop (i.e. not dug out) gave a yield advantage of 22% compared with sole cropping. A treatment dug out but refilled without polythene partitions was very similar to the control intercrop, indicating that the digging procedure per se had little effect on growth. An intercrop treatment in which below-ground partitions were installed gave a yield advantage of 19% over sole cropping, suggesting that the main determinant of yield advantage was an above-ground interaction between the canopies. However, partitioning decreased millet yield and increased groundnut yield, indicating that below-ground interactions were important in determining the competitive balance of the two crops. It is concluded that the partitioning technique is promising.

A technique is described that allows neutron meter access tubes to be reinstated in tilled soil without disturbance below the depth of ploughing or tine cultivation. In a test there was no evidence of greater water movement to depth around reinstated access tubes compared with newly inserted ones.

Nitrogen fertilizer requirements and potential forage yield of wheat, oats and Italian ryegrass grown under irrigation in Saudi Arabia were assessed. Mexipak wheat produced high DM yields with between 100 and 150 kg/ha N, and the mode of nitrogen application did not significantly affect DM outputs. Nitrogen at 150 kg/ha produced highest DM yields for oats, although the application of 50% of irrigation requirement as drainage water reduced yield by 8%. Italian ryegrass produced a mean yield of 14.6 t/ha in 169 days with a nitrogen application of 60 kg/ha; direct drilled on a field scale it yielded 8.76 t/DM/ha with a total application of 270 kg N/ha.

Nitrogen fertilizer requirements and potential forage yield of maize and two millet types grown under irrigation in Saudi Arabia were assessed. Nitrogen application at 50 kg/ha produced mean yields of up to 15.7 t/ha in maize variety Pioneer H.3147. Splitting the nitrogen application did not significantly affect yield. Nitrogen above 100 kg/ha did not significantly increase DM yield of Proso millet (Panicum miliaceum). Mean total DM yields of 17.6 t/ha of Setaria italica were produced, after 111 days, with 150–200 kg/ha of nitrogen; 150 kg/ha of P2O5 produced a mean DM yield 7.9% higher than 75 kg P2O5/ha.

The response of Italian ryegrass (IRG) to nitrogen fertilization, irrigation frequency and harvest interval indicated that management of nitrogen and water is the determinant of productivity under semi-arid northern Mexican conditions. Where water is non-limiting the effects of harvest interval can be eliminated. A soil moisture balance model indicated the inadvisability of seeding IRG in sandy soils if water is a scarce resource because of the high frequency of irrigation that would be required. The seeding (September) and late production (April) periods were identified as critical in regard to irrigation need and limiting in terms of the area that it would be possible to seed.

Puncture tapping and one-eighth spiral (S/8) tapping, both combined with Ethrel stimulation, were compared with conventional half spiral (S/2) tapping of immature Hevea trees. Stimulated puncture-tapped trees in some experiments yielded more rubber and had much more sucrose in the latex than unstimulated half-spiral tapped trees. Yields of puncture-tapped trees also increased with increase in the quantity of Ethrel and the number of punctures, but were not affected by the size of puncture. Girth increments of the trees and percentage dry rubber content of the latex were approximately equivalent in all three methods of tapping.

Field experiments were conducted for 3 years covering 4 crop seasons at Lucknow to study the utility of pigeonpea (Cajanus cajan) as an intercrop in economizing N for maize (Zea mays) and to assess the residual fertility of kharif crops on autumn-planted sugarcane (Saccharum officinarum). Pigeonpea increased the soil N content due to substantial nodulation, but as an intercrop it did not increase the yield of maize at any level of nitrogen. Sugarcane grown after pigeonpea yielded 43% more than when grown after maize. Intercropping pigeonpea in maize would be more beneficial than growing a pure crop of maize before planting sugarcane.

Gibberellic acid (GA) at 1500 ppm, applied as foliar spray or pre-plant soak, effectively promoted flowering in Nigerian clones of the cocoyams Xanthosoma and Colocasia. A foliar spray (technical grade GA) applied with 0.25% surfactant gave better results than with 0.01% surfactant or than a foliar spray of Pro-Gibb Plus (commercial GA formulation). A pre-plant soak of Pro-Gibb Plus was least effective but could be useful in poorly equipped research stations.

Changes in growth rate of tea shoots cause yield fluctuations between seasons, but the size of the basal shoot population remains constant throughout the year. The proportion of shoots with dormant apical buds does not influence the mean weight of shoots harvested. Models of shoot extension are discussed.

An experiment on wheat (variety Mexipak) was undertaken for two years at the Experimental Farm to study the effects of soil and foliar application of urea. The results indicated appreciable increases in grain yields due to foliar sprays of urea during both years of the experiment; the spray helped to increase yield-contributing factors such as thousand-grain weight, weight of grains per plant, plant height and dry weight.

Changing the geometry of planting under irrigated conditions from the traditional pattern of regular rows (with plants equidistant from each other) into double rows (with plants arranged in row pairs) promoted plant competition. This resulted in a significant reduction in overall yield components of sorghum but a marked increase in shoot yields of striga. A better yield of sorghum was obtained in ridged plots than in flat plots, associated with less striga infestation and a slightly higher soil moisture content under the ridged plots.