The productivity of seven multiple rice-cropping systems, utilizing a short-duration cultivar under irrigation, were assessed over 5 years. Systems of one, two and three crops a year were compared. Multiple cropping reduced grain yield, panicles m-2, total dry matter and nitrogen uptake per crop. However, the unfertilized three-crop-per-year system averaged 9·1 t grain, 17·1 t DM and 126 kg N ha-1 per annum, without showing a long term decline in productivity. Recovery and utilization of nitrogen fertilizer were generally low compared to other experiments, and were highest for the early dry season cropping period.

During a period of dry weather, seedling tea bushes were generally less stressed than the clones which had been derived from those plants by vegetative propagation. There were interesting differences between the clones in their responses to dry conditions, but these could not have been predicted from similar observations made on the heterogeneous seedlings. However, it should be possible to use tests, based on measurements of the xylem water potential and stomatal resistance, to identify potentially drought-resistant clones at a later stage in the selection programme.

The influence of leaf area and inter-plant competition on the growth and yield of a crop of high-yielding dry beans (Phaseolus vulgaris L.) in central Mexico was studied, using density and thinning treatments. The highest seed yield (4210 kg/ha at 14% moisture) was obtained with the highest density (28·8 plants/m2). Thinning showed that pods/plant was sensitive to inter-plant competition between 36 and 78 days after seeding (first flower at 50 days), but seeds/pod, and especially seed weight, were not sensitive. It is suggested that the close positive relation between yield and leaf area duration derives from the influence of photosynthate supply upon pod number.

The efficiency of fertilizer P uptake by irrigated wheat, as affected by method and time of application, was studied in the field by using P32 labelled superphosphate. Fertilizer P was applied at planting in a sideband, with the seed, or broadcast, and broadcast at tillering. Phosphorus applied at tillering was most productive for grain and straw yield, and its utilization was significantly higher than from P applied at planting. Phosphorus broadcast at planting was least efficiently utilized. A high correlation was found between the ratio of fertilizer P to soil P in grain and straw, and with their respective yields.

Plant water potential and leaf diffusive conductance, key features of plant responses to water stress in field experiments, can be estimated, respectively, by xylem pressure potential measured with the pressure chamber apparatus, and leaf permeability measured with the air flow porometer. This paper describes modifications to these two techniques in order to increase the rapidity of measurements in wheat to 60/h with the pressure chamber, and 200/h with the porometer. Rapid measurements are needed because of the large within-and between-plot errors encountered with daytime measurements in typical field experiments, examples of which are presented.

The response of the latest wheat cultivars to irrigation regimes was studied between 1970 and 1975 in a heavy soil of the Yaqui Valley of north-west Mexico. Yield showed greatest sensitivity to water shortage in the period 65–110 days after seeding (spike emergence around 90 days), due largely to responses in grains/m2. More frequent irrigation increased yields 5–10% over the average of 7 t/ha obtained with the commonly-adopted five irrigation regime. Various irrigation criteria were tested: potential evapotranspiration calculations seemed the most useful. Measurement of leaf permeability (with an air flow porometer) showed more promise than the use of plant water potential (measured with a pressure chamber).

Effectively nodulated, pot-grown cowpea plants were irrigated with nutrient solution containing 25 ppm 15N, and the relative contributions to total plant N status of inorganic and nodule-fixed N were determined. Maximum rates of N assimilation occurred during pod-fill, with nodules contributing ten times more nitrogen than the applied source. Symbiotic fixation supplied over 80% of total plant N throughout growth, and contributed significantly to seed N during late pod-fill, when nutrient N assimilation was negligible. Vegetative N content was greatest at mid pod-fill, and mobilization from this 'pool' was equivalent to 44% of total seed N. The implications of these (and previously reported) data are discussed.

By comparing flowered and non-flowered plants of the same age (where flowering was inhibited by photoperiod control), cane yield gains due to prevention of flowering were estimated to be 56·6% in a plant crop and 33·8% in a ratoon crop. Sugar gain due to prevention of flowering was 69·1% in the plant and 35·4% in the ratoon crop. A simple negative linear relation was found between cane (and sugar) yield per plant and the proportion of canes that flowered. There was no significant difference in fibre content of flowered and non-flowered canes. The influence of loss of growth, side-shoot production and pithiness on the yield of flowered canes are discussed.

Studies to determine the effect of planting unshelled pods, using groundnut varieties with different shell thicknesses, indicated that emergence and yield were suppressed by planting unshelled pods. Depth of sowing, and soaking pods in water prior to planting, had limited effects.

The results of eight fertilizer experiments with cotton, conducted in several areas of Macedonia, were evaluated by leaf analysis to establish possible relations between leaf N, P and K and yield, as well as to estimate the adequacy ranges of those elements under local conditions. Such a relation between leaf N and yield does exist, and leaf N within the range 4·4–4·9% of DM is adequate. On the other hand, leaf P and K within the ranges of 0·20–0·29 and 1·5–2·6%, respectively, also seem to be adequate. These findings are in agreement with general experience in this region, where cotton seldom benefits from application of fertilizers other than nitrogenous.

The effect of sowing time and variety were tested for three consecutive years under irrigated conditions. The relation between yield and planting time was quadratic, best described by y=a+bx-ex2 where y is grain yield and x is planting time. The results showed that, irrespective of variety, the optimum sowing date is around mid-November. Varietal differences are related to number of ears per unit area, with a stronger association of yield with grain weight than with any other yield components.