Four methods of measuring crop production are reviewed in the context of different survey objectives. A popular technique, crop cutting, tends to overestimate yields and does not produce good estimates of individual plots. For high accuracy, harvest of the whole plot is the best method. If statistics of regional production are required output can be sampled after harvest, or, if the farmer harvests in consistent units, his own estimate can be taken. Limited evidence shows that farmers' estimates may be no more biased than crop cutting, but require fewer resources and supervision. There is no best method. The method used must be chosen for the purpose of the study. Whichever method is chosen a distinction should be made between biological and economic yield and correction must be made for threshing and moisture content.

As the art of plant breeding became a professional and increasingly expensive activity, legal protection was gradually provided in member states of UPOV (International Union for the Protection of Plant Varieties), at present 17 in number. The requirements and scope for protection by Plant Breeders' Rights (PBR) are reviewed and are considered to be favourable for plant breeders, growers and national agricultural productivity. Advantages and disadvantages of PBR and patent protection in connection with biotechnology, the rôle of multinationals as plant breeders and aspects of genetic erosion are discussed.

In India, sorghum is grown during the post-rainy season on Vertisols with stored soil moisture. As water stress towards the end of the growing season is believed to be a major cause of poor yields in these crops, an experiment was carried out involving five sorghum genotypes and four sowing dates with and without irrigation.

Supplementary irrigation with 40 mm of water in the earliest sown crop increased grain yields by 24 and 26% in 1979 and 1982, respectively, while irrigation with a total of 120mm water in the latest sown crop increased yields by 87 and 60% compared with the corresponding dryland crops. Early sowings always resulted in better stover and grain yields irrespective of irrigation treatment. Grain yields of hybrids were similar to those of the cultivars but their stover yields were less. The post-rainy season cultivar SPY 86 gave the best grain yield across sowing dates. The widely grown post-rainy season cultivar M 35–1 yielded less but produced more stover and its yields were more stable. The importance of the stability of grain and stover yields and of evaluating the materials for more than one date of sowing in selecting sorghums for the post-rainy season is discussed.

Sixteen years' yield and growth data from an oil palm planting experiment, comparing 56, 110, 148 and 186 palms ha−1, and additional records from a progeny experiment, were used to study the effect of palm age and planting density on carbohydrates incorporated in total above-ground dry matter production per palm (TDMc) and its components: fruit bunch yield (Yc) and vegetative growth (VDMc). The canopy efficiency (e), the amount of carbohydrate incorporated in dry matter production per unit of absorbed radiation per hectare, decreased from the fifth to eighth year then levelled off, but increased once crown expansion was completed. The decrease in e paralleled the expansion of the intercepting leaf surface, and might therefore be linked to an increase in maintenance respiration losses. These losses were apparently not compensated for by an increase in photosynthetic production. The subsequent increase in e in older palms appears to have been due to improved light distribution as a result of an increase in light penetration. The effects of changing levels of light interception and distribution on e were more pronounced at higher density, and resulted in marked differences in changes of TDMc with age between densities. Corresponding differences occurred with Yc, so that the optimum density for current yield decreased until 12 to 13 years from planting, then markedly increased. These findings are discussed in relation to the measures which might be used to increase yield per unit area.

Yield and growth records from an oil palm planting density experiment, comparing 56, 110, 148 and 186 palms ha−1, and a progeny experiment, planted at 115 and 143 palms ha−1, were used to estimate the partitioning of assimilates into those used for structural dry matter (DM) production, and those used for growth and maintenance respiration.

Gross photosynthetic assimilation (A) for closed canopies was estimated from absorbed photosynthetically active radiation (PAR), derived from actual sunshine hours, and the assimilation-light response curve, to be 128 t CH2O ha−1 year−1. A for non-closed canopies was calculated by correcting for the degree of light transmission, which in turn was estimated from recorded leaf area index values (L), i.e. the total leaf area per unit ground area.

Forty-eight percent of gross assimilation was used for DM production, about half of this being lost in growth respiration. The remaining 52% was lost in maintenance respiration. These losses appeared to level off before crown expansion was completed, and since trunk biomass continued to increase, maintenance respiration per unit biomass (R) decreased with age.

An increase in planting density reduced the assimilates available for bunch DM, had little effect on those for vegetative growth, but strongly reduced maintenance respiration and, since biomass was little affected, reduced R. Assimilates for bunch DM ha−1 reached a maximum at L = 5.6.

The observed trends in R as a function of palm age and planting density merit further study.

The effects of various intercropping patterns of maize and melon on soil temperature and moisture content and crop growth and yield were compared in field trials over a two year period. Intercropping raised soil temperature in the upper 10 cm at 0600 h and reduced it at 1000, 1400 and 1800 h, and also increased soil moisture content by about 30%, compared with maize sole cropping. Melon biomass and seed yields were reduced by intercropping but maize growth characters were unaffected. However, the reduction in melon yields was less when grown with maize in widely spaced rows. Maize intercropped with melon in alternate pairs of rows (2:2) gave the best land equivalent ratio (LER).

Genotypes of mung bean commence flowering at very different times depending on sowing date and location, but relatively little is known about the modulation of flowering by environmental factors. Previous and frequently cited conclusions have been that: (a) genotype, photo-period and temperature all interact to determine relative earliness to flower, and that (b) the genetic control of these photothermal responses is seemingly complex. However, our reanalyses of original data in terms of rates of progress towards flowering, 1/f, rather than the traditional approach based on days from sowing to flowering, f, show that the photothermal modulation of flowering in mung bean can be described by a series of simple, linear models, and that interaction terms involving photoperiod and temperature are often insignificant. The merits and implications of this alternative analysis and interpretation of original data are discussed.

A long-term field study was conducted from 1979 to 1985 in the Karnal district of Haryana, India to evaluate the effect of three rates of gypsum (0, 5.2 and 10.4 kg ha−1) on the performance of five grasses (Diplachne fusca, Panicum laevifolium, P. antidotale, Chloris gayana and Cynodon maritimus) on an extremely sodic soil with an initial pH of 10.6 and an exchangeable sodium percentage (ESP) of 94. Diplachne, Chloris and Cynodon usually gave their maximum yield in the second year of planting, P. antidotale in the third year and P. laevifolium in the fourth year. The results showed that Chloris can be recommended for such situations as it maintains a higher productivity over a longer period than the other grasses. Alternatively P. antidotale and P. laevifolium can be planted in association with Diplachne to provide a steady forage supply for a long time. Increasing doses of gypsum resulted in decreases in soil pH, exchangeable sodium and ESP and increases in calcium, magnesium, organic carbon and the infiltration rate of soil.

The tuber yield of potatoes in a field experiment conducted at Jalandhar between 1981 and 1984 was greater following green manuring with either Crotalaria juncea or Sesbania aculeata than after fodder crops of Zea mays or Pennisetum typhoides. The residual effect of phosphorus applied to potato on subsequent wheat crops varied with the previous green manuring and fodder cropping treatments but was always sufficient for the wheat when applied at an economic rate; the lack of an application of phosphorus fertilizer to the wheat did not result in a decline in the availability of soil phosphorus. The use of C. juncea as a green manure increased the availability of phosphorus but decreased that of potassium. Pennisetum typhoides also depleted soil potassium reserves. Sesbania aculeata green manure improved the organic carbon status of soil whereas P. typhoides depleted it.

In spite of large year-to-year variations in clove yields, production in the islands of Zanzibar and Pemba is often in synchrony and the annual harvests of the two islands are correlated with similar variables. Clove harvests are positively correlated with rainfall in October to February two years before the harvest and negatively correlated with the harvest in the previous year and rainfall around July, and October to December of the year before the harvest. It is likely that rainfall in these periods affects vegetative growth of the clove tree and clove bud differentiation.

In sub-tropical India where 70% of the country's sugarcane is grown, companion cropping of wheat in autumn-planted sugarcane is beneficial. However, because the yield of sugarcane is reduced, farmers there are reluctant to adopt this cropping system in spite of the greater monetary gains compared with wheat-sugarcane sequential cropping. Application of 200 kg nitrogen ha−1 to sugarcane in two doses, two-thirds immediately after the wheat harvest and the remainder a month later, combined with irrigation at 75% available soil moisture during the summer months (April–June), produced cane yields similar to those from sole autumn-planted sugarcane, with an additional 4.8 t ha−1 of wheat.

Field experiments were performed in 1981 and 1982 on the cotton cultivar Giza 75 to determine the effect of different concentrations and application dates of the defoliant Harvade on the lint, seed, protein and oil yields, and oil properties of cottonseed. Defoliant concentrations of 240, 360 and 480 ml ha−1 increased lint yield per plant but tended to decrease seed index. Cottonseed yield per hectare, seed oil and protein percentage and yield, oil refractive index, free fatty acids, saponification and iodine values were not significantly affected by the defoliant. Late application increased lint yield per plant and cottonseed, oil and protein yield per hectare. Date of application had no effect on seed index, seed oil and protein percentage and oil properties.