Two sets of experiments examined the effects of weeds on maize yields using weeding methods typical of small farms in Zambia where oxen are used for cultivation. Maize yield losses of 30% due to weeds were evident with common weeding practices. A critical period of competition, during which the crop should be kept clean, was demonstrated from 10 to 30 days after emergence. This is a period of peak labour demand and the prospect of using chemical weed control to ease the situation is considered. The value of weed competition data, given its variability between sites, is discussed.

A replicated field study was conducted during 1979 and 1980 in the Karnal district of Haryana, India to investigate the effects of three rates of gypsum (0, 5.2 and 10.4 t ha−1) on the performance of five forage grass species (Rhodes grass (Chloris gayana), blue panic (Panicum antidotale), Panicum laevifolium, Karnal grass (Diplachne fusca) and coastal Bermuda (Cynodon dactylon)) on an extremely sodic soil. The soils used had a large exchangeable sodium concentration and pH in the top 15 cm (94% and 10.6, respectively). For comparison, the same grasses were also planted in a normal soil. The results showed that the relative tolerance of these species to increasing sodicity was in the order of Karnal grass > Rhodes grass > coastal Bermuda > blue panic ≥ Panicum laevifolium.

Experiments in Brazil have shown that a sorghum-pulse (cowpea or common bean) intercrop system yielded more grain than the monocrop system and produced a Land Equivalent Ratio (LER) greater than 1.00 even though rainfall was limited. Sorghum competed less than maize with the associated pulse when Competitive Ratios (CR) were considered. In cowpeas, CR values were correlated positively with the number of pods and seeds plant−1. The two crops in the intercrop systems were responsive to fertilizer application. Thus, improved management (i.e. fertilizer usage) was appropriate without the loss of the advantageous effects realized from intercropping.

The dependence of yields of sweet clover and alfalfa on environmental conditions, including soil acidity, at the germination stage has been studied over a period of 28 years. Results have been dramatic: sweet clover and alfalfa can grow well and produce large yields even on strongly acid soils (pHKCl 4.0) providing that the process of germination starts in a neutral medium.

In a 2 row cereal: 1 row pigeonpea intercropping system, four sorghum and two millet genotypes were examined with four of pigeonpea on a medium-deep Alfisol during 1978 and 1979. The cereals usually produced a large proportion of their sole crop yields. Millets matured relatively early which allowed large yields of later-maturing pigeonpea. A tall millet gave the best total Land Equivalent Ratio (LER) of 1.78 and most monetary returns. Early and/or short sorghums produced large LERs (1.51–1.59) and combinations with an early hybrid also gave good returns. A tall late sorghum gave poor yields of both components, smallest total LER (1.30), and little return. Pigeonpea intercrop yields became larger as the maturity difference between the cereal and pigeonpea increased. A combination of a short, early but large-yielding cereal with a pigeonpea that is as late as possible without incurring undue risk of moisture stress may be ideal.

The Boro (dry) and Kharif (wet) seasons of West Bengal differ appreciably in respect of atmospheric temperature, relative humidity and hours of bright sunshine each day. Post-harvest hot temperature (31°C) either in controlled conditions (in the Kharif season) or in natural (31.5°C) conditions (in the Boro season) had a more significant effect than post-harvest cool air temperature (20.4°C) in the Kharif season on the early breaking of dormancy of paddy rice seeds. However, the pre-harvest hot air temperature (31.4°C) of the Boro season was no more effective in breaking dormancy than the pre-harvest cool air temperature (20.9°C) of the Kharif season. With a mean air temperature of 20.4°C the post-harvest exposure of the seeds to the sun from sunrise to sunset during the Kharif season was much more effective in breaking dormancy than the post-harvest mean air temperature of 31.5°C during the Boro season.

Three cowpea cultivars were grown in the dry season on an inland valley swamp. Rice straw was used to mulch the plots and all seeds were pelleted with nitramolybdenum before planting. Fertilization with N, P and Mo and cultivar differences affected pod production and seed yield, but differences in plant population or inoculation with Rhizobium did not affect nodule weight, pod no. m−2, pod weight or seed yield significantly. Seed yields of 0.91 t ha−1 from an improved cultivar and 0.83 t ha−1 from the local type were obtained. Even with heavy mulching there could be variations in seed yield in undeveloped inland valley swamps because of changes in microrelief.

Accumulation curves for N, P, K and Ca were determined for intercropped maize and cowpeas given different fertilizer combinations. Both species competed for these four elements, with cowpeas suffering relatively more than maize. A concept of a Nutrient Supplementation Index (NSI) was developed to aid studies on fertilization of crop mixtures. Using this index, it was estimated that an additional 9.7, 24.0, 9.7 and 30.6% of N, P, K and Ca, respectively (based on the requirement of sole-crop maize), might be needed to satisfy the combined needs of a 1:1 row maize–cowpea intercrop.

Thirty-two Prosopis accessions were studied and biomass production (dry matter) determined for 27 of them, which were irrigated when the soil moisture tension reached 60, 200, or 500 kPa. Three seasons after transplanting (i.e. after 2½ years) the trees were harvested, weighed, and sub-sampled for moisture content determinations. Little difference was observed in productivity among irrigation treatments. A 20-fold range in biomass productivity occurred among accessions; Prosopis chilensis (0009) from Argentina gave the greatest production of 13.4 t ha−1 a−1. The water use efficiency of US rangeland accessions ranged from 2300–2600 kg H2O kg dry matter−1. P. chilensis (0009) in the driest irrigation treatment had a water use efficiency of 345 kg H2O kg dry matter−1.

Nodulation and N2-fixation of groundnut were investigated in sole and intercropping systems. Intercropping with pearl millet, maize, or sorghum reduced nodulation and N2-fixation. This effect is ascribed to the shading of groundnut by the cereal component and the consequent decrease in photosynthesis of the legume canopy.

Groundnuts (Arachis hypogaea L.) are generally considered to be self-pollinated, but natural hybrids due to outcrossing have been observed in cv. Robut 33-1. Selections in segregating generations of these natural hybrids identified stable lines with large yield potentials in more than one environment. The role of natural hybrids in generating useful additonal variability is discussed.

Field experiments investigated the effects of seed rate, row spacing and time of harveston growth and yield of irrigated fibre flax and economics of fibre production at the Experimental Farm, Palampur, North Western Himalayas during two winter seasons between 1979and 1981. A seed rate of 60 kg ha−1 and row spacing of 20 cm gave the best yield and most profit. Any delay in harvesting after flower initiation significantlyincreased fibre yield and net profit per hectare.

Three levels of nitrogen (N) were applied to cotton grown in irrigated field trials at two locations in Zimbabwe in 1978. Dry matter (DM) production, total uptake and distribution of N among vegetative and reproductive components, and soil mineral-N contents were recorded about every 14 days. About 60% of total DM was produced, and 40% of total N taken up, between 10 and 16 weeks after sowing. Most N was present in vegetative parts, particularly leaves and branches, during early growth but, later, it accumulated in buds, flowers and bolls. At maturity, seeds and lint contained 42% of total above-ground plant N. N concentrations were similar in sympodial and mainstem leaves, petioles and branches. Inorganic N applied at sowing had little effect on plant N, but when given after 10 weeks it increased the N content of leaves, stems, branches, petioles and bolls.