Two different collections of local sorghum strains, grown in 1975/76 and 1976/77, showed considerable and useful variation in plant height at maturity, head type and exsertion, grain colour, and days to flowering and maturity. A close and positive correlation was found between days to flowering and to maturity, and x2 tests also showed close associations among other characters. Implications of these variabilities for sorghum improvement are briefly 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.

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.

A field experiment evaluating criteria for scheduling wheat irrigation was conducted from 1975 to 1977 in a sandy loam soil with treatments scheduled according to physiological stages, soil moisture conditions, pan evaporation and leaf water potential. Grain and straw yields, spikes/m, fertile spikelets/spike and number and weight of grains/spike were significantly influenced by treatments. Irrigation based on leaf water potential was as good as when based on physiological stages or soil moisture, and the use of pan evaporation was no better than other methods of scheduling.

The use of fertilisers in maize production has been the focus for many years of agronomic studies on research stations in East Africa. However, information on production risks and profitability of fertiliser use on smallholder farms is generally lacking because most of the early studies have focused on mean yields and yield components on research stations. This study applied rigorous analyses to determine conditions under which (1) production risks are low; (2) the recommended nitrogen (N) and phosphorus (P) fertiliser rates achieve a yield target of ≥3 t ha−1 believed to be a necessary condition to kick start a smallholder-led ‘green revolution’ in Africa and (3) N and P fertiliser use is profitable on smallholder farms in East Africa. Analysis of data from 464 on-farm trials in Kenya, Rwanda, Tanzania and Uganda revealed significant variations in production risks and nutrient use efficiency with season and soil type. On most sites, except in Uganda, production risks were lower with the recommended N and P fertilisers than the control during both the short and long rains. Production risks were three to four times higher with N and P fertiliser relative to the control on Lixisols and Ferralsols, but such risks were much lower on Nitisols, Leptosols, Vertisols, Plinthosols and Cambisols. The probability of exceeding grain yields of 3 t ha−1 with the recommended N and P rates was over 0.60 on Nitisols and Leptosols, but less than 0.20 on Lixisols and Plinthosols. The agronomic use efficiencies of N (AEN), P (AEP) and value cost ratios (VCR) were highest on Cambisols and lowest on Plinthosols. The VCR increased linearly with increase in AEN (R2 = 0.92) and AEP (R2 = 0.87) and less so with increase in grain yields (R2 = 0.47–0.60). Net present values indicated profitably of N and P fertiliser over the long term in only 30% of the site by season combinations in Uganda compared with 69% in Kenya, 81% in Rwanda and 84% in Tanzania. Patterns of N use efficiencies were different from P use efficiencies across soil types. Therefore, we recommend that N and P fertilisers should be appropriately targeted to soils where applied nutrients are used efficiently by maize crops.

A number of crosses were made to study the mode of inheritance of flower colour and number of locules per capsule of sesame. Red flower colour was dominant to white, and 4-loculed dominant over 8-loculed pods, each of the traits being controlled by a single gene pair segregating in a 3:1 F2 ratio.

A field experiment to study weed and fertility management in rain-fed maize was undertaken at the Palampur Experimental Farm during the wet seasons of 1977 and 1978. Intercropping soya-bean in maize did not impose undue competition and significantly increased net profit per ha. Yields and net returns were significantly higher when weeds were controlled and 80 kg N/ha was applied. Increased application of fertilizer without weed control did not alter the yield of maize, and there was no response to phosphorus. Various yield attributes of maize were significantly affected by weeding and nitrogen treatments through their effects on grain and stover.

Genetic engineering of crop plants has been in progress since the dawn of agriculture, about 10 000 years ago. For millennia the genetic make-up of our crop plants has been changed by mankind's selection of naturally occurring variants. As the trade routes were developed, novel plant types were introduced into new environments and provided more variation from which to choose. At the end of the nineteenth century an understanding of the laws of heredity was gained and plant breeding protocols were devised whereby selection became accompanied by deliberate crossing. As the knowledge of the genetic structure of crop plants improved, new ways of manipulation were invented and exploited. Indeed plant breeding became a testing bed for new ideas in genetics. For the plant breeder the techniques which were most widely employed in the past were those which aided breeding, for example techniques which speeded up the production of new varieties, but still used traditional routes of crossing and selection. This was a transitional phase between plant breeding as an art and plant breeding as a science.

Field experiments were conducted for 4 years to study the yield of ‘kharif’ and ‘rabi’ crops grown in sequence on two soils differing in water-holding capacity. The results indicated that drought caused greater reduction in yield of rainy-season crops on loamy sand than on sandy loam soil. In low retentivity soil it was more profitable to raise a single crop of wheat on soil-stored water. In sandy loam soil of higher retentivity, two crops a year gave much higher yields than a single crop. Of the sequences tried, maize followed by wheat gave the highest and most stable yields. For ‘rabi’ crops, stored water showed a better yield response than an equivalent amount of rain during the growing season.

Effects of moisture stress during different stages of cotton development were evaluated by using correlation and regression methods on data of six irrigation experiments from three different climatic regions. Significant negative correlations were found between the number of days in which soil moisture was below a threshold level, and several plant traits. Flower number was usually affected adversely by stress at the beginning of flowering; boll number, boll retention, boll weight, lint yield, lint length and seed index by stress at the end of flowering; earliness and lint fineness by stress during early boll development. Lint index, per cent and strength were affected by stress at different periods and effects of stress on lint yield were correlated with its effects on boll number, boll weight, lint length and early maturity.

Studies of seed pelleting and liming for legume establishment at initial low pH levels in prepared seedbed and natural pasture situations were conducted in 1971 and 1972 at Rio Grande do Sul, Brazil. Lime-pelleted seed often improved establishment and increased subsequent dry matter herbage yield of soybeans, greenleaf desmodium, and perennial soybeans at low pH levels (4·8 and 4·9) and low lime rates. Applying agricultural lime at rates up to 6 t/ha generally improved legume establishment and herbage yields on prepared land or in disked natural grass sod, compared to unlimed areas.

Dry matter production in a bushy and spreading cultivar of sweet potato was studied in two trials comparing dry matter partitioning between plant components. The bushy cultivar, VSP-2, accumulated more tuber dry matter than the spreading cultivar, BNAS-51. The number and yield of tubers of VSP-2, was also greater but its foliage dry weight was less than that of BNAS-51. The vine and root dry weight of BNAS-51 increased with time but that of VSP-2 reached a peak about 10–12 weeks after planting. The tuber dry weight of BNAS-51 at harvest was similar to its foliage dry weight but that of VSP-2 was three times greater. The proportion of total dry matter partitioned to the tubers of VSP-2 was greater than that in BNAS-51 at all stages of growth.

Experimental Agriculture (1997), 33, 367–383.

An incorrect version of Fig. 1(b) was published on page 373 of the above mentioned paper. The correct version appears below. The publisher apologises for this error.

A field experiment was conducted during the monsoon seasons of 1982 to 1984 to investigate the effect of chlormequat chloride (CCC) and its mode and time of application on groundnut. Foliar application of CCC 60 days after sowing at the rate of 200 ppm reduced moisture loss and increased relative leaf water content and yield. Soaking seed in a 0.5% CCC solution also increased relative leaf water content, root nodulation and seed yield.