In the preceding paper in this series (Pearce, 1992) it was explained how an experimenter can ask specific questions about the treatment responses and can obtain answers to them by using contrasts of interest. Here, two standard cases are examined, one in which treatments are quantitative in nature, like the amount of fertilizer applied or the dates on which spraying takes place, and the other in which the treatment set is formed from all combinations of two or more other sets. (Such a ‘factorial set’ might be formed from several kinds of herbicide being used with a range of cultivations.) Finally, a non-standard example is examined in which a well considered set of treatments provided information directly relevant to the subject of enquiry. The subject is considered with some emphasis on testing, but in many instances estimation would be better.

Restriction fragment length polymorphisms (RFLPs) are genetic markers based on cloned molecules of DNA. Using RFLPs, scientists can construct high density genetic linkage maps and locate economically important genes. Once a gene for a valuable trait has been mapped with RFLPs, desirable genotypes can be selected using RFLPs rather than scoring for the trait itself. This is important when a trait is recessive, difficult to score, or obscured by other characters. RFLPs are particularly valuable in mapping genes controlling complex polygenic characters, including those fundamental to crop improvement. The first RFLP maps were developed in crop species primarily important in temperate countries. Now RFLP maps for major tropical and sub-tropical crop species are also being developed.

Pot and field investigations were conducted to study the effects of vesicular-arbuscular mycorrhizal (VAM) inoculation and triple superphosphate fertilization on nodulation, dry matter yield and tissue nitrogen and phosphorus contents of Bradyrhizobium-inoculated soya-bean and lablab bean in the Sudan.

Inoculation of both crops with the VAM fungus Glomus mosseae in clay and sandy soils in pots increased nodulation, dry matter yield and tissue nitrogen and phosphorus contents more than triple superphosphate fertilizer, but even greater responses were obtained from G. mosseae combined with fertilizer. Crop responses in the two soils were similar, despite the large differences in soil physico-chemical properties.

In the field, inoculation of both crops with any of four VAM fungi enhanced nodulation, dry matter yield and plant nitrogen and phosphorus contents more than did triple superphosphate. Gigaspora margarita and Glomus mosseae were superior to Gigaspora calospora and Acaulospora species and resulted in more extensive root infection, especially in soyabean.

Cowpea is an important supplement to the staple diet of maize in Zimbabwe, but its productivity is poor beacuse of pest infestations. This paper reports the results of experiments conducted over two crop seasons on the feasibility of producing a grain crop of cowpea intercropped with cotton to take advantage of cotton's slow initial growth and of drift from insecticides applied to it. Intercropping reduced the yield of cotton by between 11.5 and 73% depending on the type of season and the treatments applied, but the reduction was compensated by the yield of cowpea. The yield reduction was greater in the drier first season and with simultaneous planting of the two crops. Cowpea consistently performed better as an intercrop than as a sole crop, mainly because of the protection it received from the insecticides applied to the cotton.

Sustainable crop production on Rwandan oxisols is limited by widespread soil acidity caused by high levels of exchangeable aluminium. This study was designed to test the effectiveness of an indigenous lime material in counteracting the acidity and enhancing crop yields. Lime application significantly raised pH, exchangeable calcium and effective cation exchange capacity, and reduced exchangeable aluminium and total acidity. Calcium was directly proportional to effective cation exchange capacity (r = 0.962**) and was inversely related to aluminium (r = −0.955**). Consequently, yields of wheat, beans and potatoes, which served as test crops, were significantly increased by liming. Lime at high rates (4–8 t ha−1) had a longer residual effect than at low rates (less than 2 t ha−1), suggesting frequent applications are needed when low lime rates are used. Simple regression analysis showed an increase in pH of 0.154 units and a decrease in exchangeable aluminium of 0.385 meq 100 g−1 for a tonne of lime applied.

A shortage of available labour early in the growing season, when effort is directed to the weeding ofcereal crops, appeared to be a primary constraint to increased forage cropping by smallholder farmers in the semi-arid zone of central Mali. In experiments with millet, the labour requirement for weeding was reduced by an average of 45% when the crop was weeded at two rather than four weeks after emergence. A combination of weeding by hand and by ox-drawn plough or harrow only slightly increased labour productivity compared with hand weeding alone. Both lablab and cowpea produced good yields of forage when sown in mid July, but average yield declined by 71 kg ha−l for each day's delay in sowing between mid July and mid-August. Green gram was also productive over a two month growing period and appeared to have potential as a late-sown forage crop.

Inoculation with vesicular-arbuscular mycorrhizal fungi (VAMF) improved growth of chick-pea (Cicer arielinum L.) and doubled phosphorus (P) uptake at low and intermediate levels of P fertilization in a pot experiment on sterilized low-P calcareous soil. In field experiments at Tel Hadya, northern Syria, growth, shoot P concentration and seed yield of spring-sown chickpea remained unaffected by inoculation with VAMF or by P fertilization. The mycorrhizal infection of chickpea was high (approximately 75% of root length mycorrhizal at the flowering stage) irrespective of inoculation with VAMF or P fertilization and may ensure efficient P uptake under field conditions.

Because of shortages of oxen for mouldboard ploughing, delayed planting of maize is common in Mangwende, Zimbabwe and reduces grain yield by 32%. On-farm experiments over four years tested the possibility of using a ripper tine, with atrazine herbicide, to allow smallholders to plant maize earlier. Compared to mouldboard ploughing, tine cultivation increased grain yield at 13 out of 18 sites. All these sites had less than 240 mm of rainfall in January (which coincided with crop anthesis) and long term rainfall records suggest tine cultivation should raise yields in two out of three years. Handweeding and atrazine treatments gave similar grain yields when used with tine cultivation, provided weeds were controlled within 14 days of crop emergence. Tine cultivation was economic at sites where the yield was greater than that with the mouldboard plough. The farmers could manage the combination of tine and atrazine use on a field scale.

This paper uses survey results to show how one group of small scale farmers in Santa Cruz, Bolivia, were able to mechanize annual cropping despite a farming systems diagnosis which indicated that this was not a viable development path. It attempts to identify the underlying causes of farmer success and diagnosis failure.

Grassland productivity was studied for four years near Terbol, Lebanon. In the first year pasture availability and plant numbers were monitored along transects, and in the following three years the effects of sowing four Mediterranean annual legumes (three cultivars of subterranean clover and a local ecotype of Medicago rigidula) and top-dressing with super-phosphate were studied. The results indicated that natural grasslands were dominated by annual grasses (Aegilops, Hordeum, Bromur, Lolium and Poa). Legume density was low, which resulted in poor legume productivity, especially in winter. Exotic legumes only resulted in a slight improvement in pasture productivity even when phosphate fertilizer was added. However, partial protection from grazing (for one or two months in late winter and spring) more than doubled the number of legume seeds in the seed bank compared with full protection and open grazing. The build up of seeds in the soil is an essential step towards the improvement of productivity in these degraded pastures, which form a large part of the land surface in Lebanon and on which small ruminant production largely depends.

Groundnut (Arachis hypogaea) has very great economic importance in Cameroon. In pot experiments, groundnut yields on highly acidified but limed soil were 50% greater than those on unlimed soil. These results demonstrate that severely acidified soils of the western highlands of Cameroon should be limed at moderate rates to sustain crop productivity.