In field trials a population of 61,700 maize plants/ha produced higher total dry matter and grain yields than the conventional 36,000 plants/ha. There was no difference in yields with inter-row spacings of 45, 60 or 90 cm, regardless of population levels. Weed suppression was increased by the higher population even though the entire experimental area was treated with herbicides. In one of three years perennial sedge and annual weed growth started 4–5 weeks after herbicide application, under which conditions row spacing had a greater effect and weed growth was significantly less with 45 or 60 cm maize rows than at 90 cm.

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.

Nitrogen fertilizer requirements and potential forage yield of maize and two millet types grown under irrigation in Saudi Arabia were assessed. Nitrogen application at 50 kg/ha produced mean yields of up to 15.7 t/ha in maize variety Pioneer H.3147. Splitting the nitrogen application did not significantly affect yield. Nitrogen above 100 kg/ha did not significantly increase DM yield of Proso millet (Panicum miliaceum). Mean total DM yields of 17.6 t/ha of Setaria italica were produced, after 111 days, with 150–200 kg/ha of nitrogen; 150 kg/ha of P2O5 produced a mean DM yield 7.9% higher than 75 kg P2O5/ha.

A field experiment was conducted on a Zn-deficient highly-deteriorated sodic soil of the Ghabdan series to determine the effect of three rates of gypsum (G0, G25, G50% of the gypsum requirement of soil) and three rates of Zn (Zn0, Zn11, Zn22 kg Zn/ha) on rice variety PR 106. Gypsum application significantly increased yield and Zn uptake in rice because of a significant decrease in soil pH and increase in Ca and Zn supply. Zinc application alone significantly increased soil and plant Zn but yields were poorer than with gypsum application alone because of Ca deficiency/Na toxicity. The same rates of Zn applied together with gypsum markedly increased yield and Zn uptake, revealing a deficiency of both Ca and Zn. The best grain yield was recorded either at G50Zn11 or G25Zn22, indicating an economy in gypsum at higher rates of Zn or of Zn at higher rates of gypsum application.

The response of Italian ryegrass (IRG) to nitrogen fertilization, irrigation frequency and harvest interval indicated that management of nitrogen and water is the determinant of productivity under semi-arid northern Mexican conditions. Where water is non-limiting the effects of harvest interval can be eliminated. A soil moisture balance model indicated the inadvisability of seeding IRG in sandy soils if water is a scarce resource because of the high frequency of irrigation that would be required. The seeding (September) and late production (April) periods were identified as critical in regard to irrigation need and limiting in terms of the area that it would be possible to seed.

In three field experiments, peat pH increased in parabolic relation to liming at the rate of 0.0544 pH unit/t/ha between 0–40 t/ha lime, but only 0.0224/t/ha between 40–72 t/ha. Groundnut and sorghum seed yield and crop residue also showed parabolic responses to peat pH and liming, but groundnut seed yield correlated poorly with soil pH (r2 = 0.38, P = 0.05), compared with its crop residue as well as with sorghum seed and residue (r2 = 0.75, 0.76 and 0.79, respectively, P = 0.01). Groundnut was generally more tolerant of peat acidity (pH 3.35–3.65) than sorghum, giving higher plant survival in unlimed plots, optimum seed and residue at pH 4.60 compared with 5.70 for sorghum, and reduced responsiveness to pH increase. Seed and residue of both crops decreased with continuous cropping, probably because of increasing pest and disease incidence and depletion of available soil nutrients.

Results are described of an experiment conducted for 2 years in North-West India where grain legumes increased the N and P status of the soil compared with cereal or fallow. Maize following legumes recorded increases in growth, yield attributes, yield and N uptake. Various winter grain legumes such as chickpea, lentil, pea and Lathyrus sativus reduced the need for fertilizer N in maize to the extent of 18–68 kg/ha compared with cereal (wheat) or fallow. Application of nitrogen to the maize promoted plant growth and increased both yield and N uptake.

Boron treatment was superimposed on half of 48 Amazon cocoa NK-treated plots in four locations across Southern Nigeria. Boron was deficient in soil and leaves of untreated 12-year-old Amazon cocoa, but boron treatment increased bean yield from 13 to 70%. Application of N and K fertilizers reduced the impact of soil-applied boron.

The total growth increment of sugar cane stalks from 13 to 22 weeks after planting was 55% greater in elevated than depressed areas in fields flooded intermittently during the period of measurement. The weekly growth increments were 137–9% greater in elevated than depressed areas, especially when soil moisture was high. The cane was on top of high ridges but water stood up to 10 cm deep over the top of the ridges in depressed areas for up to 5 or 6 days after rain and at varying depths below the top for several more days. Provided the soil was not submerged, tillers elongated most when the soil profile was saturated or nearly so; mere waterlogging without submergence seems not to damage cane. Tiller elongation and soil moisture were well correlated regardless of depth of sampling between 0 and 45 cm, but different relations were obtained for elevated drained areas and depressed areas subject to submergence.

An intercropping experiment is described, using a parallel-row systematic design, to examine four plant populations of chickpea in all combinations with 15 systematically arranged populations of safflower in 1:1 and 2:1 row arrangements; four populations of the sole crops were included. Safflower was usually dominant and increasing the total population (i.e. both crops combined) made it more so. Safflower yield was little affected by changes in its own population and was independent of changes in the chickpea population. Chickpea yield increased with increase in its own population and it was the dominant crop at high chickpea/low safflower populations. An initial increase in safflower population caused an increase in chickpea yield at the 1:1 row arrangement; otherwise increasing safflower population decreased chickpea yield. LERs at 2:1 indicated no real evidence of yield advantages for intercropping. At 1:1 advantages ranged up to 19%, with a maximum where the highest chickpea population was combined with a low safflower one. This optimum combination could not have been identified with earlier designs.

Puncture tapping and one-eighth spiral (S/8) tapping, both combined with Ethrel stimulation, were compared with conventional half spiral (S/2) tapping of immature Hevea trees. Stimulated puncture-tapped trees in some experiments yielded more rubber and had much more sucrose in the latex than unstimulated half-spiral tapped trees. Yields of puncture-tapped trees also increased with increase in the quantity of Ethrel and the number of punctures, but were not affected by the size of puncture. Girth increments of the trees and percentage dry rubber content of the latex were approximately equivalent in all three methods of tapping.

In three field experiments studying the liming needs of cassava on peat, optimum tuber DM was obtained at pH 3.8 and optimum top DM at pH 4.2; liming to higher pH values decreased tuber DM while maintaining top DM. Consequently, the Harvest Index decreased over the whole range of soil pH studied (3.49–5.50). Increases in tuber DM per hectare with liming, and with an increasing growth period, were associated with mean tuber weight (r = 0.86) and with Harvest Index (r = 0.65) rather than with tuber number (r = 0.37).

A hydraulic press (the J-14) was compared with a Scholander pressure chamber to measure leaf water potential in Theobroma cacao, Gliricidia maculata, Cajanus cajan and Elaeis guineensis. Although the press satisfactorily estimated water status in soft, unhardened leaves of T. cacao, G. maculata and C. cajan at high water potential, it underestimated water status in hardened leaves of T. cacao. Satisfactory estimates were obtained at low water potential for hardened leaves of T. cacao but not for the others. There was a poor relation between readings of the two instruments for E. guineensis over a wide range of water potentials because press readings appeared to be influenced by leaf structure.

Inoculating Zea mays (three cultivars), Sorghum bicolor, Panicum miliaceum and Setaria italica with nitrogen-fixing bacteria of the genus Azospirillum in Northern Negev and Bet Shean Valley field experiments resulted in significant increases in yield of grain and foliage of commercial value. It was concluded that inoculating summer cereal crops in Israel may save valuable nitrogen fertilizer.

Land Equivalent Ratio (LER) and cowpea growth attributes were used to evaluate three different maize cultivars for intercropping with cowpea, a low canopy crop. The relatively short maize cultivar (Kewesoke) with erect upper leaves transmitted the most light to cowpeas, followed by a liguleless erect-leaf type and then a floppy-leaf type. The more the transmitted light, the greater were the growth and yields of associated cowpeas.

Field experiments were conducted for 3 years covering 4 crop seasons at Lucknow to study the utility of pigeonpea (Cajanus cajan) as an intercrop in economizing N for maize (Zea mays) and to assess the residual fertility of kharif crops on autumn-planted sugarcane (Saccharum officinarum). Pigeonpea increased the soil N content due to substantial nodulation, but as an intercrop it did not increase the yield of maize at any level of nitrogen. Sugarcane grown after pigeonpea yielded 43% more than when grown after maize. Intercropping pigeonpea in maize would be more beneficial than growing a pure crop of maize before planting sugarcane.

Gibberellic acid (GA) at 1500 ppm, applied as foliar spray or pre-plant soak, effectively promoted flowering in Nigerian clones of the cocoyams Xanthosoma and Colocasia. A foliar spray (technical grade GA) applied with 0.25% surfactant gave better results than with 0.01% surfactant or than a foliar spray of Pro-Gibb Plus (commercial GA formulation). A pre-plant soak of Pro-Gibb Plus was least effective but could be useful in poorly equipped research stations.

An experiment was conducted during the 1978/79 summer at the Central Cotton Research Institute, Multan-Pakistan to evaluate the crop production patterns of two cultivars of cotton (G. hirsutum L.) differing in their reaction to heat-induced sterility. Boll set in variety ST3 amounted to 7.7% of the total fruiting points, from flowers opening during the hottest months of June, July and early August, while almost all the fruiting points produced by cultivar B557 during the same period were shed and no bolls were set. Of the flowers examined during July, 83.3% in B557 contained non-dehiscent anthers against 6.7% in ST3.

Using the sugar cane cultivar Co 421, competition from weeds for the whole growing season was compared at three row spacings with competition for periods ranging from 15–120 days at the start of the season or later, and weed-free conditions all through the season. The critical period for weed competition was the first three months, since weeding during the remaining 11 months did not improve yields, which were similar at row spacings of 1, 1·25 or 1·5 m. There were no interactions between the weeding and spacing treatments.

The parasitic weed striga had significantly greater effects on sorghum yield components than non-parasitic weeds. Grain reduction caused by striga amounted to 65% compared with 32% reduction caused by non-parasitic weeds. Comparable reductions were also manifest in straw yield, grains/head and plant height of sorghum. Early removal of striga (a week after its emergence), and thereafter at regular weekly intervals, may help to improve crop yields.