The single-liquid infiltration method of measuring stomatal opening was adapted as a practical field method for determining the time of irrigation of cotton. A number of different liquids, leaf positions and times of measurement were tested and the most sensitive method was selected on the basis of the results. No stomatal response was found while soil moisture was depleted to one-third of available water. A steep reduction in stomatal opening was observed with further drying of the soil. Some results are presented from an irrigation experiment where irrigation control by infiltration method was compared with other methods. The practical possibilities in the use of the method in field practice are discussed.

Castor beans grew well in sandy soils in U.A.R. where field crops had previously failed to produce good yields. Calcium nitrate up to 300 kg. per feddan resulted in increased yields of seeds and oil in a two-year experiment. Better yields were obtained by increasing the number of plants up to 3 per hill at distances of 45 cm. apart. The oil percentage and other properties were not influenced by nitrogen fertilizers or plant density.

Field experiments in three successive growing seasons (1963–66) studied effects of variety and plant density on yield components of broad beans. In 1963/64 total seed yield of a local variety (Beladi), increased with increasing seed rates from 70 to 280 lb per feddan, but yield increment diminished beyond 140 lb. The same results were obtained with Beladi and Rebaya 34 in 1964/65 and 1965/66, but Rebaya 34, yielded less than Beladi at all seed rates. Growth analysis revealed that Rebaya 34 had greater growth rate at the beginning of the season, due to its relatively large seed size, but eventually Beladi overtook it. Maximum pod growth in both varieties occurred when leaf dry weight was declining. The proportion of dry matter was greater in pods of Beladi than Rebaya 34 because of more sinks in the former variety. The present seed rate of 70 lb per feddan seems to be suboptimal and factors affecting establishment and/or effective leaf area at the time of pod growth are detrimental to the final yield.

Cross-inoculation tests, based on nodule formation and nitrogen fixation, were made on 21 species of legumes commonly found in the Sudan. The results showed that they may be grouped according to the accepted system of classification, but there were some important inconsistencies in the cowpea group. For instance, Arachis hypogaea and Acacia spp. have their own strains of Rhizobium. The cultural and physiological characters of the rhizobia studied were generally similar to those known for other species of the organisms.

The results are reported of pot experiments, using indicator plants, on the nutrient status of three soils varying in fertilizer history. All soils were deficient in nitrogen, and in the absence of added nitrogen yield of grass was below 10 per cent of the potential. All forms of nitrogenous fertilizers were equally effective. All soils showed an acute deficiency of phosphorus at the early stages of the experiments, but with time, and depending on the amount of fertilizer applied in the past, the response to phosphorus decreased. There was little or no response to potassium at the early stages of the experiments, but relative yields later fell linearly with time. Calcium was necessary in small quantities as Ca(OH)2, CaCO3 to correct soil acidity, particularly for legume growth. Magnesium increased yields at the latter stages of the experiments. Sulphur was deficient in all soils. The soils had adequate amounts of the minor nutrients. A cheap and quick technique was used with simple and factorial designs to obtain preliminary information, as a guide to planning detailed field experiments on the nutrient requirements of perennial crops like coconuts and other intercrops.

To investigate seasonal effects on nodulation of legumes during an English summer, plants of Pisum sativum and Phaseolus vulgaris were sown in pots in the open at intervals of 14 days between March and July and the pots were watered on all days when rain did not fall. The weight of nodules per plant varied significantly between sowing dates and showed seasonal trends in both legumes, but in different directions. In P. sativum nodulation was at a minimum at the midsummer sowing date but with P. vulgaris the mid-summer sowing gave maximum nodulation. The data are further analysed in terms of number and size of nodules, and nodule weight as a percentage of plant weight.

The polyphagous nature of the dark-headed rice stem borer, Chilotraea polychrysa (Meyr.), may contribute greatly to its ability to survive periods of food shortage when rice plants are scarce. Investigations on the preference and survival of C. polychrysa on seven selected hosts belonging to the Gramineae revealed that it oviposited on all the hosts tested, but showed a marked preference for its normal host, rice (Oryza sativa). Survival rates on rice and the alternate hosts did not differ significantly. The percentage of larvae surviving to the adult stage was generally low because of the high rate of mortality from larval to pupal stage, irrespective of host species. In rice, there was distinct ovipositional preference for plants at the maximum vegetative stage rather than for younger plants. The larval survival rate increased with the age of the host from 35 to 65 days, but dropped sharply when infestation occurred on plants 80 days old, by which time the inflorescence is beginning to emerge.

The yield and soil data are presented of four long-term experiments on sugarcane at Muzaffarnagar (Uttar Pradesh), Anakapalle (Andhra Pradesh), Padegaon (Maharashtra) and Shahjahanpur (Uttar Pradesh). On soils where phosphorus and potash were not limiting, application of ammonium sulphate over 14 years at Muzaffarnagar and Anakapalle gave higher yields than those obtained by application of farmyard manure, and the fertility status of ammonium sulphate plots was in no way inferior to plots treated with farmyard manure. When phosphorus was also limiting, the application of a basal dose of compost on black cotton soil maintained yield levels. There was a steady decline in yields of cane in plots which received a dressing of ammonium sulphate without any basal dose of compost, but when N.P.K. equivalent to the compost were added the yields were equal to those from plots receiving compost. Thus the effect of compost is explanable on its nutrient content rather than on its effect on physical properties of the soil. In Shahjahanpur there was a decrease in cane yield as the experiment progressed, but the decline in yield in ammonium sulphate treated plots was of the same magnitude as from the plots receiving no dressing of ammonium sulphate. By changing the cane variety and the rotation simultaneously, the yield from all plots went up but subsequently showed a declining tendency.

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.

Leucaena leucocephala (Lam.) de Wit. failed to nodulate with 94 of the 99 strains of Rhizobium tested, representing the seven recognized cross-inoculation groups of nodule bacteria. A group of legumes including L. leucocephala, Mimosa invisa Mart., M. pudica L., Acacia farnesiana (L.) Willd. and Sesbania spp. showed the properties of a cross-inoculation group of plants. Rhizobia isolated from these legumes were all fast-growers and nodulate L. leucocephala, often effectively, and also many other tropical legumes, including Vigna sinensis (L.) Savi ex Hassk., which are usually nodulated effectively with slow-growing root-nodule bacteria. The taxonomic significance of the results is discussed.

A procedure is described in which variation in the attenuation of β-radiation by water held in nylon pads is used to show changes in the water content of soil. The method enables sequential measurements to be made in narrow zones of soil under field conditions; the results are not influenced by the presence of soluble salts.

Cocoa was used as a test crop to compare the use of nine plant species and natural regeneration as ground covers in plantations. The nine species were Tephrosia hookeriana and villosa mixtures, Indigofera sumatrana, Flemingia congesta, Desmodium asperum, Cassia tora, Indigofera spicata, Crotalaria longithyrsa, Mimosa invisa, and Tithonia diversifolia. F. congesta and T. diversifolia gave the best and most persistent ground cover. Significant differences appeared in the effects of the covers on cocoa jorquetting, heights of jorquette, stem diameter and yields. T. diversifolia retarded cocoa development (to as low as 34% of control) while the others appeared to improve it. Yields in plots of Tephrosia mixture, I. sumatrana, and F. congesta were respectively 72, 59 and 54 per cent higher than under natural regeneration.

The percentage dry matter of some Nigerian vegetables increases with age. Corchorus olibrius gave the highest yield of vitamin C after five weeks, but the stage of maturity had less effect with other vegetables. The oxalic acid content of Celosea argentea was very high, approaching a lethal level. It appears that some of the vegetables are best at about six weeks from sowing from the standpoint of eating quality, oxalic acid and vitamin C content.

Fourteen out of 43 fungicides were selected, after laboratory screening, for field trials against coffee berry disease. Each fungicide was compared with a commercial cuprous oxide formulation and an unsprayed control, by assessing conidial production of bearing coffee branches and by recording the percentage of healthy ripe berries picked. In assessments of fungicidal efficiency, healthy ripe berry counts gave more consistent results than those obtained by measuring conidial production. The results from berry counts indicate that in these experiments Ortho Difolatan (BSI ‘Captafol’) was equal, but not significantly superior, to the standard formulation used in estate spraying. The annual rhythm of conidial production seems to have changed over the past five years. The significance of this is discussed in relation to the control of coffee berry disease.

A two-year field investigation was conducted to evaluate the response of two varieties of Guinea grass and two leguminous species, grown alone and in mixtures, to fertilizer treatments. Styloxanthes gracilis and a Guinea grass variety ‘Liconi’ were observed to be superior to others in their yielding ability. Styloxanthes and the Liconi Guinea grass appeared to be mutually compatible at particular seeding rates. Sabi Guinea grass and Centrosema pubescens were the poorest performers under all conditions. Findings also suggested that the adapted and mutually-compatible legumes and grasses could be grown in mixture under tropical conditions, and high yields obtained without the use of expensive nitrogenous fertilizers.

Component analysis was applied to the interpretation of (a) leaf analyses from six similar groundnut fertilizer trials, and (b) the chemical composition of different parts (root, stem and successive leaves) of the sugar cane plant. For each of the groundnut trials it was found that approximately 60 per cent of the total variation in N, P, K, and Ca could be accounted for by two independent linear functions of the elements, representing the balance of N and K with Ca and the balance of N with P and K. The second of these functions was consistently affected by phosphorus applications. Yield was related to one or other function, according to trial, but never to them both. Throughout the sugar cane plant the elements N, P, K, Ca, and Mg were found to be distributed between the roots and the aerial parts, and between active photosynthetic and non-photosynthetic tissues. In both cases the result was a reasonable and consistent simplification of a considerable body of data, such as had not resulted from a series of univariate analyses of variance.

The problems involved in the estimation of potential evaporation in the tropics are discussed, and available methods for calculating potential evaporation are assessed. A computer programme is described which evaluates Penman's formula, accommodating data from the very wide range of conditions experienced in tropical agriculture. The programme conforms with recent W.M.O. recommendations and is written for computers available in many parts of the world. An important component of the programme is a strict data validation procedure. The output includes daily and mean ten-day estimates of E, using the reflection coefficients for open water and for a crop as well as both calculated and, where available, measured values of radiation.

Four standard Nigerian varieties of sorghum were grown in trials together with local varieties representative of sorghums from each of the five main ecological zones. Analysis of the data showed a relation within each zone between mean yield and time of heading. When the standard varieties and the local varieties flowered simultaneously, yields were similar. When the standard varieties flowered later—or in some cases earlier—than the local varieties, the local varieties out-yielded them.