Effects of cutting lengths on tuber yields and vine production of Missus and Madam sweet potatoes, as influenced by two different fertilizer regimes, were studied on Njala upland soils of Sierra Leone. Cuttings 61 cm. long gave significantly the highest tuber yields for both early-maturing cultivars when fertilized with 336 kg. sulphate of ammonia, 112 kg. basic slag, 448 kg. sulphate of potash, 841 kg. lime and 340 kg. sulphate of magnesium per ha. in two split applications a month apart. Fertilized with 502 kg./ha. sulphate of ammonia per application for 4 applications, 61 cm. long cuttings again gave the highest vine production. The lower the vine/tuber ratio, the higher the tuber yield.

The effects of frequency of potash fertilizer application and of different rates on sweet potato yields were studied in three different cropping systems on Njala upland soils. Fertilizers containing higher K rates (448 kg/ha sulphate of potash) and an N/K ratio of 3:4, gave maximum tuber and low vine yields with low vine/tuber ratios on intensively cropped areas, whereas fertilizers containing lower K rates (112 kg/ha sulphate of potash) and an N/K ratio of 3:1 gave maximum but relatively low tuber and relatively high vine yields, with relatively high vine/tuber ratios on newly cropped areas after seven years bush fallow. Two equal split applications of fertilizer is recommended under the weather conditions prevailing in this part of Sierra Leone.

Effects of Alar on growth, flowering and yield parameters of standard-planted and closely-planted late-bearing okra were studied. Lower concentrations of Alar, applied once 6 weeks after sowing on standard-planted okra, significantly advanced days to first flowering and depressed height at first flowering and final height. Higher Alar concentrations, particularly 2000 ppm applied twice after 3 and 6 weeks on closely-planted okra, produced more, longer and heavier pods, and therefore higher total pod yield in unstopped than in stopped okra, in addition to advancing days to first flowering and depressing height at first flowering and final height. The agronomic practice of stopping okra at 6 weeks reduced pod number, pod weight/plant and total pod yield/ha in unsprayed plants.

The effects of delayed hand weed control at 30-, 45-, 60-, 90-day intervals, and no weeding, on sole-crop cassava, was studied in two experiments on the upland soils of Sierra Leone. Timing and frequency of weeding were important in influencing root number and root yield, and delayed weed control depressed both attributes. The critical period of competition was in the 45-day weeding interval, with six weedings in a 14-month growing period. Rottboellia exaltata was the predominant species amongst the permanent grasses on the no-weeding plots.

An experiment was conducted during the minor season in Sierra Leone to determine the optimum planting date for a photo-insensitive cowpea cultivar and study the relations between total rainfall and soil moisture available at different growth stages. Cowpeas planted in early September produced the tallest plants and higher grain yields than from other planting dates, since they benefited from 90% of the season's rainfall and made use of stored soil moisture. Average weekly rainfall or soil moisture in the top 15 cm of soil, recorded from planting to 50% flowering, can be used to predict cowpea grain yield.

In a 20 plot experiment with central composite second-order rotatable design, basal non-chlorophyllous sections of “D” leaves of Sugarloaf pineapples were sampled at harvest and analysed for N, P, K. Maximum yield of 17·8 tons per acre of good quality Sugarloaf pineapples and maximum fruit length of 27·4 cm. were associated with the nutrient combination of 36–42–32 lb/acre N P K applied at 4, 6, 11 and 12 months. The nutrient levels in the basal sections of “D” leaves corresponding to maximum fruit yield were 0·35–0·40% N; 0·04% P; 0·44% K; K/P 11·2–11·5: 1. K/P ratio for maximum fruit length was 10·4–11·5: 1. N/K ratio was associated with lodging.

Effects of plant population on mean yield and yield components of 2-year sole cassava crops were studied on Njala upland soils of Sierra Leone in two experiments. Increasing plant population of multi-shoot Cocoa cassava over 7000/ha decreased all the parameters studied except top/root weight ratio, which increased. The observed effects were attributed to competition for environmental resources, since area of land/plant unit decreased as plant population increased. The relations between plant populations and yields of fresh root and cortex dry matter were asymptotic, indicating that the respective yields were products of the vegetative phase of cropping.

Effects of fertilizers on harvest time and yield of cowpeas were studied on upland soils in Sierra Leone. In a 25 confounded factorial trial, on soil which had been cropped successively with 2 years of Smooth Cayenne pineapples and 14 months of cassava, the treatments did not affect harvest time significantly, but N, P and NP Mg produced very favourable effects on grain yields. In a randomized complete block experiment on soil previously cropped with two successive cassava crops, there was a significant difference in total yield of dry pods between the control and most treatments.