For Muguga, in Kenya, confidence limits of expected ‘twenty-day’ rainfall may be reliably derived through a logarithmic transformation of the skew rainfall data. Frequency distributions of rainfall totals received during specific crop-growing seasons are examined for three widely separated Kenya sites. It is shown that confidence limits for such seasonal rainfall cannot be obtained by summation of the corresponding limits for the successive twenty-day intervals included within the season. Twenty-day limits should not therefore be accumulated in seasonal comparisons of crop water requirements and precipitation. Such assessments of agricultural site potential must take account of the year-to-year variability of precipitation, but are best undertaken with actual rainfall amounts.

Cultural standards and the husbandry techniques used on small farmers' fields are seldom the same as those practised on research and experimental Stations in the developing countries. The need for extensive agronomic experiments to be sited on small farmers' fields is emphasized. This method has been quite widely used with annual crops, but could with advantage be more generally adopted in perennial crops. Some of the advantages of this approach in agronomic investigations are illustrated by examples from work carried out in East Africa.

Problems of potato culture are discussed with respect to photosensitivity, seed stock degeneration, and the maturity behaviour of varieties bred in the temperate world. Varieties adapted to temperate climates, when grown under sub-tropical conditions, matured earlier and yielded less than when grown under temperate conditions. The complex problems involved in combining several desirable attributes in a variety are discussed in the light of current breeding procedures and new approaches to solve several of the problems are indicated. Data on the bionomics of aphid vectors of potato viruses suggest methods for maintaining high health standards in breeders' stocks. Techniques are discussed for raising large populations of seedlings from true seeds under sub-tropical conditions.

N and P fertilizers applied to maize had considerable effects over a five-year period, especially when both were given. Initial applications of 47 lb/acre/P2O5 with annual dressings of 58 lb N, produced a mean yield increase of 55 per cent above the control. K gave little response in the first three years, but thereafter became more important. 1120 lb ammonium sulphate nitrate caused striking reductions in soil pH, Ca, Mg, K, total and organic P but increases in exch. Mn and soluble P. 112 lb double superphosphate increased the total and organic P and 65 lb K2O reduced organic P. Organic carbon suffered a mean loss of 33 per cent over five years. Recommendations are made regarding P2O5, N and K on this soil.

Confidence limits of expected twenty-day rainfall have been computed for two widely separated maize-producing regions in Kenya. The 35-km. square survey areas were quite different topographically, and limits were derived for seven rainfall sites in each. Ratios of these limits to the corresponding long-term mean precipitations were evaluated for each site for each twenty-day period during the appropriate maize-growing seasons. For a particular period and confidence level, these ratios were almost constant for either group of seven sites. The variability computed for a single, well-chosen site is therefore representative of quite a large neighbourhood. Expected rainfall totals were also derived for a ‘fictitious’ site, simulating the average precipitation over the whole of the flatter of the two areas. The resulting limits were less extreme than those of any individual site, indicating that areal rainfall, as used in hydrology, is less variable than the agriculturally-important point rainfall.

Effects of N, P and K on yields of cotton were investigated using data obtained over an 18-year period from a factorial experiment comparing various combinations of the three nutrients. The results clearly indicated a significant and fairly consistent response of cotton to the application of fertilizer nitrogen, but the rate of increase in yield with increased N gradually diminished. The response to P was erratic and to K was negligible. The response to N did not vary with levels of P or K. Whether lack of response to P on the alkaline soils of the Gezira was due to sufficient already available in the soil, or because the added fertilizer was fixed and rendered unavailable to the plant needs further investigation. Lack of response to added K was attributed to the high content of available K already in the Gezira soil.

Total and partial correlations are presented between foliar nutrients in a uniformity trial. The method of principal component analysis is applied to the correlation matrices, comparing values for three fronds (3, g and 17). The results are also compared with values obtained elsewhere, and the use of principal components in relating yield to foliar composition is illustrated.

Nodule and plant dry weight of five photoperiodically different cowpea varieties increased with increasing day-length. There were no effective nodules on any varieties in 8-hour days and the response of nodulation to day-length was greater than plant dry weight. Nodule and plant dry weight also increased with increasing availability of water, but at the highest watering rate nodule weight was significantly lower under long than short days. Cowpea should nodulate well under tropical day-lengths provided enough water is available.

Visual symptoms of deficiencies of nitrogen, phosphorus, potassium, calcium, magnesium, sulphur and boron on pyrethrum are described, and compared with those observed previously on other species of chrysanthemum.

Yields of sugar cane in low-silicon soils were significantly increased by the application of both calcium silicate and coral sand. Over and above the significant response to Ca and increase in soil pH, there was a highly significant response to Si. The overall response to the higher level of calcium silicate application (14·2 tons/ha.) over the control was 28·3 tons of cane per hectare. Neither calcium silicate nor coral sand influenced the sucrose content of the juice.

A method of estimating crop production potential was devised and tested in a number of contrasting solar radiation climates. With increasing levels of solar radiation, total dry matter yields of kale, maize and sugar beet increased, whilst energy conversion efficiency declined in kale and sugar beet but increased in maize. Maximum potential crop yields in almost all environments were achieved with a conversion efficiency of approximately 2 per cent of total radiant energy.

Poor emergence of crops is common during the rainy season on the clay soils of the central Sudan. Arachis hypogaea, Sesamum indicum, Hibiscus cannabinus and Gossypium hirsutum were studied under a range of soil water and air-filled pore space conditions by sowing on earth ramps; these were covered with water which was subsequently drained either completely or so as to leave water standing. Air-filled pore space was estimated by air-picnometer and water content by oven drying. The conditions in the sloping beds were related to those normally found in experimental plots (using Triticum aestivum). When the effective air-filled pore space was as low as 10 per cent all crops emerged poorly. Sesame emerged well at 40 per cent and all others at 20 per cent. The best emergence was found when water was drained completely at the shortest interval included in the experiments, i.e. on the day after covering the beds.

In 90 local sesame types there was some association between seed coat colour and seed size, stem height, number of branches, number of pods, yield per plant and earliness. Forty-five coefficients show the degree of correlation between ten agronomic characters. Yield was significantly and positively correlated with all characters except the number of days to first flowering and to first maturity. Stem height, number of pods per plant and seed size seem to be the best criteria for selection in sesame.

Winter wheat seeds were grown on compressed soil (a) with and without smearing, (b) with surface horizontal or at 45°, and (c) with and without a sand cover. Germination was not affected. At a soil suction of 0·1 bar, root penetration of the horizontal surface was decreased by smearing and by absence of an overburden; on a surface of 45° smearing had very little effect. As a general summary of the limited information, root penetration is decreased by 50 per cent for a ten-fold increase in suction above 0·1 bar; the effect of smearing is equivalent to a five-fold increase; and the effect of slope is equivalent to a four-fold decrease.

Application of nitrogen (160 and 80 kg. N/ha.) and phosphate (80 and 40 kg. P2O5/ha.) increased the diameter and height of cane and number of shoots per metre of row, and consequently the yield of minable canes, with significant differences between the effects of the two levels of each nutrient. Potash did not affect the growth and yield of sugarcane. Application of 80 kg. P2O5/ha. was beneficial only with 160 kg. N/ha. but 40 kg. P2O5 proved effective with both 160 and 80 kg. N. because yield of millable cane with 80 kg. each of N and P2O5 was significantly lower than with 80 kg. N + 40 kg. P2O5.

A crop of broad beans was subjected to different water treatments with a view to finding the most economical irrigation policy. Increments in yield were obtained from the sixth to ninth irrigation, but the relative significance of each irrigation after the sixth was dependent upon whether irrigation water was saved during the vegetative and early flowering phase, or during the phase of pod development. The influence of the different water regimes on yield components and on some attributes of growth was studied.

Initial and residual effects of phosphorus, lime and potassium were studied on Natal Common and Dodoma Bold groundnuts. Double superphosphate (D.S.P., 42% P2O5) considerably increased yields of the first two crops. Lime was noticeably beneficial on Dodoma Bold but less so on Natal Common, while K depressed yields of both when applied without P. The LPK treatment yielded best with each variety, but initially P alone was most economic. Comparing D.S.P., Tororo superphosphate (T.S.P., 21% P2O5, 13% S) and Minjingu phosphate (M.P., 15% citric soluble P2O5), T.S.P. gave the best response (625 lb/acre over 3 years), more than double that of equivalent P2O5 as D.S.P. T.S.P.'s superiority is attributed mainly to its sulphur content. Though initially inferior, M.P. proved as good as D.S.P. over 3 years. 224 lb/acre T.S.P. in alter-nate years is recommended. After two or three crops, light applications of lime and potassium together would be beneficial.

In Queensland it is standard practice to burn sugar cane before harvest, but incomplete burns are common, due to the lush condition of the crop and the occurrence of weeds. Experiments conducted over seven seasons to dry out foliage of both weeds and cane, using bipyridylium desiccants, showed that paraquat was consistently more effective than diquat. After treatment of cane foliage, several days were necessary for fully effective desiccation, during which time a slight drop in sugar content could usually be detected. It is practical to spray cane leaves in the outside rows, adjacent to headlands (where weeds normally thrive). Treatment of this peripheral zone could affect no more than 10 per cent of a cane stand, and any loss of sugar would usually be more than offset by the benefits of desiccation, viz: a cleaner burn, quicker cutting, less trash, and fewer penalties.

A uniformity trial was carried out at Banting, Selangor in West Malaysia to estimate optimal sampling rates for determining foliar nutrient contents of oil palms. The results suggest that the unit for sampling in this area is greater than 10 acres but less than 50. A comparison of the results with those obtained in Nigeria shows a large measure of agreement. Factors concerned in choosing a sampling rate are discussed. With the information available a rate of 2–3 per cent appears adequate.

Cocoa leaves were analysed for potassium, calcium, magnesium, manganese, iron, copper and zinc to assess the nutritional status of this crop in Papua–New Guinea, as part of a study into a dieback disease. Potassium and manganese contents of the leaves were generally high, whilst magnesium, iron and copper were often low. Some exchangeable cation data from soils is presented. Nutrient imbalances, toxicities and deficiencies, may make cocoa more susceptible to dieback.