The dependence of yields of sweet clover and alfalfa on environmental conditions, including soil acidity, at the germination stage has been studied over a period of 28 years. Results have been dramatic: sweet clover and alfalfa can grow well and produce large yields even on strongly acid soils (pHKCl 4.0) providing that the process of germination starts in a neutral medium.

An experiment is described on the establishment of cocoa on clear-felled land, using various ground covers on which 22 NP:KMg factorial treatments were later superimposed. Growth of cocoa was improved in mulched and clean-weeded plots and the unshaded trees began bearing two years after planting, which is exceptionally early for young cocoa in Ghana. In the third year responses to NP fertilizer were obtained and in the following year yields were very high, up to 2170 pounds dry cocoa per acre. This was partly responsible for K deficiency, particularly in plots without mulch and KMg, which led to declining yields especially on the NP plots. Significant increases were thence obtained from the KMg fertilized plots. Mulching at the rates used in this experiment is too expensive and uneconomic, but K fertilizer applied at rates higher than the present rate of 75 lb K2O/acre/annum may be needed on Ghanaian forest soils if they are clear-felled for growing unshaded cocoa.

In short clonal rows of sugarcane the mean weight of adjacent rows contributed significantly to the variance of row weight, mainly because some clones could increase their cane number at the expense of slow-tillering clones. Weight per cane and sugar content were unaffected by competition. Significant correlations were found between sugar content and (a) the rate of leaf appearance, (b) the ratio of fresh weight of leaf blade to fresh weight of joint, and (c) fibre as a percentage of cane fresh weight.

Formulae are given to calculate the efficiency of the split-plot design, in which whole-plot treatments are arranged in randomized complete blocks. Efficiency for each of the whole-plot and split-plot treatment comparisons is discussed relative to three simpler designs. Tables are given to facilitate calculations for experiments in which up to five whole-plot treatments and five split-plot treatments are tested, using four, six or eight blocks.

Forty-six cultivars of linseed oil (Linum usitatissimum L.) were grown under wet and dry season conditions in the Sudan Savanna of Nigeria. Only during the dry season was production good and cv Dunes consistently outyielded all other cultivars in terms of seed and oil content. Trials of sowing dates gave maximum seed yield and oil content from plots sown during late October. In row spacing trials, rows 15–22 cm apart and seed rates of 58–78 kg/ha were found to be the most practicable. There was a linear relation between increasing rates of nitrogen and seed yield, maximum production being obtained at 55–88 kg N/ha, but oil content was slightly depressed at levels above 33 kg N/ha.

Hand-planted plots of across-row-oriented corn seeds (Zeamays L.) produce highly structured leaf canopies and have shown significant yield advantage over randomly planted plots in prior studies. For further investigation of the phenomenon by simulation, the objective of this study was to develop a probabilistic model for the correlation between seed orientation and initial plant orientation. In greenhouse trials, the azimuthal orientation of kernels of four different hybrids was recorded at planting. At collar setting of the seed leaf, the orientation of the seed leaf was determined and the angular data subjected to the analytical methods of circular statistics. The results indicate that the correlation between seed azimuth and seed leaf azimuth can be described by a von Mises distribution. The probabilistic seed to seed leaf azimuth model described herein may be implemented in simulation models to investigate the effect of canopy architecture, canopy closure and light interception efficiency of corn under conditions of seed oriented planting.

Forty-one factorial experiments on rates and forms of the three major elements and rates of some minor and trace elements were carried out over the period 1954–1962 in Iringa, as part of a project to introduce Virginian-type tobacco varieties into the area. There were major responses to nitrogen and phosphate, and a close relationship between their effects, but no responses to other elements. Nitrogen raised yield, particularly in wet seasons, but generally tended to reduce quality, severely above 44 lb N per acre and at lower levels in dry years. Phosphate raised yield and quality, and in some instances crop failures occurred in its absence. Data suggested the optimal N : P2O5 ratio in fertilizer mixtures to be 1 : 15. Despite lack of response to potassium a small amount was recommended, to cover requirements for leaf characteristics which were not measured. The programme amply succeeded in its aim of establishing ‘average’ fertilizer recommendations, which were fundamentally sound, for the whole of the Iringa tobacco growing area. These recommendations are summarized.

Although several studies have underlined the advantages of using insect-proof nets to improve yields while reducing the use of pesticides, one obstacle to the diffusion of this technique in tropical conditions is the associated increase in temperature in the tunnel. The aim of this work was to assess the interest of combining the physical protection provided by nets against insect pests with the beneficial impacts of using shade nets to grow cabbages. A two-season experiment was set up to compare temperature conditions, insect pest populations, yields, and the quality of cabbage crops grown in the open field and in low tunnels covered with nets providing different degrees of shading, 17.2% by white and 50.1% by silver nets. During the day, the temperature under the white and silver nets was 10.4 °C and 6.3 °C higher, respectively, than in the open field in the first season, and 6.5 °C and 5.9 °C higher in the second season. Both insect-proof nets significantly reduced insect pest populations and hence the need for insecticide treatments. The white nets increased marketable yield by 45.4% in the first season and by 16.4% in the second compared to yields in the open field, whereas silver nets reduced yield by 18.6% and 15.0%, respectively. The reduction in yield under silver nets was attributed to excessive shading that prevented the light requirements of cabbage crops from being fulfilled. Economic analysis raised some concerns about the profitability of the use of netting to grow cabbage due to investment costs and the lack of premium prices for vegetables produced with fewer pesticides in local markets.

Examples are taken from three biometrical texts, two unpublished experiments and Yates (1937) to illustrate quantitatively how the lay-out of the plots can affect the estimate of error variance in field experiments and how confounding of treatment and positional effects can arise. In two examples in which the plots did not run the whole length or width of the block, the estimates of error were reduced by one half and one quarter respectively by allowing for sub-blocks within blocks or for rows and columns. In split-plot experiments where the main plots were split breadthwise, the sub-plot error was about the same size as the main-plot error or larger whereas it is expected to be at most one third that of the main plots when these are split lengthwise. Serious bias can arise in the estimate of treatment effects due to confounding with positional effects; this is illustrated.

The mass selection reservoir (MSR) is one way to take a population approach to the breeding of sugarcane. Yield data from four successive plantings of a sugarcane MSR showed consistent superiority to a commercial clone. The problem of defining satisfactory selection indices for the MSR is discussed.

Soil samples from Guneid Sugarcane Scheme, representing high- and poor-yielding sites, were collected and analysed. Yields of sugarcane were significantly and positively correlated with exchangeable potassium and clay content (P = 0·01), whereas there was a negative correlation between yield and exchangeable sodium percentage (P = 0·05). Multiple regression on soil clay content, exchangeable potassium and ESP accounted for 48·1% of the observed variability of yield of sugarcane, indicating that the clay content was the most important soil factor determining yield of sugarcane in this area.

The diffusion of rice varieties introduced into an area with poor production potential and problems of soil degradation was studied in a farming systems research and extension programme. Two rice varieties, BW. 272–3 and At. 85–1 were identified as appropriate for the area and efforts made to transfer the experimental results to the farmers. BW. 272–3 was widely adopted by farmers in the lower, intermediate and upper areas of the recommendation domain but adoption of At. 85–1 was confined to the intermediate and upper areas. Adoption of rice varieties was mainly governed by the characteristics that allowed a variety to perform well under adverse conditions and by the farm gate price it could command, which depended on grain pericarp colour.

Difusión de nuevas variedades de arroz