At doses of 75 mg./kg. given per os, Neguvon was ineffective against Sarcoples scabiei var. Auchenidae. Benzene hexachloride (BHC) per os was ineffective at doses of 20 mg./kg. and killed alpacas when the dose was increased. Spraying the lesions with BHC killed the acari and lesions quickly disappeared. Psoroptes communis, the cause of otitis in alpacas, was equally susceptible to spraying. Lesions and their location are described and attention is drawn to the possible role of acari in nostrils and perinea in the epidemiology of the disease. Dipping is, at present, the only method of cure worth using, but the search for systemic acaricides should be continued.

Results are reported from experiments with nitrogen and potash fertilizers in irrigated Rhodes grass (Chloris gayana), into which annual winter legumes, e.g. berseem (Trifolium alexandrinum) and vetch (Vicia sativa) were overseeded. The experiments were carried out over a three year period on a sandy loam soil at Bet Dagan Experimental Farm, Israel. Ammonium sulphate, applied in equal split rates of up to 384 lb N per acre, linearly increased dry matter yields of Rhodes grass, and the increase of yield proportionally increased the uptake of K by harvest. The K content of the dry matter decreased with increasing nitrogen fertilization to 0·47 per cent which, however, was still found sufficient for maintaining maximum production of Rhodes grass. The yield of annual winter legumes decreased proportionally to the amount of nitrogen fertilizer applied during the summer. Acute potassium starvation was observed. An autumn application of potassium chloride restored dry matter production to normal levels. Availability of soil K, expressed in terms of energies of replacement [ΔF(− 1)], decreased proportionally to the amount of nitrogen fertilizer applied. When ΔF reached approximately 4,250 cal/mol, overseeded legumes were K-deficient, whereas Rhodes grass at that value was still able to extinct sufficient K from the soil for normal growth.

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.

Where ancient agricultural sites are brought back into cultivation, using new forms of irrigation, cotton often grows badly in the first few seasons. A theory is developed to account for these failures, and it is shown that heavy irrigations before planting not only produce better crops but may also economise in water.

A breeding programme involving the progeny testing of small East African Zebu cattle for improved growth rates is described and an assessment made of environmental and genetic improvements which have occurred over a ten-year period. Evidence is presented to justify continuing the programme, but suggestions are made to modify it in order to speed up the testing period and also to make more use of genetically superior stock.

Response to potassium fertilization was tested, over a two-year period, in 24 experimental fields, predominantly in coarse-textured soils. Only two fields showed significant yield increases. Potassium availability was estimated on the basis of (a) the free energy (ΔF) of potassium exchange for calcium and magnesium, (b) the proportion of potassium in total exchangeable cations, and (c) soluble potassium extraction in correlation with the potassium content of the plants. Woodruff's method (ΔF) yielded the best agreement (correlation coefficient r = 0·77). ΔF values showed a sufficient supply of available potassium, which may have accounted for the lack of response to fertilization.

An investigation was carried out in 1964 to determine the effect of seed size on oil content and seedling emergence in safflower (Carthamus tinctorius L.). Small, medium and large seeds yielded 37·0, 36·6 and 35·7 per cent oil respectively, and this inverse relationship between seed size and oil percentage (r = −0·9635) was attributed to the increase in proportion of hull in large seeds. In a pot experiment, plants from large seeds emerged earlier than those from small seeds when sown at both 1 and 3 inches depth. Further, plants from large seeds had greater dry weights and leaf areas than the others. The same sort of correlation was also obtained between seed size and early emergence in a field experiment using small, medium and large seeds.

Large scale destruction of mature mandarin orange groves due to root rot has occurred in Central Malaya. During the course of an investigation on the aetiology of this malady, Phytophthora nicotianae var. parasitica (Dast.) Waterhouse was isolated, and a test on the susceptibility of nine common citrus species to Phytophthora root rot was carried out by a modified water-culture inoculation technique. This appears to be an efficient and rapid screening method suitable for tropical conditions. The results showed that none of the species tested was resistant, although the degree of susceptibility varied significantly among species and between groups of species.

The apparent success of overdrilling in improving poor grazing pasture in other temperate climates led to an investigation of the technique under British conditions. With the development of a suitable machine, both for controlling competition and for drilling seeds and fertilizers simultaneously into established pasture, field trials were initiated in 1961 and 1962. Despite the achievement of satisfactory furrows for germination, the subsequent emergence and establishment of improved grasses and white clover was poor. This was thought to be due to various factors, particularly to competition from the short vigorous lowland swards, but also to unsatisfactory furrow environments where difficulties were experienced in covering seeds adequately, and in protecting seedlings from desiccation. Even when an overall application of herbicide was used to control competition, the seedlings were slow to colonize the bare ground and appeared to be particularly vulnerable to desiccation where vegetation was absent. Under the conditions of sward and climate at Aberystwyth, overdrilling by itself appears to offer no promise as a means of grassland improvement.

Although all methods of planning for the maximization of farm profits require knowledge of the basic ‘input-input’ and ‘input-output’ relationships, particularly detailed information is required when using linear programming. Specially designed crop experiments are one major source of such information, but it is important that each experiment should include all major interacting variables, since the response curves estimated from the data, and the relationships extracted from these curves, will otherwise be of little use for determining economic optimum input combinations. Where the matter of interest is the most likely production response, under the planning conditions envisaged, the best available estimate will usually be the average response estimated from a sample of experiments distributed randomly within the conditions. In each experiment of such a sample, the variables being examined should be at the same series of input levels, whilst other variables which are not of interest, but can be controlled, should be held constant at the same general level. With respect to the design of experiments established to generate production relationships, complete factorial and composite or rotatable arrangements are considered to be most suitable, although each of the types has certain disadvantages. Regarding the derivation of ‘input-input’ and ‘input-output’ relationships from the response curve fitted to the data obtained from such experiments, it is felt that this curve should first be ‘scaled down’, to allow both for the more favourable experimental conditions and for losses between the field and the point of use. After this, a number of individual production relationships should be selected, on that portion of the curve expected to be of economic interest. The relationships can then be employed in a linear programming procedure designed to generate a farm plan incorporating that combination of enterprises likely to earn the maximum profit.