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.

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.

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.

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.

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.

Competition was studied among four varieties of jute, one cultivated and one wild type of each of C. capsularis and C. olitorius. Varieties exposed to competition showed significant effects on different characters at species and variety level for all the characters. Variety competition, average competition except for base diameter, and specific competition except for node number and base diameter, were significant for all the characters. Wild forms were less effective than cultivated ones as competitors, and the action of one species on the other did not affect all growth parameters in the same way.

Soil acidity, incipient potassium deficiency, and a deficiency of one or more trace elements were limiting factors in three trials of long-term soil fertility changes under continuous cultivation in the Sudan Savanna zone of Nigeria. The effectiveness of organic manures is explained largely or wholly in terms of these factors, since no evidence has yet been found to suggest that the addition of organic matter as such is of value.

Shifting cultivation of dry rice on steep hill-sides continues to be widely practised in Sarawak, Malaysia. Fertilizer experiments have shown that economic increases in yield can be obtained by mixing 0·9 kg. (2 lb) of mono-ammonium phosphate pellets (11 per cent N: 21 per cent P) with 2·4 kg. (5·3 lb) of seed just before dibbling. In certain areas additional increases might be gained by further increasing the rate of application of phosphorus, from the use of potassium, and from top-dressing with nitrogen. Closer spacing (30·5 cm. or 12 in. square) than that traditionally used should also increase yields per unit area.

The quality of bean pods was influenced to a large degree by the variety, season of planting and the precise time of harvesting. The varieties Tenderette, Executive and Bush Blue Lake 274 were outstanding in their concentrated yield and pod quality. The development of seeds in the pods was faster in beans planted during the spring than in the autumn. Thickening of the pods during ripening was more rapid in the autumn than in the spring season. Outstanding differences were found between varieties with regard to the speed of seed development during pod ripening. As opposed to the outstanding differences between varieties with regard to quality characteristics, the differences with regard to yield were generally small and without economic importance.

CCC applied to bread wheat, in 1967 and 1968 as a foliar spray at 1·40 and 2·28 kg./ha. a.i., prevented and/or delayed lodging to some extent. However, this effect was small and complete control of lodging seems to be unlikely, even when using large amounts. CCC increased grain yields, by 1·5 to 10·9 qu./ha., depending on the extent to which lodging was reduced. Significant depressions in yield were obtained, presumably owing to an observed increase incidence in ear diseases, particularly Septoria nodorum. The increase in grain yield was due mainly to an increase in 1000 grain weight and grains per ear, whereas the effect on tillers per unit area was slightly negative. Where no lodging occurred, there was a slight but non-significant tendency for increasing grain yields after CCC treatment.

The literature for the past seventy years describes a variety of methods of sampling tea leaves, in some of which analytical data from samples have been suggested as capable of widespread use as a measure of the nutritional status of tea plantations.