Tubers of Dioscorea alata L. cv White Lisbon, affected by Internal Brown Spot (IBS) disease, and stored under ambient conditions on wooden or wire racks, did not show significant increases in IBS incidence and mean lesions over storage periods of up to 18 weeks. Storage under different conditions of temperature (13, 20 and 28 ± 3°C) did not have any significant effect on IBS incidence; but tubers stored under conditions of high relative humidity (95 ± 2%) showed less IBS and greater mean lesion diameters. Although a significant reduction in disease incidence occurred during storage under the latter conditions, the effects of increased lesion size resulted in some deterioration of tuber quality.

Field experiments were conducted for 4 years to study the yield of ‘kharif’ and ‘rabi’ crops grown in sequence on two soils differing in water-holding capacity. The results indicated that drought caused greater reduction in yield of rainy-season crops on loamy sand than on sandy loam soil. In low retentivity soil it was more profitable to raise a single crop of wheat on soil-stored water. In sandy loam soil of higher retentivity, two crops a year gave much higher yields than a single crop. Of the sequences tried, maize followed by wheat gave the highest and most stable yields. For ‘rabi’ crops, stored water showed a better yield response than an equivalent amount of rain during the growing season.

The cyanide contents were determined quantitatively of the peeled roots of 108 cassava clones, which had been previously selected as low-cyanide by the picrate leaf-test, and compared with the qualitative picrate leaf-test scores used for rapid screening. The correlation coefficient between root tuber cyanide content (dry weight basis) and leaf-test score was r = 0·36 (P < 0·01). The picrate leaf-test, while useful for screening large numbers of clones in early stages of breeding, needs augmenting by more accurate methods. There was no significant correlation between root cyanide content and dry root yield (r = 0·18). The cyanide content varied considerably between roots of the same plant; and plants of the same cultivar grown under the same conditions. Possible improvements in the effectiveness of the cyanide screening procedure are discussed.

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.

New productive variants (PV) with physiological and morphological characters distinctly different from their original counterparts (OR) were isolated under disruptive selection in Brassica campestris cv Brown Sarson. Two new breeding approaches were tested—mating (PV × OR) F1 lines with selected cultivars, and mating disruptive with two-directional selection lines. The resulting superior three- and two-way hybrid populations, when advanced through large-scale inter-mating, produced double the yield potential of the existing controls. The genetic principles behind these breeding approaches are discussed.

Differences in the net photosynthetic rates of two classes of Hevea clonal seedlings are explained in terms of resistances to carbon dioxide diffusion from the outside air into the carboxylation sites. The residual resistance, the sum of the mesophyll and the carboxylation resistances, is apparently related to photosynthetic rates.

In a field experiment to estimate water needs of intercropped sorghum and soyabeans, leaf water potential (LWP) and canopy light transmission were measured. Sorghum had 8–11% lower LWP when grown in mixture than alone, but soyabeans, shaded by sorghum had a higher LWP than in monoculture. Absolute LWP values suggest that only about 10% additional water would be required by the mixture compared with individual requirements of the aggressor species in a two-species mixture of this nature.

Grain maize in south-east England showed a markedly flat-topped curvilinear response between density and grain yield, maximum yields being obtained over a range of 80,000–120,000 plants/ha, but yields were reduced at less than 70,000 plants/ha. A general density recommendation of 80,000–90,000 plants/ha is suggested, or a seed rate of 95,000 seeds/ha to allow for germination losses. Yields of cv Anjou 210 and DeKalb 202 showed some decline when the density exceeded 100,000 plants/ha, whereas yields of Pioneer 131 increased above this value and 100,000 plants/ha can hence be recommended. Although planting above the optimum density markedly increased the incidence of stem lodging at harvest, only a minor delay in stage of maturity occurred.

Forage production of common vetch in semi-arid Mediterranean regions can be increased by varietal improvement. Dry matter content and crude protein yield were affected by environment more than crude protein content and harvesting date. Forage produced in environments where plants grew quicker was of lower dry matter content, higher crude protein content but of similar weight as forage produced in late environments. Variations in annual rainfall explained 35 to 76% of the total variation in dry matter yield.

The use of a durometer to assess hardness of onion bulbs is described, and compared with the use of a tensile testing machine. Results from the two tests were closely correlated, and significant varietal differences were detected in bulb hardness by both machines. The durometer is of particular value because of the simplicity and non-destructive nature of the test procedure.

Three procedures for handling missing values in randomized block experiments with more than one observation per plot are examined, and their effects on the resulting expectations of mean squares in the analysis of variance studied. Using the average of the available observations in the plot in which the missing value occurs has the least effect on the validity of the tests of significance and on the estimation of variance components.

In a two-year study the yields and water use of corn were studied under four planting patterns, with different soil moisture regimes and organic (paddy straw) mulches. Normal planting and irrigation resulted in higher yields and lowest water use efficiency, while double file planting in deep furrows (rafter method) gave greatest efficiency of water use but with a slight decrease in grain yield. Mulches improved water use efficiency by 50–60% and reduced irrigation requirements by four to six irrigations. Under limited moisture conditions a combination of these practices is likely to reduce irrigation requirements by half and to double water use efficiency.

A method is described of inducing many ‘eyes’ on yam tubers to sprout, and of using the sprout-bearing segments as propagules for establishing yam fields. The number of such propagules obtainable from a tuber depends on its size, but the method greatly increases the rate of propagation and holds special promise for both breeding and commercial production of yam.

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.

A field experiment to study the response of pop corn (Zea mays Everta) to various levels of nitrogen and plant population was undertaken at the Research Station, Bajaura (HP) during kharif 1974 and 1975. Increases in nitrogen level from 0 to 60 kg N/ha increased grain yield significantly by 54·8%, but yield differences between 60 and 90 kg N/ha were non-significant. Various plant densities did not affect yield significantly. Yield-contributory characters were significantly influenced by treatments and were interrelated with yield under the influence of nitrogen and plant population levels.

Leaf protein concentrate was prepared from the weed Parthenium hysterophorus L. and the nutritional properties of this preparation were studied in relation to its amino acid composition and digestibility. The product and the residual fibre closely resembled similar products made from conventional forage species.

A series of 17 crop-loss assessments was made under simulated farmers' field conditions in the three main rice cropping seasons of Bangladesh. The main insect pests were the rice stem borers (Tryporyza incertulas, Chilo polychrysa, Sesamia inferens) and in the monsoon rice gall midge (Pachydiplosis oryzae). Disease incidence was negligible. In the winter and early monsoon yield losses averaged 4 and 6% respectively, but economic benefit was only derived from insecticide application in the monsoon season, when there was an average yield loss of 16%. An economic threshold of 5–10% damaged tillers (‘deadhearts’ and ‘onion shoots’) was indicated for early attacks of stem borers and gall midge. Possible reasons are given for the usually low incidence of insect pests and diseases in Bangladesh rice.