Effects of three levels of N application and four intervals between harvests on field swards of perennial ryegrass (Lolium perenne L.) were studied during 6-week periods in summer and spring. Ryegrass was compared with tall fescue (Festuca arundinacea Schreb.) in spring and autumn.

An increase in the interval between harvests from 1 to 6 weeks allowed a larger, positive response to applied N to develop in respect of dry-matter yield, weight per tiller, and leaf blade and sheath length. Response to N was expressed more in terms of larger leaf blades than in a larger number of tillers. Tall fescue leaf blade size was increased more than that of ryegrass by a period of uninterrupted growth in May.

Within 1 week of its application, N had increased the N content of both emerging and dying leaf blades and had increased the width and reduced the weight per unit area of the emerging blades. The positive effect of N on blade width (and on blade length where uninterrupted growth was allowed) and its negative effect on weight per unit area were ‘carried through’ the sward, to be recorded a second time when that generation of blades had become the dying blades.

Applied N increased the number of tillers, the rate of emergence of new tillers, the proportion of tiller buds which developed into tillers, and the proportion of relatively young tiller buds which developed.

An experiment was conducted over a 2-year period at two sites in the central rainlands of Sudan under rainfed conditions at one location and under supplementary irrigation at the other to investigate the effects of cultivars and spacing on yield and yield components of sunflower. Row spacing had no significant effect on grain yield under either system of production. Under rainfed conditions, the late maturing cultivar Manchurian performed better under wider row spacing than Hungarian-A which is a medium late maturing variety. Size and number of seeds weie significantly affected by row width. It is argued that the choice of a row spacing for sunflower production on a commercial scale in dry regions should be evaluated in association with machine efficiency which is affected by plant height, stem circumference, head diameter and lodging, all of which were significantly affected by row width. Also the number of plants established per unit area of land differed between systems of farming.

Normal and brown midrib-3 (bm3) maize plants of three genotypes (Inra 188, Inra 240 and Inra 258) were sampled at three stages of maturity. Whole crop and plant components were analysed for in vitro digestible organic matter in the dry matter (DOMD) and the concentration of neutral detergent fibre, cellulose, hemicellulose, xylose, soluble sugars, starch and total nitrogen in the dry matter.

The concentrations of total nitrogen, neutral detergent fibre, cellulose, hemicellulose and xylose were similar in both normal and bm3 plants. Xylose was the main constituent sugar of hemicellulose forming 70–75% of the total hemicellulose. The higher concentration of soluble sugars and lower concentration of starch in the bm3 plants was attributed to the later maturity of the bm3 plants.

The bm3 gene significantly reduced lignin synthesis in the whole plant and plant components at all harvests. The mean concentration of lignin in the normal and bm3 plants were 2·2 and 1·4%, respectively. The ferulic and p-coumaric acid concentrations in the bm3 plants were 1·31 and 0·93 mg/g D.M. compared with 1·59 and 1·16 mg/g D.M. for the normal plants, respectively.

The in vitro DOMD values for the bm3 plants were significantly higher (P < 0.05) than their normal counterparts.

An approximate analytical method derived by Wilson & Gelhar (1981) is a powerful and flexible one for calculating solute distribution profiles developing under steady state and transient water flow conditions. Solute concentration profiles developing from an initial deposition in the surface layer, as the soil profile returns to field capacity, have been calculated using the method for idealized representations of the two principal forms of water redistribution.

The profiles depend very strongly on the mode of redistribution of the water. However, the small spread of the final profiles (at field capacity) across the range of water redistribution types examined suggest that, for agricultural application, it might be accurate enough to use a simplified representation of the actual redistribution rather than the correct, and inevitably more complicated, water flows and distribution.

Daily supplements of dried Leucaena leaf meal (500 g/head) were offered for 3 weeks to steers in metabolism cages. The steers had previously been fed diets of oaten chaff (5 kg/head/day) ormclasses and urea (4·5 kg/head/day) with restricted forage (2 kg/head/day). Excretion rates of the primary degradation product of mimosine, 3-hydroxy-4(1H) pyridone (DHP) by steers fed the two diets were compared. These compounds appeared in urine on the 1st day after Leucaena feeding had commenced and output remained fairly constant after 4 days. Mean weekly urinary outputs (g) of DHP from steers fed the oaten chaff or molasses + urea diet were 13·45 and 7·50 respectively. These levels corresponded to 0·23 and 0·13 of the amounts ingested. When steers were fed the molasses + urea diet, DHP continued to appear in urine up to 5 days after Leucaena had been withdrawn from the diet. On the oaten chaff diet no DHP was detected after 3 days following withdrawal of Leucaena.

The effects of casein or formaldehyde-treated casein supplements on the output of urinary DHP by steers fed oaten chaff plus Leucaena was evaluated in a second experiment which ran concurrently. The animals were fed the test diets for 3 weeks before collections were made. Mean DHP outputs (g/day) from animals fed the control diet, control diet plus casein or control diet plus formaldehyde-treated casein were 1·89, 2·21 and 2·44 respectively.

These results confirm substantial degradation of DHP and that the extent of degradation can be affected by the dietary regime in which Leucaena is fed.

is generally used to describe the lactation curve in cattle, where yn (kg) is the average daily milk yield in the nth week of lactation (n = 1, 2, 3, …, N), a is a scale parameter, and b and c are shape parameters. The model was first proposed by Wood (1967) and is widely used in practice to describe the lactation curve for fat, protein, lactose and wholemilk production; it has also been used as a basis of a mathematical model for poultry egg production (McNally, 1971). Having estimated a, b and c by regression analysis, the total lactation yield Y (kg) can then be calculated as

Rapeseed and mustard crops are the second most important source of edible oil after groundnut in India. The average yield of these crops is around 600 kg/ha which has been static for several years. These low yields are of increasing concern in view of the short supply of oil seeds in India. Considerable breeding efforts are being directed to improving production potential as well as stability of yield in these crops (Prakash, 1980). An understanding of the physiological basis of yield formation can be of great help in selecting for high and stable yields. However, there is little information available on the production physiology of these crops (Mehrotra, Saxena & Moosa, 1976; Bhargava & Tomar, 1982).

The production of haploids in large numbers is of great value to plant breeders and geneticists and this has led to the development of new techniques for haploid production (Nitzsche & Wenzel, 1977). In cultivated barley, Hordeum vulgare, there are four principal methods of isolating haploids: the culture of microspores, the isolation of embryos following the interspecific hybridization of Hordeum vulgare with H. bulbosum, ovule culture and the use of the haploid initiator gene (Kasha & Reinbergs, 1982). The present paper focuses attention on the use of the haploid initiator gene (hap) and compares this method with the H. bulbosum and microspore culture methods of haploid production.