The neutron method of estimating soil moisture content in the field has the advantage that once access tubes are installed no further disturbance to the site is necessary and readings can be taken repeatedly throughout the soil profile at a fraction of the time necessary for the gravitational method. However, measurement of moisture content in the surface layer of soil, the top 10 cm, has proved difficult since the source and detector must be at a depth less than the sphere of influence allowing some neutrons to escape to the atmosphere. This air-soil interface effect can lead to an underestimation of moisture content which is greatest in wet soil (Van Bavel, Hood & Underwood, 1954).

In anaerobic glyoolysis lactic dehydrogenase (LDH) is the terminative enzyme in the sequence of reactions that promote the breakdown of sugars to lactate. The LDH activity of cattle semen and seminal plasma together with its relationship with various characteristics of semen have been reported (Stallcup & Hayden, 1960; Roussel & Stallcup, 1965). Such work in respect of buffalo semen is not available, although there are some reports on LDH activity of spermatozoa and seminal plasma (Singh & Sadhu, 1972; Chauhan & Srivastava, 1973). The present investigation was undertaken to determine the LDH activity of buffalo whole semen as well as of seminal plasma and to find correlations with some physical characteristics of semen.

Studies were made on detopped sunflower plants to see whether the depolarizing effect of NH4 on the trans-root potential is the result of increasing H2PO4 uptake and to determine the effect of NH4 on the flux of NO3 and SO4 in xylem exudate. Increasing the NH4 in the medium increased the H2PO4 flux in the exudate, but decreased NO3 and SO4 fluxes. Ammonium and NO3 influenced the uptake of each other but NH4 had the greater effect. These NH4 effects were attributed wholly or in part to blockage of the root metabolism which may have affected the permeability of root cell membranes. Therefore, the stimulation of H2PO4 flux by NH4 was probably not attributable to any specific effect of NH4 on H2PO4 uptake. Enhanced H2PO4 and decreased uptake of NO3 and SO4 reflects toxic effects of NH4 on the root metabolism.

Vicia faba, in common with other grain legumes, rarely gives economic yield increases in response to soil application of nitrogenous fertilizer either before sowing or at flowering (McEwen, 1970a, b; Day, Roughley & Witty, 1979). The lack of response was attributed to poor uptake of the applied fertilizer particularly at flowering (Day et al. 1979). Garcia & Hanway (1976), however, increased the yield of soya beans from 3695 to 5225 kg/ha with foliar sprays containing N as urea, P, K and S applied during the seed-filling period. Day et al. (1979) using four foliar sprays of the same composition increased yield of V. faba by 361 kg/ha (8·6%) following the uptake of 15% of the 80 kg N/ha applied. However, Robertson, Hinson & Hammond (1977) reported no yield responses of soya beans with up to five foliar sprays of the same composition and noted that those containing ammonium polyphosphate and KNO3 caused leaf damage that significantly reduced yield.

In the assessment of the nutritive value of feeds for animals, measurement of digestibility has been a basic index since 1860 (Schneider & Flatt, 1965). In this laboratory, measurements of digestibility and voluntary feed consumption using sheep have been the basis of feed evaluation procedures for over 20 years (e.g. Milford, 1960). The plants with which our group is concerned, however, are mainly grazed by cattle, and it is important to establish the degree to which extrapolation of results from sheep to cattle is justified for tropical pasture species. Many comparisons between sheep and cattle in terms of digestibility of dry matter and other aspects of feed utilization have been made using temperate pasture species hays, silages, grains and mixed rations; this area has been thoroughly reviewed by Schneider & Flatt (1965). Very few such studies have been made using tropical species, and most of those in Australia have involved the native species Heteropogon contortus (Siebert & Kennedy, 1972) or mixed H. contortus and Bothriochloa decipiens (Playne, 1978), providing material of low quality, containing less than 1% nitrogen. Playne (1970) used one introduced tropical species, buffel grass (Cenchrus ciliaris), and in that work only one of three harvests contained over 1% nitrogen. In the present work three introduced tropical species have been examined, covering a wider range of quality than has been reported previously.

Seed potatoes are grown on the high plateaux of northern Israel where it is cool enough for a summer crop. The seed are used for winter production of ware potatoes in southern Israel. Irrigation is essential because of the arid summers. It is customary to apply much of the N fertilizer through the irrigation system in numerous small doses. Total N rates have ranged between 300 and 400 kg/ha. In 1975 various aspects of N, P, K fertilization for seed potato (Solanum tuberosum L., var. Up-To-Date) production were examined. There were no responses to P or K fertilizers so only the N fertilizer responses are reported here.

Alternaria blight of sunflower caused by Alternaria helianthi (Hansf.) Tubaki and Nishihara is the most important disease of monsoon-grown sunflower crops in India (Kolte & Mukhopadhyay, 1973; Narain & Saksena, 1973). It is also reported to occur in Rumania (Hulea, Iliescu & Bunescu, 1975), Tanzania (Allen, 1974) and Brazil (Ribeiro et al. 1975). The present studies were carried out to assess the effect of different disease intensities on yield and oil content of the sunflower crop.

There are few reports on hyaluronidase activity (Kaur, Chaudhary & Anand, 1976) which is one of the important enzymes concerned with fertilization (Austin, 1960) and to the best of our knowledge none on the relation of hyaluronidase activity to fertility. This communication attempts to study the relation of hyaluronidase activity with various physical characteristics and fertility in buffalo (Murrah) and cattle (HRS) semen.

A large number of flower buds, flowers and premature bolls of cotton are shed without contributing to seed-cotton yield. Abscission may be affected by environmental factors. It may, therefore, be possible to reduce it by modifying the micro-environment within the crop canopy.

Further exploitation of the increasingly popular oil-seed rape crop, Brassica napus L., as a valuable break in cereal production in the U.K., is threatened by the susceptibility of the crop to a number of diseases of which the most serious is likely to be stem canker caused by Phoma lingam (Tode ex Fr. Desm.), perfect stage Leptosphaeria maculans (Desm.) Ces et de Not. (Gladders, 1977; Hewitt, 1977). This pathogen has already severely restricted the cultivation of oil-seed rape in France (Lacoste et al. 1969) and in Australia (Bokor et al. 1975; McGee & Emmett, 1977).