In tubers of ten potato varieties the incidence of internal rust spot lesions increased and the calcium concentration decreased when the concentration of calcium chloride supplied to the plants fell from 9 to 1 mM. A simple linear model relating the probit transformation of internal rust spot incidence to tuber calcium concentration for each variety showed that there were substantial differences in varietal susceptibility to internal rust spot which were not related to tuber calcium concentration.

A study was made in the unusually dry 1975–6 season of the distribution of extractable phosphorus and potassium, and of roots, in the top soil in the second year of direct drilling on a Denchworth series clay (with winter wheat), and in the fourth consecutive year of direct drilling on an Evesham series clay (with spring barley). With both soils there were greater accumulations of phosphorus and potassium in the upper 5 cm with direct drilling compared with ploughing. In the Denchworth soil there were smaller concentrations of phosphorus at all depths below 5 cm with direct drilling and in the Evesham soil this depleted zone was located between 10 and 15 cm depth. There was little extractable phosphorus at depths below 20–30 cm.

Measurements of the overall change in concentration of extractable nutrients at each depth between the beginning and end of the season suggested that there may have been contrasting patterns of depletion with cultivation treatments. Depletion was greater between 2·5 and 5·0 cm with direct drilling, and for spring barley on Evesham soil this coincided with the zone in which roots were most abundant. For potassium, there was an increase in the concentration in the 0–2·5 cm zone, apparently due to potassium loss from the maturing crops. At harvest, the total depletion of phosphorus from all zones between 0 and 50 cm depth was appreciably less than data (Cannell & Graham, 1979) on the content of phosphorus in the crop per unit land area, indicating that release from non-extractable reserves in the soil had occurred.

Despite the exceptionally dry summer of 1976, crop growth and yield were not adversely affected by the tendency for extractable phosphorus and potassium, as well as roots, to concentrate in the upper layers where desiccation could occur most readily. Possible reasons for this, as well as factors that may contribute to the observed patterns of distribution of nutrients and roots, are discussed.

The regrowth of Aberystwyth S. 23 perennial ryegrass, S. 24 perennial ryegrass, S. 59 red fescue and S. 170 tall fescue was studied in field swards, comparing four levels of applied nitrogen, for 8 weeks following a clearing cut. The clearing cuts were in mid-October, mid-February and mid-March in each of 3 years, different plots being used on each occasion.

Grass yield was more closely related to solar radiation receipt than to temperature. When radiation during the 3 or 4 weeks before a period of study was added to radiation during the 8-week period, to incorporate some allowance for temperature, the amount of additional yield per unit of additional radiation comparing the first spring period with the autumn period was about the same as that comparing the second with the first spring period. Where no N was applied, there was little or no increase in yield above ground level or above 4 cm from week 1 to about week 6 in the autumn and first spring period, whereas where N was applied yield increased steadily, though rather slowly, during those 5-week periods. Response to N, measured as kg dry matter above 4 cm/kg N applied, was about twice as great in the second as in the first spring period; on the other hand response to N measured as number of days saved in reaching a given yield was greater in the first than the second spring period. The positive effect of applied N on relative growth rate occurred mainly in the rather early stages of regrowth, which seems to be typical of any time of year.

Applied N increased the N and nitrate-N content of herbage and reduced the watersoluble carbohydrate content. Applied N increased the number of tillers and the proportion of yield above 4 cm. Yield below 4 cm was not much affected by N or by stage of regrowth. The ‘earliness’ in spring of S. 24, S. 59 and S. 170 compared with S. 23 was associated with greater height and a higher proportion of yield above 4 cm and not with higher above-ground yield. The ryegrasses responded more to N than the fescues in respect of yield above 4 cm and number of tillers. In 2 years in which the number of tillers was relatively low at the beginning of the spring periods of study, the number increased during those periods and there was a large positive effect of applied N, whereas, in a year in which the number was high initially, there was no increase during the periods of study and little response to N.

The regrowth of Aberystwyth S. 23 perennial ryegrass, S. 24 perennial ryegrass, S. 59 red fescue and S. 170 tall fescue was studied in field swards, comparing four levels of applied nitrogen, for 8 weeks following a clearing cut. The clearing cuts were in mid-October, mid-February and mid-March in each of 3 years, different plots being used on each occasion.

The application of N increased the number of leaf primordia, the number of un-emerged leaves, the rate of leaf emergence and death, leaf blade length, width and weight, sheath length, number of leaves per unit area of ground and proportion of green tissue in total yield. The application of N had little effect on the number of leaves per tiller and tended to reduce weight per unit area of leaf blade. The increase in size, weight and number of leaf blades appeared to be major reasons for the positive effect of applied N on yield, previously reported; and the increase in sheath length contributed to the increase in proportion of yield above 4 cm. Rate of leaf extension was not closely related to yield and was more sensitive to temperature than was yield. Changes during regrowth in blade and sheath length helped to explain changes in weight per tiller, previously reported. The effects of improving weather conditions in late winter/early spring were similar to the effects of applied N: larger, heavier leaf blades, longer sheaths, a taller canopy, a lower proportion of dead material, younger leaves. The length of shoot apex per leaf primordium was relatively constant. Leaves continued to emerge, at a slow rate, in the period December–February. S. 170 had the biggest leaves, particularly in May, and the slowest rate of leaf turnover. Rate of leaf extension was increased by applied N more, on average, in the ryegrasses than in the fescues.

This experiment was made to determine the possible reason for deficiency symptoms seen on fenugreek (Trigonella foenum-graecum) in field trials during the dry summer of 1976. Using rockwool cubes for root support, it was shown that symptoms seen in the field plants resulted from boron deficiency.

The symptoms of boron deficiency in fenugreek are described and illustrated. The main symptoms were failure offloweringor fertilization, decreased apical growth, small crisped leaves in a terminal rosette and a gradual yellowing of the lower leaves. In combination with low nitrogen, the boron-deficient plants had yellow, succulent leaves at a very early stage. High calcium and high nitrogen increased the demand for boron.

Inoculation with Rhizobium meliloti of plants with a low nitrogen supply was performed with success. The bacteria formed healthy, pink nodules on the roots inside the rockwool cubes.

The lowest content of boron in whole plants showing boron deficiency symptoms (no pods formed) was 13 μg/g and in this respect fenugreek is very similar to lucerne (Medicago sativa), a plant known to have a high boron requirement. Fenugreek has a high tolerance of excess boron.

In a field trial performed within a winter-bean crop (cv. Throws MS) during 1975, Benlate, Bavistin, Cercobin and BAS352F were shown to effect some control over a mild, non-aggressive chocolate spot attack after one foliar application. Following a second foliar application, disease incidence on the leaves was significantly reduced by all except the Cercobin treatment, and reductions in the incidence of aggressive lesions on the leaves and the degree of infection on the pods were effected by all except the BAS352F treatment, indicating this chemical to be non-systemic. A reduced rate of leaf loss was observed for plants treated with Benlate, Bavistin or Cercobin, suggesting that part of the disease control effected by these chemicals might indirectly result from a delay of leaf senescence.

Three experiments were carried out over a 2-year period to study the effect of plant density and spatial arrangement and the time of lifting on yield and root size of carrots. Plant density treatments ranged from 108 to 1553 plants/m2 and plant arrangement was varied by growing the plants in 1-, 2-, 3-, 4-, 5-, 10-, 18- and 36-row systems within a 152 cm bed; there were either two or three harvests in each experiment.

Total plant fresh weight, total root yield and mean root weight were not significantly affected by plant arrangement over the range studied, but they all progressively increased with later harvests. The asymptotic relationships between these yield variables and plant density were adequately described by the equation of Shinozaki & Kira (1956), the relationships being significantly different for each harvest.

Yields of canning-size roots (20–30 mm diameter) were influenced by time of harvest, plant density and the interactions between these two variables. The yield of canning-size roots increased with plant density to a maximum and then declined, the maximum yield being achieved at a higher density with later harvests. In two out of the three experiments there was no effect of spatial arrangement on canning root yields but in the third experiment there was a significant row system × density × harvest interaction.

The numbers of roots harvested per metre of row did not differ significantly between the ‘outer’ and ‘other’ rows for any row system treatment. The mean root weight, however, was consistently greater from the outer rows of systems with three or more rows and this ‘edge’ effect became larger with later harvests.

The results are discussed in relation to other published data and to carrot production. It is concluded that any of the tested row systems are equally satisfactory for carrot production and the choice can be based on such considerations as the availability of suitable harvesting equipment.

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.

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.

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).