THE EFFECT OF STAGE OF GROWTH AT DEFOLIATION ON WHITE CLOVER IN MIXED SWARDS

Four experiments are described in which various defoliation methods and frequencies were imposed on grass/white-clover swards. Clover was not reduced in any of these hy increasing the length of growth period or hy cutting at a late stage of growth, but intensive sheep grazing reduced clover compared nitb cutting and taking a silage cut in a grazing sequence improved clover yield. These results do not support the contention that cutting a mixed sward for hay or silage suppresses clover because of competition for light: with a ‘big white’ type of clover infrequent defoliation may cause no more shading than frequent. Alternatively, any additional shading may be compensated for by an increase in clover growth, stimulated hy the longer growth period. It is suggested that, in practice, competition for nutrients and moisture also contrihute towards clover suppression when swards are cut for hay or silage.     

Effects of substituted p-benzoquinones on urease activity in soils

The effectiveness of substituted p-benzoquinones as inhibitors of urease activity in soils depends largely upon their substituent groups. Methyl, chloro-, bromo- and fluoro-substituted p-benzoquinones have a marked inhibitory effect on soil urease activity, whereas phenyl-, r-butyl-and hydroxy-substituted p-benzoquinones have little, if any, effect. Methyl-substituted p-benzoquinones differ from other substituted p-benzoquinones in that their effects on soil urease activity usually increase markedly with increase in their time of contact with soil.A study of the effects of selected substituted p-benzoquinones on urea hydrolysis and volatilization of urea N as ammonia in a sandy soil treated with urea showed that methyl- and chloro-substituted p-benzoquinones had very marked effects, whereas hydroxy- and phenyl-substituted p-benzoquinones had little or no effect. Gaseous loss of urea N as ammonia when this soil was incubated at 20°C for 14 days was reduced from 62.8 to 0.1 per cent by addition of 2,3-dimethyl-, 2,5-dimethyl-, or 2,6-dimethyl-p-benzoquinone (2.3 parts/100 parts of urea).The work reported indicates that, of the 34 substituted p-benzoquinones studied, 2,3-dimethyl-, 2, 5-dimethyl- and 2,6-dimethyl-p-benzoquinone are likely to prove the most effective for retardation of urea decomposition in soils and reduction of the problems caused by the normally rapid hydrolysis of fertilizer urea by soil urease.     

THE ELECTRONIC MEASUREMENT OF SMALL HERBAGE YIELDS USING A HIGH SENSITIVITY CAPACITANCE METER

The capacitance meters available in the past for estimating herbage yields have lacked sensitivity at the extremes of their range of measurement. The preliminary evaluation of a highly sensitive capacitance meter described here indicates that accurate measurement is possible in the range 0.1100 kg DM/ha. The implications of this development for the measurement of herbage of low availability are discussed.