MANURES AND WEEDS.

New Zealand Herald, Volume LXVIII, Issue 20761, 2 January 1931, Page 14

MANURES AND WEEDS.

EFFECTS OF LIME. Dr. Winifred E. Brcnchley,. dealing with tho influences of fertilisers on meadow hay, showed that fertilisers exercise an indirect, as well as direct, action on yield on grass and arable land by influencing tho growth of plants other than the desired crop, so varying the degree of' competition to which the clop is subjected. The. composition of weeds or undesirable plants is a much more important factor in determining yield than is generally recognised. On arable land the type of manuring thai is favourable 'to good crop production also favours the growth of weeds. If seasonal conditions encourage the germination and growth of weed seeds before the crop makes headway, tho competition causes serious reduction of crop yield, which is frequently more marked with heavy than with light manuring. The potential weed flora may be very abundant, quantitative experiments at Rothamsted showing that the number of viable weed soeds buried in tho soil may run into hundreds of millions per aero with certain types of fertilisers. On grassland tho effect of ar.iscial fertilisers is variously influenced, by liming On heavy land long-continued treatment with sulphate of ammonia and minerals tends to produce acid soil conditions, and the production of a herbage composed of the less desirable grasses and giving relatively low yiold. Liming under these conditions increases yield greatly, and changes tho balance of composition in favour of more desirable species. On the other hand, on tho samo soil liming has much less or no beneficial effect with onesided manures, such as superphosphate alone, or where the soil is tending toward an alkaline reaction due to the use of nitrate of soda and minerals;