THE USE OF FERTILISER IN WATTLE CULTURE

Abstract

Summary A COMPREHENSIVE series of replicated and other experiments laid out between 1927 and 1938 on the estates of the Natal Tanning Extract Company to test the efficacy of artificial fertilisers in wattle culture are described and the results thereof are analysed. It is concluded that it is possible to increase the yields of wattle plantations materially and profitably by the use of artificial fertilisers, provided that optimum sylvicultural practices are adopted and overcrowding and suppression during youth are avoided. The response to fertiliser varies with soil depth, rainfall and humidity, and soil constitution. On shallow soils response is negligible, but on soils of moderate to good depth it is satisfactory and in such cases is much greater in dry areas than in moist. On sandstone soils between 100 and 200 lb. of superphosphate per acre at the start of each rotation may be expected to increase yields by about 10% on the average, gaining say ¾ ton of green bark per acre, but greater applications of fertiliser give no additional response on such soils. On clay soils in Natal and Zululand 400 lb. of superphosphate per acre (larger applications have not yet been tried) at the start of each rotation may be expected to increase yields by about 15% or slightly over 1 ton of green bark per acre. In the Eastern Transvaal 400 lb. of superphosphate per acre at the start of each rotation may be expected to increase yields from 20% to 50%, depending on soil depth, or from 1¼ to 3 tons of green bark per acre. Here there is an added advantage in that the fertiliser aids trees to resist frost damage. The best time to apply the fertiliser is within the first six months of the tree's life and fertilisers of rapid action are therefore superior to those of slower action. Superphosphate is the most successful of any of the fertilisers yet tested on wattles. It should not be broadcast but should be dug into the soil close to, though not in contact with, seed or young plants. Raw phosphate, mixtures of super and raw phosphate, basic slag and lime also serve to increase yield but are less efficient. Disease rate and bark quality are not materially affected by fertiliser.