Growth and nutrient uptake of Natal Common groundnuts in Tanganyika

Abstract

A study, using the methods of growth analysis, is reported of the accumulation of dry matter in two Natal Common groundnut crops grown at Kongwa, Tanganyika under conditions of relatively low population (26,000 plants/acre) with phosphate fertilizer (F series), and at a higher population (56,000 plants/acre) without fertilizer (O series). The uptake and distribution of N, P, K, Mg and Ca was followed in the F series.In the F series, the dry weight per plant at maturity was 32·7 g., of which 14·9 g. (45%) was kernels, while in the O series the corresponding figures were 20·6 and 10·4 g. The relative growth rates, net assimilation rates and leaf-area ratios were similar in the two crops, with small but consistent advantages to the F series. Nevertheless, the yields per acre were markedly higher in the O series, where total dry-matter and kernel yield were 2540 and 1290 lb./acre, respectively, against 1910 and 870 lb. in the F series. It is shown that this was the result of consistently higher leaf weights per acre and a higher total leaf-weight duration (4180 lb. weeks/acre) in the O series than in the F series, where total leaf weight duration was 2810 lb. weeks/acre.The formation of the kernels continued to maturity in each case, largely at the expense of current assimilation rather than by net translocation from the vegetative parts.The uptake of N, in the F series, reached a total of 63 lb./acre, of which 45 lb. was in the mature kernels. It went largely into the vegetative parts during the first two-thirds of the crop's life, but in the final stages most of the uptake went into the kernels and there was some evidence of translocation of N from the vegetative parts and the shells. N accumulation did not seem to be affected by rainfall fluctuations within the season. The net assimilation rate did not appear to be directly associated with the activity of the plant in accumulating N, but the leaf-area ratio, and the relative growth rate, were associated with the rate of N uptake per unit of plant dry weight.The total P taken up was no more than 4 lb. (of the element) per acre of which nearly 80% was found in the kernels at maturity. There was considerable evidence of translocation of P into the kernels from the vegetative parts of the plant. P uptake (unlike that of N) was heavily reduced in a mid-season dry period, suggesting that P was largely derived from the upper layers of the soil.The total amount of K found in the crop at maturity was about 26 lb./acre, mostly in the vegetative parts. Rather under a fifth was in the kernels, although they constituted 45% of the total dry weight. The data for Ca and Mg are incomplete, but it may be suggested that the maximum accumulation of Ca was around 10 lb./acre, almost all in the vegetative parts, and that of Mg about 5 lb./acre, of which 2 were in the kernels.The grateful thanks of the authors are due to Dr M. T. Friend, of the East African Agriculture and Forestry Research Organisation, Muguga, Kenya, who determined N and P in the samples of the F series, and to Mr G. T. Chamberlain, of the same Organisation, who carried out the estimations of K, Ca and Mg. They would also wish to express their indebtedness to the members of the former Scientific Department of the Overseas Food Corporation who assisted with the work in laboratory and field, and in particular to Mr B. W. Culy, Manager of the Kongwa Experimental Station, who was responsible for the production of the crops.