Lime and phosphorus effects on the dry matter production of eragrostis curvula on dystrophic clay soils

Abstract

The dry matter yield responses of Eragrostis curvula to P and lime over two seasons on Balmoral and Balgowan soil series in the Natal Mistbelt are discussed. With this work forming part of a study aimed at characterizing P fixation in these soils, P (0, 100, 300 and 600 kg P/ha) and lime (0, 2 000 and 6 000 kg/ha as calcium hydroxide), were applied three years prior to establishment of E. curvula. Highly significant yield responses to P were noted, P effects being particularly dramatic at establishment, when response continued to the highest P level. Yields over the two seasons were closely related to soil test (AMBIC) values, with a threshold P test of 7mg/L being indicated. E. curvula displayed a remarkable ability to tolerate soil acidity, and yield responses to lime, although significant, were not nearly as marked as responses to P. In the absence of lime, where acidity was severe (pH[KCl] = 3,8 to 3,9; soil acid saturation = 60 to 80 %) yields were 87 to 97 % of those attained with the highest lime level.

Uittreksel

Die reaksie van droëmateriaal‐opbrengs van Eragrostis curvula op P en kalk in Balmoral‐ en Balgowangrondserie oor twee seisoene in die Natalse Misbelt word bespreek. Hierdie werk vorm deel van ‘n studie wat gemik is op die karakterisering van P‐binding in genoemde grondsoorte. Fosfor (0, 100, 300 en 600 kg/ P/ha) en kalk (0, 2 000 en 6 000 kg/ha as kalsiumhidroksied) is drie jaar voordat E. curvula gevestig is toegedien. Hoogs betekenisvolle opbrengsreaksies op P‐toediening is gevind. Die reaksie was veral opsigtelik gedurende die eerste snysel na vestiging, waartydens opbrengs bykans reglynig toegeneem het soos die P‐peil verhoog het. Opbrengste oor die twee seisoene het ‘n noue verwantskap met grondontledings (AMBIC) getoon en ontledings het ‘n minimum drempelwaarde vir P van 7mg/L aangedui. E. curvula vertoon ‘n merkwaardige verdraagsaamheid teenoor grond‐suurheid. Die opbrengsreaksie op kalk, alhoewel betekenisvol, was nie naastenby so duidelik soos die reaksie op P nie. In die afwesigheid van kalk, waar die suurheidsgraad baie hoog was (pH[KCl] = 3,8 tot 3,9; grondsuurversadiging = 60 tot 80 %) is opbrengste van 87 tot 97% die met die hoogste kalk vlak verkry.

Additional index words:

• Exchangeable acidity
• P fixation
• P soil tests

Notes

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