Scientific Paper

Evidence of Induced Nutrient Deficiency in Pine Plantings on Previously Cropped Lands

Published in: South African Forestry Journal
Volume 165, issue 1, 1993 , pages: 1–8
DOI: 10.1080/00382167.1993.9629383
Author(s): A.W. Schumann, South Africa, A.D. Noble, South Africa

Abstract

Widespread establishment failures of Pinus species have recently occurred on agricultural land acquired for commercial forestry in South Africa. These include about 10 000 ha of previously tilled soils in the north-eastern Cape belonging to Mondi Forests. A lettuce (Lactuca sativa L.) bioassay and P. l patula pot trial with five topsoils investigated the role of allelopathy from crop residue degradation in this problem and the response of degraded agricultural soil to amelioration. Cold aqueous extracts of corn crop residue were highly inhibitory to lettuce seedling root growth. Heat sterilisation was able to neutralise the allelopathic effect of corn residue, while activated charcoal was unable to ameliorate the extract solutions. The best amelioration of both grassland and cropped topsoils tested with pine seedlings was fertilisation with Chemicult® and soil sterilisation with methyl bromide or steam. These soil treatments yielded pine seedling growth and foliar nitrogen (N) levels comparable to that achieved with an optimally grown pine bark standard. Fascicle N of pine seedlings grown on unameliorated crop soil was considered severely deficient (1,073%) for growth and produced visible N-deficiency symptoms. Foliar phosphorus (P) was considered sufficient for pine growth. Adequate N nutrition of pines on previously cropped lands was considered to be crucial for their successful establishment. The associated role of allelopathy in the induction of these nutrient deficienciesl and the acceleration of nutrient stressedl seedling mortality through soil pathogens in the field are also recognised.

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