Original Articles

Relationship between inorganic soil nitrogen and maize grain yield with controlled traffic practices

Published in: South African Journal of Plant and Soil
Volume 23, issue 3, 2006 , pages: 190–196
DOI: 10.1080/02571862.2006.10634753
Author(s): C., J.J. Schmidt, South Africa, S.A. Smalberger, South Africa, S.A. Smalberger, South Africa, F.G. Adriaanse, South Africa, C.C. du Preez, South Africa


Traditional N fertilizer guidelines were based on relationships between N application rates and yield response. These relationships varied greatly according to residual inorganic N content in the soil. The objective of this study was to establish inorganic N threshold values for maize production on a specific soil that could also be extrapolated to similar conditions. During the 1993/94 season a site situated near Viljoenskroon (27°10'S, 26°55'E) on a sandy Clovelly soil form was selected for a N×P fertilizer trial. Five N application rates (0, 40, 80, 120 and 180 kg N ha−1) and five P application rates (0, 10, 20, 40 and 60 kg P ha−1) were factorially combined and replicated thrice according to a randomised block design. Treatments were repeated for five consecutive seasons on the same plots. Over seasons 100% relative yield was obtained at an inorganic N threshold value of 74 kg N ha−1, 90% at 56 kg N ha−1, 80% at 45 kg N ha−1, 70% at 35 kg N ha−1, 60% at 27 kg N ha-1 and 50% at 20 kg N ha−1, measured approximately six weeks after planting in the 0–600 mm soil layer for the total soil volume. Values for soil volumes over rows were very similar. An average N requirement factor of 2.3 kg N applied per kg N measured was calculated for soil volumes over rows, as well as for total soil volumes, in the top 600 mm soil according to linear models. Thus by taking the inorganic N threshold values, the N requirement factor and the measured inorganic N level in the soil into account, an actual N recommendation can be calculated in order to obtain a specific relative yield between 50 and 100%. Farmers should for economic reasons be encouraged to manage inorganic N levels in the soil to obtain a certain percentage of the expected yield. Inorganic N threshold values can be extrapolated to similar soils varying in inorganic N content.

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