Optimum NPK management over extended cropping periods in south-west Cote d'Ivoire

Authors

  • H. Van Reuler
  • B.H. Janssen

DOI:

https://doi.org/10.18174/njas.v44i4.537

Abstract

In the Tai region of south-west Cote d'Ivoire P is the yield-limiting nutrient on (moderately) well drained soils. In order to find the optimum P application rate, a factorial experiment (2N x 4P x 2K) in three replicates was conducted at two sites during six seasons. The factors investigated were N (0 or 50 kg/ha), P (0, 12.5, 25 or 50 kg P) and K (0 or 50 kg K). N (urea) and K (muriate of potash) applications were split into two equal parts and broadcast. From the third season onwards the N application was raised to 100 kg N. P (triple superphosphate) was placed near the young plants. Upland rice and maize were used as test crops. The experimental sites were located at the crest (Site VII) and lower slope (Site VIII) of a catena. In the first season after clearing at Site VII highest yields were obtained with 12.5 kg P and at Site VIII with an application of 25 kg P. At the latter site also N application increased yields. In an extended cropping period the rice yield level could not be maintained. The efficiency of utilization of absorbed P (EUP) of rice was high in the first season after clearing but decreased in subsequent seasons. This is in contrast to EUP for maize which remained constant with time. Hence, it is concluded that the rice yield decline is caused by other factors than nutrient deficiencies. In all seasons yields were higher at Site VII than at Site VIII. The residual effect of fertilizer-P could reasonably well be described by a simple formula: RFP1 = (0.9 - RFP1)t-1 x RFP1, where RFP and RFP1 are the apparent recovery fractions of fertilizer P in year t and year 1, respectively. In all seasons, except in the first season after clearing, the potential P supply was higher at the crest (Site VII) than at the lower slope (Site VIII). Extending the cropping period proved possible when fertilizers were applied and maize was grown. For both sites fertilizer guidelines could be formulated. Comparison of soil chemical data (pH, organic C, total N and total P) before the start of the experiment and after six seasons did not show changes.

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Published

1996-12-01

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Section

Papers