No abstract

teriorate the soil physico-chemical conditions of the often physically and chemically fragile moist savanna soils Nutrient depletion is a major constraint to crop production for in the long term, especially in the case of ammonium moist savanna soils, and inputs of nutrients are required to overcome sulfate [(NH 4 ) 2 SO 4 ] (Pieri, 1992). This observation, tothis constraint. The impact of sole and combined applications of organic inputs (OIs) [fresh tree prunings, Pueraria phaseoloides (Roxb.) Recherche Agronomique, B.P. 1026, Lomé , Togo; J. Diels, N. Sanginga, and O. Lyasse, RCMD, IITA, Ibadan, Nigeria, c/o L.W. Lam-al., 1997), most trials in the West African moist savanna bourn and Co., 26 Dingwall Rd., Croydon CR9 3EE, UK; R. Merckx, deal with manure or crop residues as a source

This paper focuses on testing the Direct Hypothesis using 15N-labelled fertilizers. This hypothesis formulated by Vanlauwe et al. (2001a) originates from data obtained under controlled laboratory conditions showing interactions between organic matter-C and mineral-N. A series of experiments (lysimeter, nanoplots and microplots) with 15N-labelled fertilizer (urea or ammonium sulfate) and organic matter was carried out to test the Direct Hypothesis at different scales. Details of the trials testing the Direct Hypothesis through the use of 15N-labelled fertilizers and organic matter carried on an Arenosol in Ibadan, southwestern Nigeria are discussed.

No abstract

No abstract