The influence of soil phosphorus, pH and texture on the uptake of phosphorus from soil and fertilizer by upland rice

  • H. Van Reuler
  • B.H. Janssen


At six sites in 1987, and two sites in 1988 in the Tai region of south-west Cote d'Ivoire, long-term field trials were started to study the supply of nutrients from the soil and the response of food crops to fertilizers. The results for P during the first season after removal of the primary or secondary forest vegetation in experiments with rice are described. P rates were 0 or 50 kg/ha in 1987, and 0, 12.5, 25 or 50 kg in 1988. The application of 50 kg P increased grain yield by 0.5-1.0 t/ha at five of the six sites in 1987. In 1988, a similar response could be obtained with lower rates of 12.5 or 25 kg P ha. At all sites, P application increased P uptake significantly, but the recovery of fertilizer P decreased with increasing P application rates. The soil P supply was best described by an equation including P-Dabin (a modified P-Olsen method), total P and pH. The recovery of fertilizer P could best be described by equations including silt plus clay content, P-Dabin, and/or total P. Since some soils had a high gravel content, soil analytical data, referring to the fine earth (<2 mm) fraction of the soils and expressed on a mass basis, were translated to values expressed on the basis of volume of total soil. This conversion substantially improved the relations between soil properties and P uptake or fertilizer-P recovery.