Articles | Volume 6, issue 3
Solid Earth, 6, 1063–1073, 2015
Solid Earth, 6, 1063–1073, 2015

Research article 17 Sep 2015

Research article | 17 Sep 2015

Precision of farmer-based fertility ratings and soil organic carbon for crop production on a Ferralsol

P. Musinguzi1, P. Ebanyat1,2, J. S. Tenywa1, T. A. Basamba1, M. M. Tenywa1, and D. Mubiru3 P. Musinguzi et al.
  • 1Department of Agricultural Production, Makerere University, P.O. Box 7062, Kampala, Uganda
  • 2International Institute of Tropical Agriculture (IITA), Plot 15, Naguru East Road, P.O. Box 7878, Kampala, Uganda
  • 3National Agricultural Research Laboratories, Kawanda, P.O. Box 7064 Kampala, Uganda

Abstract. Simple and affordable soil fertility ratings are essential, particularly for the resource-constrained farmers in sub-Saharan Africa (SSA), in planning and implementing prudent interventions. A study was conducted on Ferralsols in Uganda to evaluate farmer-based soil fertility assessment techniques, hereafter referred to as farmers' field experiences (FFE), for ease of use and precision, against more formal scientific quantitative ratings using soil organic carbon (SQR-SOC). A total of 30 fields were investigated and rated using both techniques, as low, medium and high in terms of soil fertility – with maize as the test crop. Both soil fertility rating techniques were fairly precise in delineating soil fertility classes, though the FFE was inefficient in distinguishing fields > 1.2 % SOC with medium and high fertility. Soil organic carbon, silt and clay were exceptionally influential, accounting for the highest percentage in grain yield of 50 % in the topsoil (0–15 cm) and 67 % for the mean concentrations from 0 to 15 and 15 to 30 cm. Each unit increase in SOC concentration resulted in 966 to 1223 kg ha−1 yield gain. The FFE technique was effective in identifying low-fertility fields, and this was coherent with the fields categorized as low (SOC < 1.2 %). Beyond this level, its precision can be remarkably increased when supplemented with the SQR-SOC technique.

Short summary
This study showed that resource-poor smallholder farmers can ably rate fields for soil fertility as poor or good but had difficulties in identifying medium-fertility fields. Rating with SOC improved precision to rate medium-fertility fields. SOC and clay content explained the highest yield variances in heterogeneous smallholder farms. A combination of SOC and farmers' field experiences can be affordable approaches to guide fertility management and fertilizer application.