Effect of plant biomass and their incorporation depth on organic wheat produc-tion in Kenya

Summary

Intensive agricultural technologies introduced in Africa some six decades ago paved the way for extensive land clearing and destruction of organic materials, development of high yielding crop varieties under monoculture and replacement of landraces. Si-multaneously, pesticides and antibiotics for use in agricultural pest and disease control were being developed and soon the face of agriculture was transformed by what was termed the Green Revolution. However, the apparent success accruing from such heavy investment was short-lived since the system would easily succumb to soil erosion, reduced soil organic matter, environmental pollution and pest and disease outbreaks. The inevitable result is the inability of land to sustain food productivity and worsening poverty. In response to these dangers, organic agriculture is considered a viable approach which meets the critical need for food security, food safety, as well as human and environmental health. The use of naturally occurring and locally available farm inputs such are plant materials, animal manures and mineral nutrient rich rock ores such as rock phosphates as plant nutrient sources are instrumental in refurbish-ing soil fertility in a sustainable and economical way. In this experiment, green ma-nures derived from Tithonia diversifolia, Dolichos lablab and Tephrosia vogelli were evaluated for their effect on the performance of organically grown wheat. These mate-rials were incorporated at different soil depths namely; 0 cm (mulch), 15 cm and 30 cm deep. Rock phosphate was used as a source of phosphorus and wheat was planted 2 weeks after incorporation. Significant yield increase (15% higher than the untreated control) was observed in the Tithonia treatment. This was attributed to the high nutri-ent concentrations and the quick release of these nutrients in the tissues of Tithonia. Shallow applications of the plant materials also gave better responses than deep application. Apparently, shallow applications are appropriate for shallow rotted crops like wheat. It was concluded that locally available plant material of high nutrient con-centrations which decompose easily to release its nutrients can complement other soil management packages for organic crops in Kenya.