Soil Nitrate Variations Under Grass, Sorghum and Bare Fallow in Semi-Arid Kenya

Abstract

Topsoil nitrate was measured every few days under grass, sorghum and bare fallow at two sites in lower Embu District, Kenya. Concentrations were highest soon after the start of rain and within a week most nitrate had been lost. Under bare fallow and sorghum, nitrate concentration increased during dry weather and losses occurred when soil water content exceeded 10%. Modelling of soil water movement indicated that there was no leaching below the rooting zone, so denitri®cation may be the main route for loss of soil nitrogen. Application of nitrogen fertilizer early in the season is not recommended as it would be lost with the native soil nitrate. The use of phosphorus fertilizer at the phosphorus-de®cient site reduced soil nitrate concentration throughout the season and increased nitrogen uptake by sorghum. At the phosphorus-rich site, vigorous sorghum growth kept the soil nitrate concentration low, even though much nitrate was produced and lost in bare fallow. Adequate soil phosphorus is considered essential if the natural nitrogen resources of the soil are to be managed eciently.

Conservation tillage, local organic resources and nitrogen fertilizer combinations affect maize productivity, soil structure and nutrient balances in semi-arid Kenya

“…The soils, classified as chromic cambisols (Warren et al 1997), had 65% sand, 22% clay and 13% silt. Chemical analysis was done at the main plot level because the field was observed to exhibit some variability.…”

Dynamics of the Nitrogen-Efficient Guild and Its Relationship to Nitrogen and Carbon Patterns in Two Desert Soil Ecosystems

“…However, Herman and others (1993) found no signi® cant increase in the nitrogen ® xer population with nitrogen addition alone. We therefore assume that the signi® cant correlation between NEG and TSN results from a signi® cant correlation between TSN and soil moisture, which mainly governs TSN level (Chiang et al, 1983;Mazzarino et al, 1996;Warren et al, 1997). However, in our results, TOC exhibited a greater effect on the population of nitrogen ® xers than on TSN, since soil moisture had a pronounced effect on TOC.…”

Responses of Inorganic Nitrogen of Forest Soils to Urbanization in Pearl River Delta, South China

“…The conversion of ammonium into nitrate via nitrification also contributed to N leaching [6]. Heavy precipitation [55] and low phosphorus availability [56] could accelerate nitrate leaching in this region. Leached nitrate entering rivers or lakes could contribute to eutrophication [57].…”