Straw Management Effects on Organic Matter Mineralization and Salinity in Semiarid Agricultural Soils

Abstract

The impact of straw incorporation (6 Mg ha -1 year -1 ) into agricultural soils compared with straw removal on organic matter mineralization and salinity was studied. The mineralization coefficient (CO 2 -C evolved/organic C ratio) was obtained to evaluate organic matter mineralization. Soil salinity was measured as means of electrolytic conductivity of saturation paste extract. Both parameters were measured seasonally during two years in two salt-affected soils of the semiarid Central Ebro Valley (northeast Spain), a saline soil and a saline-sodic soil. The electrolytic conductivity (ranging from 2.5 dS m -1 to 24.3 dS m -1 ) and the mineralization coefficient (ranging from 5.9 10 -4 day -1 to 37.9 10 -4 day -1 ) varied widely during seasonal samplings of both soils. The lowest electrolytic conductivity values, coincided with the highest mineralization coefficient values. Straw mulching and burying decreased significantly the average seasonal electrolytic conductivity of both soils: 2.5 times in the saline soil, and 1.9 times in the saline-sodic soil. The EC reduction only increased significantly (P < 0.05) the mineralization coefficient on saline soil (1.6 times). Straw amendment, followed by rainy periods, allowed the soluble salts leaching but did not modify significantly sodium content. A logarithmic regression was found between mineralization coefficient and electrolytic conductivity (r 2 = 0.41), considering both soils. Infiltration, water aggregate stability, and qCO 2 were improved with the straw amendment, but only in saline soil. Soil differences showed the existence of a double effect: an osmotic and a specific ion effect.