Carbon and nitrogen mineralization at different salinity levels in Omani low organic matter soils

Abstract

A 56-d incubation experiment at 30 °C was carried out to study how salinity affects C and N mineralization of composted dairy manure and date palm straw. A low- and a high-saline soil were amended with (1) manure, (2) manure + low straw, (3) manure + straw, and (4) sole straw. The microbial and fungal biomass contents are very low in Omani soil abandoned for at least 6 years. Straw application revealed a highly significant increase in microbial biomass C, but especially in ergosterol in the low-saline soil. In contrast, straw led only to an increase in ergosterol in the high-saline soil, where only the combined application of manure with straw had significant positive effects on microbial biomass C. In the high-saline soil, the sum of C mineralized reached only 55% of SOC-derived CO2–C, 65% of manure-derived CO2–C, and 75% of straw-derived CO2–C in comparison with the respective treatments of the low-saline soil. The application of straw led always to a net N immobilization, which was markedly stronger in the high- than in the low-saline soil. The increase in salinity by composted cattle manure should be considered if this fertilizer is applied to soils sensitive to changes in salinity.