Changes in mineral content and CO2 release from organic greenhouse soils incubated under two different temperatures and moisture conditions

Summary

In organic greenhouse vegetable productions, the turnover rate of organic amendments may be a limiting factor for optimal crop productivity and quality. Hence, we determined the mineralization potential of several organic greenhouse soils maintained at two temperatures (17, 23C) and water potentials (–35, –250 mbars). Replicate cores of structurally intact soils were collected in plastic cylinders, saturated with water and adjusted to the appropriate matric potential. Additional soil samples were sieved, placed in glass jars and incubated under the same treatment conditions. Soil nutrients, gas concentration (O2, CO2, N2O) and microbial activity (CO2 release) were measured over a 25-week period during aerobic incubation. Large variations in nutrient and organic matter content were observed among intact soil samples. CO2 efflux declined exponentially with time, decreases being most apparent in soils having high organic matter content. An increase in temperature lead to enhanced soil respiration rates, mainly during the first weeks of incubation. Overall, mineralization rates were only slightly affected by moisture level or temperature. Gas diffusion, and thus soil biological activity, may be momentarily hindered during frequent irrigations. Yet, our findings indicate that in general matric potentials of –35 and –250 mbars both result in similar mineralization rates in these soils.