Positive effect of sorghum grown as a soil-improving crop on the CO2 environment in greenhouses and apparent photosynthesis of strawberry.

摘要

The contribution of freshly applied sorghum grown as a green manure crop, to the CO2 environment of greenhouses was determined for soils containing different amounts of organic carbon. Two growers using different soil management practices for more than 10 years were selected for study. Grower A applied 20 t ha-1 year-1 of commercial farmyard manure, while grower B had grown sorghum in the summer and also applied the same amount of manure as grower A. Soil carbon content was significantly higher in greenhouses of B (2.3%) than those of A (1.5%). In June 1993, sorghum was sown in one greenhouse of each grower and grown for 2 months, while adjacent greenhouses were left without sorghum. The rate of CO2 evolution from the soil was higher in greenhouses of B than those of A. Use of sorghum as green manure in the current season resulted in an increased CO2 evolution rate by ca. 100 ml CO2 m-2 hr-1 in A throughout the measurement period, and consequently an increase in the pre-dawn CO2 concentration of 300 ppm. Although the effect of freshly applied sorghum was smaller in B compared to A, the pre-dawn CO2 concentration in greenhouses of B was 500-1000 ppm higher than that of A. Consequently, net CO2 assimilation and light conversion efficiency of strawberry plants were highest in the greenhouse of B with sorghum, and lowest in that of A without sorghum..