Effect of straw mulching on soil respiration, crop yield, economy-environment benefit in rainfed winter wheat fields

As a common cultivation pattern in the Loess Plateau, straw mulching has played a significant role in increasing grain yield, improving water use efficiency and regulating soil CO₂ emission. A field experiment was conducted to measure the response of soil respiration and crop yield to different straw mulching treatments under winter wheat monoculture system in 2009-2011. Economy-environment benefit, calculated by soil CO₂ emission per unit wheat yield, was also evaluated for each mulching treatment. The four treatments included the control (CK) without mulching, 9 000 kg·hm^-2 (M₉₀₀₀) and 4 500 kg·hm^-2 (M₄₅₀₀) of straw mulching year-round, and 9 000 kg·hm^-2 (SF) straw mulching during summer fallow. The results showed similar variations in soil respiration rates among treatments during crop growth period. No significant differences were noted among mulching treatments in both years in terms of cumulative soil CO₂ emissions during growing season. However, average range of soil CO₂ emission for treatments in the first year 14.92~17.43 t(CO₂)·hm² was significantly higher than that in the second year 12.95~13.69 t(CO₂)·hm². In terms of emitted soil CO₂, the interactions among treatments and year were insignificant. Compared with CK, straw mulching decreased crop yield remarkably. The difference between M₉₀₀₀ and CK was significant at P < 0.05. Economy-environment benefit index suggested that for 1 kg grain produced, the soil released 2.96~3.16 kg CO₂. Straw mulching did not influence average economy-environment benefit. Gran yield and economy-environment benefit varied for the two years. Grain yield in the first year, during which rainfall was less than average, was significantly lower than that in the rainy second year. On the contrary, economy-environment benefit index of the first year (3.03~3.69 kg·kg^-1) was markedly higher than that of the second year (2.45~2.88 kg·kg^-1). Treatments and years had significant interaction effects on grain yield and economy-environment benefit. While straw mulching had the potential to increase grain yield in dry year, M₉₀₀₀ treatment had the best economy-environment benefit value. For rainy years, straw mulching treatments decreased crop yield, while the economy-environment benefit index under CK was fairly good.