Meta-analysis reveals that returning crop straw to arable land causes soil acidification at the global scale

Abstract

Returning crop straw to arable lands has been recommended as an appealing practice of climate-smart agriculture. On the other hand, straw return (SR) may also change soil pH that crucially regulates soil productivity and environmental quality. However, the magnitude and controlling factors of this SR-induced soil pH change remain largely uncertain, limiting our ability to fully assess its impacts on soil health and environmental quality. Here, we conducted an integrative synthesis of SR-induced soil pH change using a database comprising 326 treatment-pairs at 175 sites across the globe. Overall, SR caused significant (P < 0.01) decline in soil pH, with an average magnitude of −0.030 ± 0.024 (95 % confidence interval, CI) units and an annual change rate of −0.015 ± 0.006 (95 % CI) units, compared with the non-SR reference. Specifically, SR-induced soil pH change varied substantially with local agricultural managements and environmental conditions, of which initial soil pH and land use type were identified as the two most-important factors. Straw return decreased soil pH in alkaline soils but increased pH in acidic soils, leading to a negative correlation between SR-induced soil pH change and its initial value. Straw return caused soil pH decline both in dry and paddy lands, while the decline magnitude in paddy lands was twice as large as in dry lands. By highlighting the risk of SR-induced soil acidification, our results provide new insights to evaluate the agro-environmental consequences of straw return practice, which will help to develop the region-specific tailored straw utilization policies.