Growth and yield of cotton as affected by different straw returning modes with an equivalent carbon input

Abstract

Crop production is greatly affected by the applications of straw and straw-biochar. However, the responses of cotton (Gossypium hirsutum L.) growth and yield to different straw returning modes with an equivalent carbon (C) input are still unclear. A four-year field experiment was conducted to investigate the effects of different straw returning modes on the soil temperature, soil water content, soil nutrient availability, cotton root growth, cotton nutrient status, cotton canopy photosynthetic properties and seedcotton yield in a barley-cotton rotation system in Yancheng, China. Based on an equivalent C input, five treatments were set: straw-biochar incorporation (SB), straw incorporation with microbial inoculant (SI), straw incorporation (S), straw mulching (SM), and the control without straw or straw-biochar (CK). Treatments with straw and straw-biochar significantly enhanced most cotton growth parameters, and consequently increased the seedcotton yield from the second year to the fourth year. Such beneficial effects induced by the applications of straw and straw-biochar tended to progressively increase annually. In the fourth year, seedcotton yields in SB, SI, S and SM were significantly increased by 24.2%, 16.1%, 14.3% and 8.2%, respectively, compared with that of the control. The highest increase in seedcotton yield in SB was due to the greatest improvements in the contents of soil available nitrogen (N), phosphorus (P) and potassium (K); root biomass; NPK uptake by cotton; partitioning percentage of NPK to bolls; and canopy apparent photosynthesis rate. The lowest increase in seedcotton yield in SM was mainly ascribed to a reduction of 2.4–3.2 ℃ in the daily maximum temperature of topsoil at the early growth stage of cotton. Overall, compared with other crop straw returning modes, converting straw into biochar and incorporating it into fields could be an appropriate practice for sustaining high seedcotton yield in the barley-cotton rotation system.