Straw return increases crop production by improving soil organic carbon sequestration and soil aggregation in a long-term wheat-cotton cropping system

Straw return is a promising strategy for managing soil organic carbon(SOC)and improving yield stability.However,the optimal straw return strategy for sustainable crop production in the wheat(Triticum aestivum L.)-cotton(Gossypium hirsutum L.)cropping system remains uncertain.The objective of this study was to quantify the long-term(10 years)impact of carbon(C)input on SOC sequestration,soil aggregation and crop yields in a wheat-cotton cropping system in the Yangtze River Valley,China.Five treatments were arranged with a single-factor randomized design as follows:no straw return(Control),return of wheat straw only(Wt),return of cotton straw only(Ct),return of 50%wheat and 50%cotton straw(Wh-Ch)and return of 100%wheat and 100%cotton straw(Wt-Ct).In comparison to the Control,the SOC content increased by 8.4 to 20.2%under straw return.A significant linear positive correlation between SOC sequestration and C input(1.42-7.19 Mg ha^(−1)yr^(−1))(P<0.05)was detected.The percentages of aggregates of sizes>2 and 1-2 mm at the 0-20 cm soil depth were also significantly elevated under straw return,with the greatest increase of the aggregate stability in the Wt-Ct treatment(28.1%).The average wheat yields increased by 12.4-36.0%and cotton yields increased by 29.4-73.7%,and significantly linear positive correlations were also detected between C input and the yields of wheat and cotton.The average sustainable yield index(SYI)reached a maximum value of 0.69 when the C input was 7.08 Mg ha^(−1)yr^(−1),which was close to the maximum value(SYI of 0.69,C input of 7.19 Mg ha^(−1)yr^(-1))in the Wt-Ct treatment.Overall,the return of both wheat and cotton straw was the best strategy for improving SOC sequestration,soil aggregation,yields and their sustainability in the wheat-cotton rotation system.

Spectral and Photosynthetic Characteristics of Cotton under Chemical-controlled Topping Technology

[Objective] The paper was to study the effect of chemical-controlled topping technology on spectral and photosynthetic characteristics of cotton. [Method] Two row spacing configurations and four topping treatments were set in the experiment field, and the spectral and photosynthetic characteristics of cotton under different configurations and topping treatments were analyzed. [Result] There was no significant difference in spectral reflectance of cotton leaves and canopy among all treatments(T1-T8) before topping. After topping, the spectral reflectance of cotton leaves showed little difference in visible light band, but significant differences in near-infrared light band under two row spacing configurations(T2-T4, T6-T8).And in near-infrared band, compared with CK(T1, T5), the reflectance increased and then decreased under close planting with equal row spacing configurations(T2-T4) and narrow row dense planting configurations(T6-T8). However, the change of cotton canopy reflectance in short infrared bands increased first and then decreased under close planting with equal row spacing configuration, and increased constantly under narrow row dense planting configuration. The photosynthetic capacity of leaves increased, and the net photosynthetic rate(A), stomatal conductance(GH_(2O)),transpirationrate(E) and intercellular CO_(2) concentration(Ci) significantly increased by controlling the top with chemicals, and differences were ob-served between two configurations. After topping treatments, the leaf area of apical leaf increased, and chemical-controlled topping treatments had significant difference with the control. The apical cotton leaves were shrunk internally, and the plant height increased gradually by 7-15 cm;the number of fruit branches increased by 2-4, and the area of apical leaves decreased significantly in chemical-controlled topping treatments.[Conclusion] After topping with chemicals, the spectral characteristics of cotton change, the photosynthetic capacity of leaves is improved, and the growth of apical leaves and apex of cotton is inhibited.