Abstract: This study aimed to understand the effects of cover cropping and organic fertilization on soil labile organic carbon pool in Goji (Lycium barbarum L.) fields in an arid region of Ningxia. There were six treatments, including L. barbarum monocropping + no fertilization (S₀), L. barbarum monocropping + medium-level organic fertilization (2 kg·plant^-1, S₁), L. barbarum monocropping + high-level organic fertilization (4 kg·plant^-1, S₂), L. barbarum/radish (Raphanus sativus L.) intercropping + no fertilization (M₀), L. barbarum/R. sativus intercropping + medium-level organic fertilization (2 kg·plant^-1, M₁), and L. barbarum/R. sativus intercropping + high-level organic fertilization (4 kg·plant^-1, M₂). We measured the contents of soil labile organic carbon fractions, carbon pool management index, and analyzed the relationships between carbon pool management index and other physicochemical factors. The main factors driving variation in carbon pool management index were identified by structural equation model. The results showed that compared with the traditional L. barbarum monocropping, L. barbarum/R. sativus intercropping increased readily oxidizable organic carbon content, dissolved organic carbon content, and microbial biomass carbon (by 55.3%, 25.2%, and 79.0%, respectively), as well as in carbon lability, carbon lability index, and carbon pool management index (by 18.4%, 26.8%, and 18.4%, respectively) in the 0-20 cm soil layer (P<0.05). There were no significant changes in the contents of organic carbon fractions and carbon pool management index in the 20-40 cm soil layer. Compared with no organic fertilization, carbon lability and carbon lability index of 0-20 cm soil layer significantly increased in the S₁ and M₁ treatments with medium-level organic fertilization. Under high-level organic fertilization, the carbon lability, carbon lability index, and carbon pool management index of 0-20 cm soil layer significantly increased in the M₂ treatment only, by 61.9%, 59.4%, and 64.9%, respectively (P<0.05). In the 20-40 cm soil layer, the carbon pool index of S₁ and S₂ treatments significantly decreased, with minimal changes in the contents of organic carbon fractions and carbon pool management index of M1 and M₂ treatments. Results of the structural equation model showed that organic carbon content, readily oxidizable organic carbon content, dissolved organic carbon content, microbial biomass carbon, and total nitrogen content together explained 98% of the variation in carbon pool management index. Our results indicated that the intercropping pattern of L. barbarum and R. sativus could effectively increase soil labile organic carbon content and achieve the purpose of improving soil fertility with reduced application of organic fertilizer in the arid region of Ningxia.

Key words: cover crop, organic carbon fraction, labile carbon pool, carbon pool management index, structural equation model