Effects of Different Drip Irrigation Belt Layout Modes on Soil Allelochemicals and Microorganisms in Apple - Soybean Intercropping System 

This study aimed to investigate the impact of different layouts of drip irrigation belts on the distribution of soil phenolic acids, enzyme activities, and microorganisms in a fruit-crop intercropping system. Specifically, we focused on the apple-soybean intercropping system in the loess region of western Shanxi. Three types of drip irrigation belt spacing (L1, L2, and L3) were employed in the study: L1 involved the arrangement of a drip irrigation belt for each row of soybean, L2 had a drip irrigation belt at intervals of one row of soybean, and L3 had a drip irrigation belt for the third row of soybean from the fruit tree.We analyzed the spatial distribution changes of soil phenolic substances, enzyme activity, and microbial quantity under different water distributions. Principal component analysis was then applied to establish the relationship between soil factors and drip irrigation treatments.The results indicated that, apart from benzoic acid and phloroglucinol, the spacing of the drip irrigation belt significantly influenced the distribution of phenolic acids in the soil. Likewise, except for catalase, the spacing of the drip irrigation belt had a significant impact on the distribution of enzyme activity and microbial quantity. The effects of different drip irrigation belt layout modes on the distribution of soil phenolic acids, bacteria, and fungi were consistent with those observed in the intercropping control treatment, where the distribution increased as the distance from the tree increased. Enzymatic activity decreased initially and then increased with increasing distance from the tree under drip irrigation.Principal component analysis revealed that different drip irrigation belt spacings altered the content of soil allelochemicals, microbial quantity, and enzymatic activity. Additionally, the total amount of phenolic acids in intercropping soil was found to be lower than that in monocropping. Treatment L1 exhibited the highest soil enzyme activity and total microbial biomass, while treatment L2 had the lowest accumulation of phenolic acids in the soil. Notably, treatment L2 demonstrated relatively high soil enzyme activity, despite the lowest accumulation of phenolic acids. Based on our findings, we recommend adopting the arrangement of a drip irrigation belt at intervals of one row of soybean in fruit-crop intercropping systems. This layout not only improves the soil micro-ecological environment but also alleviates the inhibition of allelochemicals.