Intercrop mulch affects soil biology and microbial diversity in rainfed transgenic Bt cotton hybrids

Abstract

Growing live mulch between the wide-row spaced transgenic Bt cotton hybrids is a low-cost option to control weeds compared to the use of plastic mulch. However, nothing is known about their effects on soil biology. Therefore, soil samples were collected from a long-term field study (2014–15 to 2018–19) to investigate the soil biological activities as well as the microbial diversity (soil metagenomic analysis). In general, mulching enhanced soil biological activity and influenced the microbial diversity in Bt-cotton. Mulch of sunnhemp (Crotalaria juncea L.), desmodium (Desmodium triflorum L.), sorghum (Sorghum bicolor L.) and plastic sheet recorded significantly higher soil biological activities such as, basal respiration, microbial biomass carbon, and soil enzymes than the other mulch treatments. Aromatic crops (bitter cumin (Centratherum anthelminticum (L.) Kuntze), carom (Trachyspermum ammi (L.) Sprague ex Turrill), coriander (Coriandrum sativum L.), fennel (Foeniculum vulgare Mill.), and fenugreek (Trigonella foenum-graecum L.) had a significant adverse effect on soil biological activity compared to the farmers' practice (no mulch or intercrop). The rarefaction curves as a measure of alpha diversity indicated higher species richness in plastic and newspaper sheet mulch treatments compared to the intercrop mulch. The soil metagenome data indicated Proteobacteria (28%–36%), Actinobacteria (10%–35%), and Acidobacteria (10%–26%) were highly abundant phyla in the mulch treatments. The phyla, Chloroflexi (4%–5%), Gemmatimonadetes (2%–6%), Planctomycetes (2%–4%), and Bacteroidetes (2%–3%) were recorded at lower frequencies in all mulch treatments. The sunnhemp and newspaper mulch treatments recorded low frequency (0.06%–0.07%) of the fungal phyla, Ascomycota. Compared to the bare soil, mulching positively improves soil biological activity. Furthermore, our study identifies some crops that could be grown as an intercrop with a viewpoint to improve soil biology and provide an alternative to the expensive plastic mulch.