Crop–livestock integration enhanced soil aggregate-associated carbon and nitrogen, and phospholipid fatty acid

Integrated crop–livestock (ICL) production enhances diversification and provides ecosystem benefits by improving nutrient cycling and energy efficiency, thus, increasing overall farm productivity. However, a detailed study is needed to understand the influence of crop diversification and grazing animals on soil aggregation and associated carbon (C) and nitrogen (N), and microbial properties, especially compared with a grazed native pasture. We investigated the soil aggregate size distribution and associated C and N fractions, glomalin-related soil protein, and soil phospholipid fatty acid (PLFA) to understand the collective influence of livestock grazing of crop residue and cover crops (CC) and compared it with native pasture and non-grazed traditional production systems. The study was conducted in South Dakota at four different locations consisting of three long-term (> 30 years) on-farm sites: 1 (Salem), 2 (Bristol), 3 (Bristol) with three treatments that included ICL (corn, Zea Mays L.-soybean, Glycine max L.-oats, Avena sativa L.-CC with cattle grazing); natural ecosystem (NE) or native pasture; and control (CNT) (corn–soybean-without grazing or CC). Experimental site 4 (Beresford) with study duration of 3-year consisted of oats, oats with CC, oats with CC + grazing, and grazed pasture mix. Soil samples were collected from 0 to 5 cm depth at all four sites in summer 2019. Data showed that at sites 1 and 2, ICL had significantly (P ≤ 0.5) greater fractionation of 0.053–0.25 mm and > 4 mm aggregates compared with NE and CNT. At site 1, ICL showed significantly higher soil organic carbon (SOC, 36–49%) and higher nitrogen (33–44%) in > 4 mm aggregates than NE and CNT. At site 2, ICL had 32–41% higher SOC than NE and CNT for 0.25–0.5 mm aggregates. At site 1, NE enhanced total phospholipid fatty acid (PLFA), total bacterial biomass, gram (+), gram (−) bacteria than CNT, however, it did not vary significantly than ICL. Grazed pasture mix at site 4 had higher total PLFA (40.81 nmol g(−1) soil) than the other treatments. The principal components 1 and 2 accounted for 33% and 22% of the variation, respectively, where the majority of the microbial compositions and aggregate-associated C and N were influenced by ICL and NE compared with corn–soybean without grazing or short-term oats/CC/grazing treatments. Integrated crop–livestock system and NE enhanced C and N concentrations in macroaggregates as well as in microaggregates. It is concluded that ICL and NE systems are sustainable prospects in enhancing overall soil health. Integrating crop and livestock improved physicochemical and microbial properties compared to the traditional corn–soybean system.