Can silvopasture with arboreal legumes increase root mass at deeper soil layers and improve soil aggregation?

Silvopastoral system (SPS) is a multifunctional agroforestry practice. This study evaluate soil properties and root biomass under SPS in Pernambuco, Brazil. The experiment was established in 2011. The treatments were (1) monoculture signalgrass (MS) [Urochloa decumbens (Stapf.) R. D. Webster], (2) intercropped pasture of signalgrass with legume Gliricidia (SG) [Gliricidia sepium (Jacq.) Steud.], and (3) intercropped pasture of signalgrass with legume sabiá (SS) (Mimosa caesalpiniifolia Benth). Treatments were allocated in randomized complete block design with three replications. Samples were collected at 0- to 10-, 10- to 20-, 20- to 40-, 40- to 60-, 60- to 80-, 80- to 100-, and 100- to 120-cm soil depths. Soil samples were also taken from the native forest (NF) considered as a reference at the same Experimental Station. Legume SPS (SG and SS) presented greater root biomass per unit area compared to MS at 60- to 80-cm depth (p < 0.05); however, MS had greater root biomass per hectare at the top layers. The average values of the weighted mean diameter of soil aggregates were 3.20, 3.19, 3.07, and 3.27 mm in MS, SG, SS, and NF, respectively, at 0- to 120-cm depths. The SPS increased soil cation exchange capacity in deeper layers, indicating greater biological activity at greater depth. Grasslands and SPS store 235 Mg C ha−1 with 71% of that found in deeper layers (20–120 cm). SPS with signalgrass intercropped with arboreal legumes has potential to improve deep soil C storage and resilience of livestock systems in tropical regions.