Remote Sensing-Assisted Physical Modelling of Complex Spatio Temporal Nitrate Leaching Patterns from Silvopastoral Systems

Summary

Affordable optical data obtained from Unmanned Aerial Vehicle (UAV) coupled with process-based model could constitute an integrative platform to map complex spatio-temporal patterns of nitrate leaching and reduce uncertainties in tightening the nitrogen (N) cycle of silvopastoral systems. This study uses field data from commercial farm in Denmark with lactating sows housed in paddocks with pasture flanking a central poplar tree zone either pruned (P) or unpruned (tall, T), each with resources (feed and hut) on same (S) or opposite side (O) of the tree zone. Poplar leaf area index derived from true-colour UAV imagery was fed to the Daisy process-based model alongside soil data and geostatistical analyses to derive the soil water balance across the paddocks and explicitly map the spatio-temporal variation of soil nitrate leaching at 1 m. Nitrate leaching varied seasonally and spatially from 7 to 860 kg N ha−1 year−1, a wide range otherwise difficult to capture by employing only process-based model using mean effective parameters. Nitrate leaching was in the order PO > PS > TO > TS. The N cycle was tightened with T regardless of S/O. The approach could operationally monitor complex silvopastoral systems where trees and resource position play the role to alleviate nitrate leaching in outdoor pig systems.