Zonejection: Conservation tillage manure nutrient delivery system
Manure application in minimum till (MT) systems is a challenge worthy of attention because residue cover is a keystone for environmental protection. To develop a system combining zone tillage and manure application into one operation (zonejection), two experiments were conducted. In Exp. 1, liquid swine manure (LSM) was applied in fall or spring for two site years (A, B). In Exp. 2, LSM was zone-applied either all preplant (PP) or split between preplant and sidedress (SP) for three site years (C, D, E). In both experiments, dietrich (DMI), vibro shank (VS), or subsurface deposition (SSD) applied the LSM, corn (Zea mays L.) was seeded in the manured zone, and NO3–N movement was monitored. Nutrients were supplied by inorganic fertilizer (IF) in control treatments under conventional till (CT), no till (NT), and zone till (ZT). With fall-applied LSM, after a mild winter, more N was lost from the soil–plant system (i.e., 35 kg ha–1 soil NO3–N) than after a cold winter with snow cover (18 kg ha–1), and corn grain yield was reduced (by 1.2 Mg ha–1), even though supplemental fertilizer N was sidedressed. In Exp. 2, with LSM zoned all PP or SP, grain yield and N use efficiency were comparable to that with IF, except when double the crop N requirement was zoned all PP (Site D). Planting into a zone of concentrated LSM (3.4 S m–1) reduced grain yield when the LSM was injected by VS. With careful management, zonejection allows efficient utilization of manure nutrients while preserving residue cover.