Injection and nitrification inhibitor improve the recovery of pig slurry ammonium nitrogen in grain crops in Brazil

Efficient management practices are needed for no-till (NT) cropping systems fertilized with pig slurry (PS). We evaluated the effect of application mode (surface broadcasting vs. injection) with or without the nitrification inhibitor dicyandiamide (DCD), on the recovery of PS ammonium nitrogen (NH4–N) in 2-yr crop succession (corn [Zea mays L.]/oat [Avena strigosa L.]/corn/wheat [Triticum aestivum L.]) under NT and irrigation. Each crop received PS at planting. The NH4–N fraction of PS was enriched with 15N to discriminate the contribution of current vs. past applications to crop N uptake. Compared to surface application, injection increased corn uptake of PS NH4–N by 22 kg N ha−1 under low precipitation regime, likely because it efficiently reduced ammonia volatilization; the effect was small under high precipitation regime and in winter crops in general. To the contrary, DCD doubled the uptake of PS NH4–N in corn (+24 kg N ha−1) under high precipitation regime, likely because it reduced losses through N leaching, whereas the gain was smaller under drier conditions and in winter crops in general. Because of this complementary response to injection and DCD, the retention of PS NH4–N in the soil–plant system for the whole crop succession was maximized where PS was injected in combination with DCD, being 19 to 23% greater than injection or DCD alone. The injection of DCD-treated PS is therefore recommended to maximize crop uptake of PS NH4–N and minimize environmental losses under irrigated NT conditions in southern Brazil.