Improving nitrogen and phosphorus response of corn ( Zea mays L . ) to dairy slurry by precision injection : benefits and risks

We evaluated the benefits and risks of precision planting corn near dairy slurry injection furrows (DS-I) in terms of crop performance and environmental impact relative to mineral fertilizer (MF) and broadcast/ incorporated (DS-B) slurry. The study was conducted in 2010-2014 on silty loam in a cool maritime climate in south coastal BC, Canada. Injected manure improved N and P uptake and yield relative to broadcast manure at all application rates. Phosphorous (P) uptake was comparable or better than fertilizer but nitrogen (N) uptake was lower. Apparent N uptake (% of applied N adjusted for control), depending on application rates, was 53-79% for MF, 41-53% for DS-I, 36-42% for DS-B. Crop response to DS-I plus starter (i.e. DSI+S) approached MF for most variables and for P uptake it was higher. DS-I had about two times higher emissions of nitrous oxide (N2O) than DS-B due to greater emission peaks within a month of nutrient application; N2O emissions were slightly higher than IPCC factors for DS-I but substantially lower for DS-B. Movement of nitrate below the root zone had modest peaks after application and after summer drought but unlike N2O continued through the cool rainy season. The study showed that precision injection improves corn performance compared to conventional methods but to reach maximum yield either starter fertilizer or relatively high N manure rates are required.