Starter phosphorus and broadcast nutrients on corn with contrasting colonization by mycorrhizae

Early P nutrition in corn (Zea mays L.) is important for early growth and arbuscular mycorrhizal fungi (AMF) may help juvenile corn plants access soil P. The role of AMF colonization in manured soils and the impact of AMF on the need for starter P is not well known. This study was designed to assess the response of corn with contrasting levels of AMF colonization to low rates of starter P under inputs of broadcast liquid dairy manure or N and P fertilizer. The study was conducted on a high-P-testing soil in south-coastal British Columbia. Contrasting AMF colonization was achieved by growing corn either after corn or after fallow. Both AMF colonization and starter P improve early growth and, to a lesser extent, final harvest even on a relatively high P soil receiving a heavy application of P as broadcast liquid dairy manure or fertilizer. The effects of AMF colonization and starter P were additive, so both contribute to maximum yield. Our study suggests that practices favoring AMF colonization will help juvenile corn plants take up P. While strategically placed low rates of starter P were beneficial for juvenile plants, these treatments were less effective than conventional sidebanding at 30 kg P ha(-1) because the effect did not carry forward to final harvest, even in corn that was well colonized by AMF. Therefore, better nutrient strategies and AMF colonization are needed to ensure that corn crops will gain sufficient P with minimum starter mineral fertilizer on manured soils.