Availability of Phosphorus after Long‐term Whole and Separated Slurry Application to Perennial Grass prior to Corn Silage

Removing solids from whole dairy slurry (WS) can reduce P loading on fields. This study investigated the effects of 11 yr of applications of WS, separated liquid fraction (LF), commercial fertilizer, WS plus fertilizer, and a control on total and extractable (Kelowna) soil P in perennial grass ( Festuca arundinacea Schreb.) and two subsequent silage corn ( Zea mays L.) crops. Plots received 200 kg N ha −1 with or without 40 kg P ha −1 . Shoot biomass, P uptake, arbuscular mycorrhizal fungi root colonization, and soil microbial P were determined for corn at six leaves. Whole‐crop and grain yield, P uptake, dry matter, and grain content were determined at maturity. The LF treatment received 30% less manure P than WS, had lower extractable soil P at 0 to 15 and 15 to 30 cm, and had lower total P at 0 to 15 cm. Historical treatments had no effect on soil microbial P or arbuscular mycorrhizal fungi colonization. At six leaves, corn shoot biomass, P concentration, and P uptake were related to historical P rates in Year 2, but the relationship was not apparent in Year 1. Starter P fertilizer increased shoot yield and P uptake for all treatments in both years. At maturity, most yield parameters for WS and LF were similar in Year 1, but in Year 2, there was a significant response to starter P fertilizer and a positive relationship between historical P rate and corn performance. This study shows that long‐term LF treatments reduced the risk of P pollution with relatively little effect on the P response of subsequent corn crops. Core Ideas Historical N‐based LF treatments had lower P surplus and soil P than WS. Long‐term WS and LF treatments had no effect on AMF and soil microbial P. Juvenile corn responds to starter P in high‐P‐testing soils. The residual effects of long‐term LF on subsequent corn were small. Use of LF may help reduce soil P accumulation on dairy farm soils.