The response of manured forage maize to starter phosphorus fertilizer on chalkland soils in southern England

The impact of various starter phosphorus (P) fertilizers on the growth, nut rient uptake and dry-matter (DM) yield of forage maize (Zea mais) continuou sly cropped on the same area and receiving annual, pre-sowing, broadcast dr essings of liquid and semi-solid dairy manures was investigated in two repl icated plot experiments and in whole-field comparisons in the UK. In Experi ment 1 on a shallow calcareous soil (27 mg l(-1) Olsen-extractable P) in 19 96, placement of starter P fertilizer (17 or 32 kg ha(-1)) did not benefit crop growth or significantly (P > 0.05) increase DM yield at harvest. Howev er, in Experiment 2 on a deeper non-calcareous soil (41 mg l(-1) Olsen-extr actable P) in 1997, placement of starter P fertilizer (19 or 41 kg P ha(-1) ), either applied alone or in combination with starter N fertilizer (10 or 25 kg N ha(-1)), significantly increased early crop growth (P < 0.01) and D M yield at harvest by 1.3 t ha(-1) (P < 0.05) compared with a control witho ut starter N or P fertilizer. Placement of starter N fertilizer alone did n ot benefit early crop growth, but gave similar yields as P, or N and P, fer tilizer treatments at harvest. Large treatment differences in N and P uptak e by mid-August had disappeared by harvest. In field comparisons over the 4 -year period 1994-97, the addition of starter P fertilizer increased field cumulative surplus P by over 70%, but without significantly (P > 0.05) incr easing DM yield, or nutrient (N and P) uptake, compared with fields that di d not receive starter P fertilizer. The results emphasized the extremely lo w efficiency with which starter P fertilizers are utilized by forage maize and the need to budget manure and fertilizer P inputs more precisely in ord er to avoid excessive soil P accumulation and the consequent increased risk of P transfer to water causing eutrophication.