Broadcast and residual P versus annual seed-placed P

Abstract

The yield and nutrient uptake effects of single broadcast P treatments, annual seed-placed P treatments and their combination, were studied over five years. Maximum yield was attained from a combination of moderate levels of seed-placed and broadcast P applications. Moderate broadcast treatments (40 kg P/ha) alone produced a five-year average yield which closely approached the yield from large annual seed-placed treatments ( 20 kg P/ha/year), while larger residual treatments exceeded it. The Zn concentration in plants on plots receiving 160 kg P/ha was significantly reduced and approached levels considered deficient. After the production of five wheat crops on plots which received the broadcast application of 160 kg P/ha, the distribution of the remaining fertilizer residues among various soil P fractions was: resin-P, 35 %; NaOH-P, 30-40 %; NaHCO3-P, 15 %; HCl-P, 0-5 %; H2SO4-P, 5 %; aggregate-protected P, 5 %. Half the fertilizer residues remained in plant available forms (resin-P, NaHCO3-P).