Abstract
Concentrations of NH‐N and NO‐N in the surface (0–6 in.) layer of a light soil, with and without added nitrogen fertiliser, were measured from May to October 1957 on plots kept free of vegetation and those cropped with ryegrass.
The application of nitrogen fertilisers to the soil increased the concentration of mineral nitrogen in the surface layer. On bare land the level of mineral nitrogen in the surface soil remained high until July when it was reduced by heavy and prolonged rain. NH‐N from ammonium sulphate or urea was converted to NO‐N slowly; 20 weeks were required to nitrify ail the added nitrogen.
When established, ryegrass removed nitrate very rapidly from the soil and reduced the level of NO‐N to < 1 p.p.m. both on plots with or without fertiliser‐N. On plots dressed with ammonium sulphate there was a loss of NH‐N under ryegrass and no corresponding increase in NO‐N. The first cut of grass taken in July contained three‐quarters of the nitrogen applied as fertiliser; the second cut contained only one‐tenth of the amount applied.
Examination of soil samples taken in October from depths up to 3 ft. showed no accumulation of mineral nitrogen under ryegrass, but there was a downward movement of nitrate from uncropped soil.