Tillage and liming effects on crop and labile soil nitrogen in an acid soil

Limited information is available on soil management effects on crop production and nitrogen (N) cycling in acid soils. The effects of conventional tillage (CT) versus no-till (NT) and liming (0 versus 7.5 Mg ha−1), and their interaction, on labile N pools in an acid soil were evaluated during the 7th to 10th year of a 3-course small grain rotation. Crop production and N uptake, N2 fixation by pea (Pisum sativum L.), and labile soil N were determined. Liming increased the pH from 5.3 to 6.0 in the top 10 cm of soil and had no influence below 10 cm depth. No-till increased average crop yield and N uptake by 12 and 14%, respectively, compared to CT. The corresponding increases due to lime application were 13 and 20%. There was no treatment effect on N concentrations in plant tissues (probably because of adequate N fertilizer application), or on N2 fixation in pea. The percent N derived from the atmosphere varied from 12% in one dry year to 68% in a moister year. Soil NO3 in spring and autumn was significantly higher where the preceding crop was field pea, particularly in the surface soil layer. Soil inorganic N was little influenced by tillage and liming. In contrast, soil microbial biomass N concentration was consistently greater with liming than without (30-64% difference) and with NT than with CT (7-36% difference), but little affected by crop sequence. Liming enhanced the positive effect of NT on soil microbial biomass N. Crop total N uptake was significantly correlated with microbial biomass N (r=0.69∗ for barley (Hordeum vulgare L.), and 0.70∗∗ for canola (Brassica rapa L.)). Liming with NT can be effective in increasing N turnover and crop growth in acid soils.