Distribution of organic carbon and inorganic nitrogen in a soil under various tillage and crop sequences

ABSTRACT:

The interaction of various tillage and crop sequences on the distribution of soil organic carbon (C) and inorganic nitrogen (N) is important for predicting changes in soil physical and chemical properties and potential environmental impacts of soil and crop management. This study was conducted to determine the distribution of organic C, nitrate (NO₃-N) and ammonium (NH₄-N) in a soil with various tillage methods and crop sequences. A tillage experiment was started in 1978 with treatments of chisel, disk, no-till, plow, ridge-till, and sub-soil. In 1985, each tillage plot was divided into two subplots to which two crop sequences of continuous corn [Zea mays L.] (C-C), and soybean [Glycine max (L.) Merr.]-corn (S-C) were assigned. Nitrogen fertilizer was applied at a rate of 100 kg N ha⁻¹ y⁻¹ when plots were planted to corn. In the spring and autumn of 1989, soil samples were taken from crop sequences and tillage plots to a depth of 1.5 m in 0.3 m increments for determination of NOTN, and NH₄-N contents. Soil samples were also collected from 0–10, 10–20, 20–40, 40–60, 60–80, 80–100, 100–150, 150–200, 200–250, and 250–300 mm soil depths for organic C determination. Multivariate analysis of variance (MANOVA) was used to analyze the data taken from different soil depths. Organic C concentration was greatest at 0–10 mm soil and decreased with increasing soil depth. Organic C was greatest for no-till and was least for sub-soil. Greater residue in C-C was associated with greater soil organic C than S-C. Organic C quantity (kg ha⁻¹ 300 mm⁻¹) followed the same trend as organic C concentration. The plow treatment had the greatest NOTN quantity in the 0–0.3 m soil depth. All tillage systems had similar NO₃-N amounts in deeper soil. NH₈-N content of soil was not influenced by tillage or crop sequences. Soil organic C was related to both the amount of residue produced and left on the soil surface after harvest and also to the degree of soil surface disturbance. Nitrate-N was affected more by tillage and crop sequence systems than was ammonium-N.