Regression equations to monitor inorganic nitrogen changes in fallow and wheat soils

Soil NH⁺₄-N and NO^?₃-N at five soil depths (0–10, 10–20, 20–40, 40–60, 60–80 cm) and some environmental variables were measured in a field trial under fallow and wheat for 9 months.Significant linear and quadratic relationships were obtained relating soil NH⁺₄-N, NO^?₃-N, NH⁺₄-N + NO^?₃-N, and NH⁺₄-N + NO^?₃ + total-N uptake by wheat to soil heat accumulation (temperature), moisture, and rainfall. R² values generally decreased with soil depth and the maximum value (37%) was obtained for NO^?₃-N changes in the topsoil (0–10 cm).Although a considerable amount of variation in the inorganic values recorded is not included in the equations, our results suggest that the development of the above relationships particularly of the quadratic type are useful to predict crop requirements for N by measurement of environmental variables in the field.