Abstract

Nitrate leaching to ground and surface water is an increasing concern in agriculture. A ridge-tillage configuration, with placement of nitrate nitrogen (NO₃^--N) or its source in the elevated portion of the ridge, can potentially isolate fertilizer from downward water flow and minimize nitrate leaching. In the experiment, the simultaneous distribution of water, nitrate, and ammonium under three ridge widths was measured using the gravimetric method. Monitoring of the water movement revealed that vertical water movement was much greater than horizontal movement. Compared with 30 and 90 cm ridge width, soil water content at 60 cm ridge width could better meet crop water requirement and relatively decreased irrigation volume. The distribution of NO₃^--N in the soil was similar to distribution patterns of water, while ammonium distribution measurements indicated that there existed an extremely high ammonium concentration in the furrow for ridge-furrow system. These results support the conclusion that water infiltrated in furrows and primarily moved laterally to ridge positions, minimizing downward water movement under the ridge. In this experiment, we recommend that the suitable ridge width for ridge tillage management should be within the range of 60 to 75 cm.

Key words: Ridge tillage, ridge width, wetted front, soil water content, nitrate-nitrogen distribution, ammonium distribution.