EVAPORATION FROM SOIL INFLUENCED BY CROP SHADING, CROP RESIDUE, AND WETTING REGIME

ABSTRACT Soil evaporation (E) was measured with mini-lysimeters 225 mm deep and 150 mm in diameter over the growing season in 1986 and 1987. Mini-lysimeters were placed in com field plots under dryland, limited irrigation and full irrigation water regimes, with or without canopy shading and with or without straw mulch. Soil water content in the mini-lysimeters was periodically matched to that in the surrounding field. Mean daily E was calculated and the effects of canopy shading and straw mulch were analyzed. No significant differences in E between mini-lysimeters at different row positions under the corn canopy were observed. Shading by the corn canopy significantly reduced E 0.3 to 0.5 mm d-i under dryland, 0.6 to 0.7 mm d-i under limited irrigation, and 1.2 mm d-i under full irrigation. The presence of a straw mulch significantly reduced E 0 to 0.1 mm d-l under dryland, 0.5 mm d-i under limited irrigation, and 0.9 to 1.1 mm d-i under full irrigation. The crop canopy played a more important role in reducing soil E than straw mulch under dryland. Under limited or full irrigation the crop canopy and straw mulch contributed equally to E reduction. Combined reduction of mean daily E by the crop canopy and straw mulch was approximately 0.5, 1.0, and 2.0 mm d-l for dryland, limited irrigation, and full irrigation wetting frequencies, respectively. KEYWORDS. Soil evaporation, Lysimeters.