GRASSLAND CONVERTED TO CROPLAND - SOIL-CONDITIONS AND SORGHUM YIELD

An appropriate tillage system is needed for conversion of virgin lands or revegetated lands to croplands to ensure sustainable crop production. We compared the effects of three tillage systems (viz. primary tillage with sweep implement (SW), moldboard plough (MB), and no-tillage NT)) on grain sorghum (Sorghum bicolor (L.) Moench) yield and some soil properties. The land had been used for growing mainly Blue grama grass (Bouteloua gracilis) and Buffalograss (Buchloe dactyloides) for over 50 years. A split-plot field experiment with SW, MB, and NT as main plots was conducted on a Pullman clay loam (Torrertic Paleustolls). Sub-plot treatments were (a) increased soil water content at planting by adding 114 mm of water (PW+), and (b) existing soil water content at planting (PW-). Because of the surface mulch, more soil water was stored in the NT treatment than in either the SW or MB treatments. The increased stored water was also reflected in greater grain and stover yields for NT sorghum. Peak water extracted from soil by crop, as estimated from soil water content measurements, occurred during the vegetative stage at 60 days after emergence (DAE). It was greatest for NT sorghum, followed in order by SW and MB. Although grain and stover yields were larger with NT than with SW or MB, grain and stover from MB plots contained more nitrogen than those from SW and NT plots. Soil organic carbon content at a depth of 0-15 cm was significantly greater (P < 0.05) under NT (1.40%) than under SW (1.21%) or MB (1.25%). Ploughing increased soil nitrogen mineralization, with the result that NO3--N at a depth of 0-15 cm was larger under MB than under NT. The NH4+-N content under the three tillage systems was highly variable. From a production viewpoint, a no-tillage system is better than MB or SW for converting revegetated land to cropland in locations where soil water is limiting.