Plant and Soil 173: 55-65, 1995. (~) 1995 Kluwer Academic Publishers. Printed in the Netherlands. Sorghum, wheat and soybean production as affected by long-term tillage, crop sequence and N fertilization A.J. Franzluebbers,EM. Hons and V.A. Saladino Texas Agricultural Experiment Station, Department of Soil and Crop Sciences, Texas A and M University, College Station, TX 77843-2474, USA Received 23 August 1994. Accepted in revised form 23 December 1994 Key words: crop residue quality, crop sequence, nitrogen fertilization, resource efficiency, soil productivity, tillage Abstract Yield decline of cereals grown in monoculture may be alleviated with alternative crop management strategies. Crop rotation and optimized tillage and fertilizer management can contribute to more sustainable food and fiber production in the long-term by increasing diversity, maintaining soil organic matter (SOM), and reducing adverse effects of excessive N application on water quality. We investigated the effects of crop sequence, tillage, and N fertilization on long-term grain production on an alluvial, silty clay loam soil in southcentral Texas. Crop sequences consisted of monoculture sorghum (Sorghum bicolor (L.) Moench,) wheat (Triticum aestivum L.), and soybean (Glycine max (L.) Merr), wheat/soybean double-crop, and rotation of sorghum with wheat/soybean. Grain yields tended to be lower with no tillage (NT) than with conventional tillage (CT) early in the study and became more similar after 11 years. Nitrogen fertilizer required to produce 95% of maximum sorghum yield was similar for monoculture and rotation upon initiation of the experiment and averaged 16 and 11 mg N g-l grain with NT and CT, respectively. After 11 years, however, the N fertilizer requirement became similar for both tillage regimes, but was greater in monoculture (17 mg N g-1 grain) than in rotation (12 mg N g-l grain). Crop sequences with double-cropping resulted in greater land use efficiency because similar or lower amounts of N fertilizer were required to produce equivalent grain than with less intensive monoculture systems. These more intensive crop sequences produced more stover with higher N quality primarily due to the inclusion of soybean in the rotation. Large quantities of stover that remained on the soil surface with NT led to greater SOM content, which increased the internal cycling of nutrients in this soil. In southcentral Texas, where rainfall averages nearly 1000 mm yr -1 , more intensive cropping of sorghum, wheat, and soybean with moderate N fertilization using reduced tillage can increase grain production and potentially decrease N losses to the environment by cycling more N into the crop-SOM system. Introduction Yield decline of cereals grown in monoculture decreas- es returns on investments, resulting in reduced prof- it and poor resource use efficiency (Power, 1990). Rotation of cereals with legumes can alleviate this yield decline by providing additional N to the cereal crop through legume residue decomposition (Baldock and Musgrave, 1980) and/or by altering the physi- cal, chemical, and biological environment of the soil which affects cereal root development (Roder et al., 1989) and plant vigor (Cook, 1984; Copeland and Crookston, 1992). The contribution of additional N to the cereal has been termed a "N effect", where- as yield benefit beyond that accounted for by N has been termed a "rotation effect". Barber (1972) con- cluded that the rotation effect was due to improved physical condition (i.e. porosity and aggregation) of the soil after the growth of an alfalfa (Medicago sati- va L.)/grass mixture. In contrast, however, Fahad et al. (1982) found reduced soil aggregation and porosity after soybean compared to corn (Zea mays L.). Biolog- ical factors that may contribute to the rotation effect with increased crop diversity include a reduction in