Cropping systems are thought to alter soil quality in paddy rice fields. This study was conducted to quantify the long-term effects of continuous crop production under different cropping systems with different crop rotations on physical properties of alluvial clay soil in the Mekong Delta, Vietnam. Soil samples were collected from four treatments: (i) traditional intensive rice monoculture with three rice crops per year (R-R-R); (ii) rotation with two rice crops and maize (R-M-R); (iii) rotation with two rice crops and mung bean (R-Mb-R); and (iv) rotation with one rice and two upland crops, mung bean and maize (R-Mb-M). We hypothesized that cropping systems with rotations of upland crops and their temporary beds improve the physical quality of paddy rice soil; hence, they are better options towards sustainable agriculture. Results show an improvement of soil physical quality for systems with two rice crops and one upland crop (R-M-R and R-Mb-R) and those with one rice crop with two upland crops (R-Mb-M) compared with intensive rice monoculture (R-R-R). This was translated in decreased bulk density and soil strength, increased soil organic carbon and total porosity, and higher aggregate stability index, plant-available water capacity, and Dexter's S index, especially at depths of 10-20 and 20-30 cm. The systems with different upland crops (maize or mung bean) showed similar high physical quality improvement. To maintain soil quality in future seasons, introducing a cropping system with at least one upland crop in rotation with rice is recommended.

In the Mekong Delta, alluvial clay soils have been used intensively over many generations for rice monoculture. Currently, farmers are confronted by problems of declining land productivity. Rotations comprising rice and upland crops can increase soil quality, but appropriate cropping systems for paddy soils have received relatively little attention. We therefore established a multiyear field experiment to evaluate the long-term effects of cropping systems with different rotations on soil chemical quality. Systems laid out in a randomized complete block design with four replications were as follows: (i) traditional rice monoculture with three rice crops per year (R-R-R), (ii) rotation with two rice crops and maize (R-M-R), (iii) rotation with two rice crops and mung bean (R-Mb-R) and (iv) rotation with one rice crop and two upland crops – mung bean and maize (R-Mb-M). We hypothesized that systems with rotations of upland crops and their temporary beds improve chemical quality of paddy rice soil. Soil chemical parameters were determined to better understand and evaluate the sustainability of the cropping systems. Results showed an improvement in soil chemical quality for cropping systems with rotations of rice and mung bean or maize grown on temporary beds (R-M-R, R-Mb-R and R-Mb-M), particularly the content of soil organic carbon and a presumed hydrolysable labile carbon fraction compared with rice monoculture. Less pronounced improvements in EC, CEC and total acidity were also found with inclusion of upland crops. Cropping systems of rice with upland crops improved rice grain and straw yield in subsequent season in contrast with rice monoculture