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An understanding of long-term tillage and straw management impact on soil structure and productivity is necessary for the further development of conservation tillage practice in dryland farming areas. Data from a 15-year field experiment conducted in Shanxi, on the loess plateau of northern China, were used to compare the long-term effects of no-till and residue cover (NTSC) with conventional tillage (CT) in a winter wheat (Triticum aestivum L.) monoculture. Long-term CT and straw removal resulted in poor soil structure and low productivity. Mean soil bulk density in NTSC was 1.5% less than in CT and capillary porosity (2 mm was much greater for NTSC in the 0-0.20 m profile. Soil organic matter and total N and P were 27.9%, 25.6%, and 4.4% greater in NTSC, respectively, and earthworms (19/[m.sup.2]) were found only in the no tillage treatment. Crop yield and water use efficiency tended to be higher under NTSC than under CT, especially in the years of low rainfall, suggesting that the change in soil structure has provided a better environment for crop development. Our 15-year experimental data indicate that NTSC is a more sustainable farming system, which can improve soil structure, and increase productivity with positive environmental impacts in the rainfed dryland farming areas of northern China. Additional keywords: conservation tillage, dryland farming, wheat, aggregate stability, soil porosity, soil fertility, yield, water use efficiency., Introduction China is one of the world's major dryland farming countries. Rainfed land (crop production without irrigation) is largely located in the 16 provinces of northern China, where 33 Mha [...]

A good understanding of how the target environments for a breeding program differentiate the germplasm with respect to yield is crucial and allows plant breeders to better target their germplasm. To determine the relationships among high rainfall yield testing locations, yield data from 8 yr of CIMMYT's High Rainfall Wheat Yield Trial (HRWYT) were analyzed by shifted multiplicative model (SHMM) and incremental sum of squares (ISS) classification analyses to group sites within and across years. In the cumulative cluster analysis, about half of the sites clustered into a group characterized by increasing temperature toward maturity. The SHMM analysis identified several sites with high overall association with other sites around the world, and which can be considered as good predictors of global yield performance within the high rainfall megaenvironment. These are autumn-sown locations, which fall into the biggest group of the cumulative cluster analysis with increasing temperature during the growing season. On the other hand, remarkably low associations with global yield ranking were shown for Sta. Catalina (Ecuador) and CIMMYT's primary high rainfall yield-testing location at Toluca (Mexico), which in contrast experience decreasing temperatures toward maturity. Although excellent sites for disease screening, this analysis shows that they do not associate well with the world's high rainfall wheat growing areas for yield., THE BREAD WHEAT BREEDING PROGRAM of the International Maize and Wheat Improvement Center (CIMMYT) breeds spring wheat lines for all major wheat growing areas in the developing world (Rajaram and [...]