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We studied the effects of the long-term (17 years) application of different chemical fertilizer regimes on soil N and its inorganic fractions in relation to the soil physical properties in a sloping cropland in the hilly Loess Plateau. Seven treatments comprised of two factors were arranged within a randomized complete block design. As expected, crop yield increased 2-4-fold, but soil structure did not degrade. Under long-term fertilization, the portion of the small aggregates (<2 mm) and sand content were significantly decreased while the large aggregates (>2 mm) and the silt content increased by 276% and 7.4%, respectively, as compared with those in areas without fertilization. Moreover, the various continuous chemical fertilization treatments increased SOC content by 12.9% and total N by 12.4%, on average, compared with unfertilized plots. The SOC, total N, and shoot C, shoot N had close relationships with the large aggregates (>2 mm) and the clay content. The results suggest that, in this setting, the long-term addition of both N and P may sustain soil quality of an infertile sloping cropland in this region, compared to agriculture without fertilizer or applications of N alone. [ABSTRACT FROM AUTHOR]

[Objective] The research aimed to study change characteristics and formation cause of summer precipitation abnormality in Loess Plateau of northern Shaanxi Province. [Method] Based on summer precipitation data at 15 observation stations in Loess Plateau of northern Shaanxi Province and NCEP/NCAR dataset from 1961 to 2008, change characteristics of summer precipitation in the region were investigated by using linear trend estimation and composite analysis. [Result] Summer rainfall had decrease trend in most parts of northern Shaanxi Province, but had increase trend in western and southern regions. The interannual and interdecadal variations were obvious. It had a large amount of precipitation from the mid-1970s to the mid-1990s, while summer rainfall had decrease trend after the mid-1990s and increase trend in recent years. In wet years, it was a large positive anomaly zone from western Ural Mountains to northern Lake Baikal at middle and high latitudes, indicating that there was a blocking high over the Ural Mountains, while it was negative anomaly zone from northern Okhotsk Sea to Lake Baikal. From Northwest Pacific Ocean to Bohai Sea Bay and North China, it was a wide range of significant positive anomaly zone, which was favorable for Western Pacific subtropical high extending westward and northward. The analysis in dry years showed opposite circulation configuration. It was "-, +, -" wave train distribution in middle and high latitudes and positive anomaly zone along the Sea of Okhotsk. Western Pacific subtropical high was also by south and east. Major water vapor was from southeast direction in wet years, and abundant water vapor caused more summer rainfall in northern Shaanxi. In dry years, water vapor was from westerly turning southerly flow. It was weaker and by east. [Conclusion] The research provided reference for reasonable utilization of summer precipitation in the zone. [ABSTRACT FROM AUTHOR]

Agricultural management practices play an important role in soil structure and fertility. However, there is a lack of knowledge on the effects of long-term fertilization on aggregate structure in the Loess Plateau region in China. This study was devoted to examining the responses of soil aggregate stability and associated structure to fertilizers over 19 years under a soybean (Glycine max L.)-corn (Zea Mays) rotation. Treatments included unfertilized control (CK); nitrogen (N), phosphorus (P), and NP chemical fertilizers; and manure (M) and MN, MP and MNP organic/chemical combinations. The results showed that the water-stable aggregates, mean weight diameter, geometric mean diameter, aggregate state, and aggregate degree decreased in chemical fertilizers (N, P, and NP). However, it increased in all treatments containing manure (M, MN, MP, and MNP) compared to the CK. The changes in dispersion rate and fractal dimension were opposite to those indicators in all treatments. The applications of chemical fertilizers do guarantee an increase in crop yield, but only organic fertilizers significantly improved soil structure. These results suggest that manure's incorporation into loessial soil is a preferred strategy for sustainable soil management. [ABSTRACT FROM AUTHOR]