How long-term chemical fertilization of sloping cropland enhances yield and fertility without compromising coil structure

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.