The combination of continuous cereal cropping, tillage and stubble removal reduces soil fertility and increases soil erosion on sloping land. The objective of the present study was to assessment soil fertility changes under stubble removal and stubble retention in the Loess Plateau where soil is prone to severe erosion. It was indicated that soil N increased a lot for and two stubble retention treatments had the higher N balance at the end of two rotations. Soil K balance performed that soil K was in deficient for all treatments and two stubble retention treatments had lower deficit K. The treatments with stubble retention produced higher grain yields than the stubble removal treatments. It was concluded that stubble retention should be conducted to increase crops productivity, improve soil fertility as well as agriculture sustainability in the Loess plateau, China.

A study of the formation of gouging pits in Mn7CrZ steel zinder impact abrasizie wear conditions was conducted using theories of elastic impact and contact, analysis of photoelasticity, and scanning electron microscopy (SEM). The results show that the maximum shear stress occurs at z = 0.48~1, and this initiates a crack; the crack propagates at an angle of 45" from the horizontal; and the gouging pit is conical. The SEM observations are in agreement with the theoretical calculations.