The relationship between soil N, organic matter and N uptaken by crops on dryland

Six arable soils with different fertility in Yongshou county, Shaanx Province with typical semiarid-climate characters were chosen. Soils were sampled at different depth within 0-100 cm before sowing. The content of mineralizable nitrogen (MAN), total nitrogen (TN) and organic matter (OM) at different depth of soils were analysed to study the relationships between these three indices and crop uptake of nitrogen (CUN). The results showed that there were good correlations among MAN, TN and OM in different soil layers. The correlation between MAN and CUN was higher than that between MAN and TN, as well as MAN and OM. The correlation coefficient between the sum of MAN plus initial mineral nitrogen in soils and CUN was higher than that between MAN and CUN. MAN, TN and OM had higher correlation to CUN at the depth of 0-45 cm than that at the depth below 45 cm, and the correlation was the highest at the depth of 30-45 cm. As an index to evaluate soil nitrogen availability, MAN was better than TN or OM (or modified value).