The reserve of soil nutrients is limited.In case of irrational use of land,nutrients would be depleted sooner.Before the 1950s the low grain production in China
<正> INTRODUCTION Nitrogen is a key component of soil organic matter. Only when we have succeeded in characterizing the major part of organic N-containing compo
<正> As early as the 1950s, there had already been reports on the δ 15N value of some chemical fertilizers (Hoering, 1955). Since Kohl and his co-workers (1971