To study the effect of pyrolysis temperature and residence time on properties and nutrient values, biochars were produced from corn stalk, rice hull, peanut hull and tobacco stalk at 200 degrees C-700 degrees C for one minute and 60 minutes, respectively. When temperatures and residence times increase, yields of biochars decrease accompany with higher pH values of biochars, changing the acidity of biochars from acidic to alkaline, and increasing total C and parts of the available N and K contents of biochars. These results indicate that feedstock and preparation technology are important factors affecting available nutrients of biochars.