Abstract: To explore the effects of biochar aging on soil moisture and fertility in cropland, we set up a field twofactor randomized block experiment. There were two kinds of biochar with different aging time (newly applied biochar to the soil, Y₁; biochar for the 5th year of natural aging in the field, Y₅) along with three doses of biochar application (0 t·hm^-2, C₀; 6 t·hm^-2, C₆; 12 t·hm^-2, C₁₂).  We investigated the effects of those two different types of biochar on maize yield, water content and fertility in different soil layers. Results showed that under the same dose of biochar application, the positive effects of biochar with the 5th year of aging on maize yield, soil moisture and fertility were lower than that of fresh biochar addition. The maximum increment (28.3%) of maize yield was observed under Y₁C₁₂ and the minimum increment (6.9%) under Y₅C₆. The positive effect of biochar in the 5th year of aging on yield was less than that of fresh biochar under the same application dose. Except the Y₅C₆ treatment, biochar addition significantly improved water use efficiency of maize compared with the Y₁C₀ (Y₅C₀) treatment (5.4%-16.7%). The effect of biochar application on soil moisture was mainly concentrated in the surface soil. The soil moisture under the aged biochar treatment was significantly lower than that of the fresh biochar treatments. There was no significant difference in soil moisture between the treatment of aged biochar with low dose (Y₅C₆) and the treatment of Y₁C₀ (Y₅C₀). The application of biochar significantly increased the contents of soil nitrate, ammonium, alkaline hydrolysis nitrogen, total nitrogen, available phosphorus, and available potassium, and thus improved the comprehensive soil fertility, and such effects of biochar in the 5th year of aging on soil nutrients were lower than that of fresh biochar. The comprehensive soil fertility of various treatments was in order of Y₁C₁₂>Y₅C₁₂>Y₁C₆>Y₅C₆>Y₁C₀ (Y₅C₀). Our results can provide theoretical foundation for rational utilization of biochar.

Key words: biochar aging, soil moisture, water use efficiency, comprehensive soil fertility.