Re-utilization of Chinese medicinal herbal residues improved soil fertility and maintained maize yield under chemical fertilizer reduction

Excessive utilization of chemical fertilizers (CF) is not a sustainable agricultural development strategy due to adverse effects on soil health. In contrast, a combination of organic and mineral fertilizers has a positive effect on both soil health and productivity. Chinese medicinal herbal residues (CMHR) is the plant material wastes remaining after drug extraction but has not been extensively used as fertilizer. We evaluated application of CMHR to maize fields over 3 consecutive growing seasons in the presence and absence of standard CF to assess improvements in soil fertility, maize yields and sustainable development. CMHR fertilization increased soil organic matter and total N and K when mixed with chemical fertilizer at 50 and 75% the standard application rate. Soil organic matter increased by 27.0–51.4% and available –N, -P and -K levels and grain yields as well as N and P use efficiency in the presence of CMHR mixes were similar to levels obtained with chemical fertilizer only. These increases in production were due to increased leaf areas, photosynthetic rates, grain number and 1000-grain weights. The addition of CMHR to fields posed a slightly risk of toxic-metal pollution. Overall, we found that (1) CMHR can be used as an effective organic fertilizer and replace up to 50% of the amount of chemical fertilizer normally applied to fields without hampering maize grain yields and (2) CMHR application to agricultural fields is an effective recycling strategy and nutrient management practice to improve soil fertility under CF usage reduction.