Impact of continuous nine-year application of biochar on potassium supplying capacity of the soil.

Introduction: Straw biochar can significantly increase the content of available potassium (K) in soil, whereas its regulatory effect on soil K supply capacity remains unclear and lacks long-term field verification. To clarify the response mechanism of soil K supply capacity to long-term straw biochar amendment, a 9-year continuous field experiment was carried out to explore the improvement effect of straw biochar on soil K supply characteristics and K uptake by maize. Methods: This study was conducted based on a long-term field experiment in Shenyang Agricultural University under a humid and sub-humid monsoon climate, with Haplic Luvisols as the tested soil. After 9 consecutive maize growing seasons, soil samples at the 0-20 cm depth were collected. A two-factor randomized block design was set up with four treatments, including B0K0 (no biochar and no K fertilizer), B0K1 (K fertilizer only), B1K0 (biochar only), and B1K1 (biochar with K fertilizer). Results: 9 consecutive years of straw biochar application significantly increased illite content. Compared to B Discussion: These variations induced by biochar application effectively alleviated the negative K balance of farmland soil, comprehensively improved soil K supply capacity, and facilitated K uptake and utilization of maize, which further promoted the accumulation of plant dry matter. This long-term field study confirms that the combined application of straw biochar and K fertilizer is an effective measure to improve soil K availability, which provides reliable scientific basis for K nutrient regulation in farmland soil.