Abstract: During 2010-2011, 10 field trials were conducted with 6 main cropping systems to study the potassium input, output and balance in Hubei Province. The results showed that the annual average rates of K input to the agroecosystems by fertilization, rainfall, irrigation and straw return were 129.8, 10.3, 14.9 and 30.1 kg·hm^-2, respectively. It indicated that rainfall, irrigation and straw return played an important role in soil K input. Potassium outputs from soils by harvest and runoff were 211.2 and 26.4 kg·hm^-2, accounting for 88.5% and 11.5% of total K output, respectively. The rate of K removed by straw was 186.3 kg·hm^-2, accounting for 89.1% of total harvest. However, only 16.2% of that was returned to the field. This suggested that a large proportion of K was carried off by straw from the agroecosystems. In other words, the potential of input K by straw return to field is huge. Soil K is deficit in the main cropping systems in Hubei with an average of -52.4 kg·hm^-2. Therefore, to improve the K balance in the agroecosystems of Hubei, it is practical to increase K fertilization, through promoting the K input through rainfall and irrigation, and the return of straw to the field.

Key words: soil respiration, carbon flux estimation, sampling strategy, region division