Comparison of potassium quantity-intensity relationships in tropical paddy soil under tillage and no-tillage systems after fifteen growing seasons

The information on the behaviour of potassium (K+) in tropical paddy rice soils, which is important for a better understanding of the plant availability of K+ is still very limited. We compared the quantity-intensity (Q/I) relationships for K+ under conventional tillage and no-tillage systems in tropical paddy fields in the absence and pre sence of K+ fertiliser in the addition of nitrogen. The results showed that the values of the activity ratio for K (ARK) and potential buffering capacities (PBCK) in the no-tillage rice field were respectively 16% and 33% higher than that in the conventional tillage field. With the addition of K fertiliser, the value of exchangeable K in equilibrium (ΔK0) in the no-tillage paddy field was 67.9% greater than that in the conventional tillage field. This indicates that K fertilisa tion is more efficient when applied on a no-tillage paddy field. When the K fertiliser was added (49.8 kg K/ha), the application of N fertiliser at the rate of 115 and 184 kg N/ha resulted in a higher ARK value than that at the rate of 46 kg N/ha. This suggests that the simultaneous application of K and N fertiliser was able to increase exchangeable K in the soil. The application of no-tillage increased of the dry grain yield of rice (about 10%) compared with the application of conventional tillage. Meanwhile, there were significant relationships between the rice yield with the ARK and ΔK0. Moreover, the ARK was significantly correlated with K-uptake