Relationship between ammonium nitrogen in soil solution and tiller number at early growth stage of rice

Abstract

Exchangeable NH₄ ⁺-N in paddy soils is adsorbed onto cation exchange sites in the soil or present in the soil solution. Although numerous researchers have reported the existence of a relationship between the amount of exchangeable NH₄ ⁺-N in soil and rice growth, differences in the tiller number and the amount of N in rice among different fields cannot be explained by the amount of exchangeable NH₄ ⁺-N in soils. On the other hand, it has been shown in pot experiments that higher amounts of NH₄ ⁺-N in the soil solution led to a higher tiller number and a larger amount of N in rice. However, little information is available on the relationship between the amount of NH₄ ⁺-N in the soil solution and tiller number under different field conditions. The objective of this study was to clarify the relationship between the amount of NH₄ ⁺-N in the soil solution and the tiller number in different farm fields. The results obtained were as follows: 1) The relationship between the amount of NH₄ ⁺-N in the soil solution and the tiller number at 20 d after transplanting (DAT) was positive and could be represented by a linear equation. 2) There was no relationship between the soil CEC and tiller number at 20 DAT. No significant relationship between the soil CEC and the amount of NH₄ ⁺-N in the soil solution was detected. 3) The amount of positive charges in the soil derived from Fe2+ was approximately 4.0-40.8 cmol( +) kg⁻¹ dry soil, and that of NH₄ ⁺-N was approximately 0.15-0.82 cmol( +) kg⁻¹ dry soil at 20 DAT, suggesting that ferrous iron occupied the cation adsorption sites in soil, resulting in an increase in the amount of NH₄ ⁺-N in the soil solution.