ABSTRACT

Paddy soils are the dominant source of nitrogen for rice via mineralization, and knowledge about the available nitrogen (AN) in paddy soil is important for rice cultivation. Although the relationship between AN and soil physicochemical parameters has been studied, no systematic studies of the relationships between AN and the soil moisture content of various soil types in Japan have been studied. Therefore, we examined the impacts of soil types and treatment of organic matter application or paddy–upland rotation on these relationships. We sampled topsoils from 30 paddy fields throughout Japan. We compared the relationships between AN and soil physicochemical properties, such as total nitrogen (TN), cation exchange capacity, soil water-holding capacity (WHC), mass water content after harvest (MWH), and water content after harvest (WCH). The scatter diagram revealed that AN and either MWH or WCH (p < 0.01) had the highest positive linear correlation coefficient; the pattern became clearer after separating Andosols and non-Andosols. We analyzed the relationship between AN and either TN or MWH in 100 topsoils, including soils from treatment plots with successive organic matter application or paddy-upland rotation. A significantly positive correlation between AN and TN was observed, although the regression slopes for volcanic or non-volcanic soils differed. The decrease in AN due to frequent paddy–upland rotation was greater than that for TN. On the other hand, a highly positive correlation between AN and MWH was observed, and the coefficient of determination was higher than that for AN and TN. TN and the WHC increased when the accumulation of organic matter in paddy soil was greater. As there was a positive correlation between WHC and MWH, a positive correlation was also observed between AN and MWH. Additionally, we investigated year-to-year variation in MWH using topsoil samples collected before autumn tillage, for 3–5 consecutive years in 24 plots, for various soil types throughout Japan. In order to eliminate the effects of precipitation and to minimize the fluctuation of MWH in paddy topsoil, it was desirable to collect topsoil samples within 24–96 hours of the last precipitation of 1 mm h⁻¹ or more, for the measurement of moisture content.

摘要

稻田土壤是通过矿化作用为水稻提供氮的主要来源，而了解稻田土壤中的有效氮（AN）对水稻种植很重要。虽然已经研究了AN与土壤理化参数的关系，但在日本还没有系统研究过AN与各种土壤类型的土壤含水量之间的关系。因此，我们研究了土壤类型和有机质施用处理或稻田-旱地轮作对这些关系的影响。我们从日本各地的 30 个稻田中采集了表土。我们比较了AN与土壤理化性质之间的关系，如总氮（TN）、阳离子交换能力、土壤持水能力（WHC）、收获后的质量含水量（MWH）和收获后的含水量（WCH）。p< 0.01) 具有最高的正线性相关系数；分离安多溶胶和非安多溶胶后，模式变得更加清晰。我们分析了 100 个表土中 AN 与 TN 或 MWH 之间的关系，包括来自连续施用有机质或稻田-旱地轮作的处理地块的土壤。尽管火山土壤或非火山土壤的回归斜率不同，但观察到 AN 和 TN 之间存在显着的正相关。由于频繁的稻田-旱地轮作，AN 的下降幅度大于 TN 的下降幅度。另一方面，观察到AN和MWH之间高度正相关，决定系数高于AN和TN。TN和WHC随着稻田土壤有机质积累量的增加而增加。由于 WHC 和 MWH 之间存在正相关关系，AN和MWH之间也观察到正相关。此外，我们使用秋季耕作前收集的表土样本调查了 MWH 的逐年变化，在 24 个地块中连续 3-5 年，针对日本各地的各种土壤类型。为了消除降水的影响并最大限度地减少稻田表土中 MWH 的波动，最好在最后一次 1 mm h 降水的 24-96 小时内收集表土样品^-1或更高，用于测量水分含量。