ABSTRACT

The Green Revolution (GR) made a major contribution to increasing the rice yield in the Philippines from 1.3 t ha⁻¹ in 1966 to 4.0 t ha⁻¹ in 2018, but the changes in paddy soil fertility that occurred during this 50-year period remain unknown. We collected 37 soil samples from the plow layers of paddy fields in Luzon, Leyte, Panay, and Mindanao in the Philippines in 2016 and 2017 (the ‘2010s’) and compared their fertility-related soil properties with published data for soil samples collected from the same or nearby sampling sites in 1969 (the ‘1960s’). Paddy soils in the Philippines had relatively high exchangeable calcium (Ca) and magnesium (Mg) content, cation exchange capacity (CEC), available silicon (Si) content, and total carbon (C) and nitrogen (N) content, reflecting their indigenous pedological background. We found that the 2010s soils had a lower available N content, particularly in wetter regions, despite the high input of N fertilizers, whereas the available phosphorus (P) showed a six-fold increase from the 1960s to the 2010s. The total potassium (K) content had significantly decreased during this period, possibly due to the mining effect of intensive farming with K-deficient fertilization. The 2010s soils contained a greater silt content and higher proportion of smectite in the clay fraction, which may have been transported from upstream via irrigation water. The increase in smectite corresponded with a significant increase in the cation exchange capacity, despite the organic C and clay contents tending to decrease, and these increases in smectite and soil pH may have contributed to the increase in the available fraction of Si that had not been applied as fertilizers. These findings demonstrate that paddy soil fertility in the Philippines changed in many ways over this 50-year period, largely owing to the direct impact of GR implementation in paddy fields but also potentially due to offsite effects from upland fields. The environmental impact of the nutrient loss and soil organic matter degradation behind the fertility improvement should be assessed holistically for the sustainable development of rice paddy ecosystems. (337 words)

摘要

绿色革命 (GR) 为将菲律宾的水稻产量从1966 年的1.3 吨公顷^{-1 提高}到 4.0 吨公顷^-1做出了重大贡献2018 年，但在这 50 年期间发生的水稻土壤肥力变化仍然未知。我们于 2016 年和 2017 年（“2010 年代”）从菲律宾吕宋岛、莱特岛、班乃岛和棉兰老岛的稻田犁层收集了 37 个土壤样本，并将其与肥力相关的土壤特性与从1969 年（“1960 年代”）相同或附近的采样点。菲律宾稻田的可交换钙 (Ca) 和镁 (Mg) 含量、阳离子交换容量 (CEC)、有效硅 (Si) 含量以及总碳 (C) 和总氮 (N) 含量相对较高，反映了其本土土壤学背景。我们发现 2010 年代土壤的有效氮含量较低，尤其是在较潮湿的地区，尽管氮肥的投入很高，而有效磷 (P) 从 1960 年代到 2010 年代增加了 6 倍。在此期间，总钾 (K) 含量显着下降，可能是由于缺乏钾肥的集约化农业的采矿效应。2010 年代的土壤含有更多的淤泥，粘土部分中蒙脱石的比例更高，这可能是通过灌溉水从上游运来的。尽管有机碳和粘土含量趋于降低，但蒙脱石的增加与阳离子交换能力的显着增加相对应，并且蒙脱石和土壤 pH 值的这些增加可能有助于增加未经过用作肥料。这些发现表明，菲律宾水稻土壤肥力在这 50 年期间发生了许多变化，主要是由于水稻田中遗传资源实施的直接影响，但也可能是由于旱地的异地影响。为了稻田生态系统的可持续发展，应全面评估肥力改善背后的养分流失和土壤有机质退化对环境的影响。(337 字)