Effect of green revolution technology during the period 1970-2003 on sawah soil properties in Java, Indonesia: II. Changes in the chemical properties of soils

The effect of green revolution (GR) technology during the period 1970-2003 on changes in a number of chemical properties of sawah soils was studied in Java, Indonesia. The term sawah refers to a leveled and bounded rice fields with an inlet and an outlet for irrigation and drainage. Soil samples taken by Kawaguchi and Kyuma in 1970 and new samples from the same sites or close to the original sites were analyzed and compared. For the 40 sites examined, mean soil pH and exchangeable sodium (Na) decreased from 6.90 ± 0.77 to 5.84 ± 0.90 and from 3.28 ± 2.76 to 1.67 ± 2.06 kmolc ha⁻¹, respectively; while the exchangeable acidity and available phosphorus (P) significantly increased from 9.32 ± 3.09 to 13.23 ± 3.72 kmolc ha⁻¹ and from 136.62 ± 154.72 to 255.75 ± 292.41 kg P₂O₅ ha⁻¹, respectively. There were no significant differences in exchangeable calcium (Ca), magnesium (Mg) and potassium (K) contents and in effective cation exchange capacity (eCEC) during this period. Differences in land management practices may have affected the trends recorded in soil chemical properties in seedfarms where rice has been planted continuously using high doses of chemical fertilizers and in non-seedfarms where farmers use rotation patterns with low fertilizer application. The mean values of soil pH, exchangeable acidity, exchangeable Na and available P in the 0-20 cm soil layer in seedfarms changed by -1.25, 4.11 kmolc ha⁻¹, -1.42 kmolc ha⁻¹ and 194 kg P₂O₅ ha⁻¹, respectively; while in non-seedfarms these soil properties changed by -0.90, 3.26 kmolc ha⁻¹, -1.77 kmolc ha⁻¹ and 57 kg P₂O₅ ha⁻¹, respectively. The mean value of exchangeable K in seedfarms remained at the same level as that recorded in 1970 because of a sufficient supply of KCl as a potassium fertilizer during the study period. In contrast, in non-seedfarms where K fertilizer was applied infrequently, exchangeable K decreased by -0.30 kmolc ha⁻¹. In comparison with results from Bangladesh over a similar period, Bangladesh lost more exchangeable base cations than Java. Available P content decreased by approximately 10% in Bangladesh, whereas in Java it increased almost twofold.