Lime and fertilizer are required to overcome acidity and soil fertility constraints to crop production in the highly weathered soils of Sitiung, Indonesia. The potential leaching of soil amendments is enhanced by the high annual rainfall of 2750 mm and the low effective cation exchange capacity (ECEC) of these soils. The purpose of this study was to understand the relationship of soil water hydrology to the fate of applied soil amendments. Internal soil water drainage (fieldmeasured) and soil moisture release curves (field‐ and laboratorymeasured) were determined to characterize the soil hydraulic properties of a clayey, kaolinitic, isohyperthermic Typic Kanhapludult. The results indicated that 6 h after the application of 72.5 mm of water during a 100‐min period, water equivalent to nearly 94% of the applied water drained to depths below 112.5 cm. Macropore volume accounted for 26 to 40% of the total porosity of the top 22.5 cm of soil and 5 to 7% in the 22.5‐ to 112.5‐cm depth. Cation movement was measured during a 2‐yr period in a field experiment that examined the effects of various rates and timing of K fertilization (and blanket applications of Ca and Mg) and stover removal on soil K, Ca, and Mg pools. Results show that amounts equivalent to 1% of the K, 5% of the Ca, and 24% of the Mg that were applied as fertilizer nutrients accumulated in the 30‐ to 90‐cm depth. An average of 33% of the K, 26% of the Ca, and 8% of the Mg applied as fertilizers were not accounted for in the soil or by crop biomass and probably leached below the 90‐cm depth. We conclude that is difficult to chemically ameliorate the subsoil below the 30‐cm depth and hypothesize that macropore flow through the soil and a continually wet subsoil are the major factors limiting subsoil cation accumulation.
Potassium and stover management are critical to the uplands of Sitiung, Indonesia, where the predominant Fertilizer and stover management greatly determine the extent of cropping system is upland rice followed by soybean or K deficiency on weathered, low-K soils in the humid tropics. This study quantified the effects of K fertilization and stover management peanuts (Colfer, 1991). Rice stover (straw) in this system on soil properties and crop yields on a Typic Kanhapludult in Indone-is usually burned in piles after threshing. Even if farmers sia. Cowpea [Vigna unguiculata (L.) Walp. subsp. unguiculata]rotate the location of the rice burn piles each season, cowpea-rice (Oryza sativa L.)-soybean [Glycine max (L.) Merr.]incorporation of burnt stover generally results in an rice-soybean were grown during a 2-yr period. Fertilizer KCl was uneven distribution of nutrients, which can hasten nutriapplied as 70 and 250 kg K ha Ϫ1 to the first crop only, and as a total ent depletion. The large concentration of cations in one of 250 and 600 kg K ha Ϫ1 applied to several crops. The effect of stover area may exceed the soil effective cation exchange caremoval or return was examined for each K rate. Critical soil K levels pacity (ECEC) and render the nutrient cations susceptiwere 0.14 cmol c kg Ϫ1 for the final rice crop and 0.14 and 0.16 cmol c kg Ϫ1 ble to leaching losses (Ritchey, 1979). The objectives of for the two soybean crops. By returning stover, a single application of this experiment were to (i) quantify the effects of vary-70 kg K ha Ϫ1 to the first crop was adequate to maintain soil K above the critical level for all six crops. When stover was removed, a total ing rates and timing of K applied as fertilizer KCl or of 250 kg K ha Ϫ1 applied during several crops maintained soil K above cattle manure and crop stover return or removal on soil critical levels. A one-time 250 kg K ha Ϫ1 application to the first crop, base cation status; and (ii) relate the effect on base however, resulted in yield declines by the fifth crop. A maintenance cation status to crop yields for a 2-yr period during rate of about 45 kg K ha Ϫ1 per crop was required when stover was which six crops were grown. removed. Stover removal also hastened soil Mg depletion, and thus a maintenance rate of about 6 kg Mg ha Ϫ1 crop Ϫ1 is recommended. MATERIALS AND METHODS Site Characteristics H ighly weathered, leached Ultisols and Oxisols are Field experiments were conducted at a site near the village often used for the expansion of agricultural proof Sitiung 1Á , West Sumatra, Indonesia (102Њ E, 1Њ S), from 1989 to 1991. The rainforest originally covering the site was duction in Indonesia (Donner, 1987). Although soil cut and cleared by bulldozer in 1976. After three seasons of acidity and low soil P are the major fertility constraints rice, the field was fallowed and became covered with alangin these soils, K usually becomes limiting to crop growth alang grass [Imperata cylindrica (L.) P. Beauv.]. In 1989, the under continuous cultivation (von Uexkü ll, ...
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