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TROPICAL SOIL MANAGEMENT

Stover and Potassium Management in an Upland Rice–Soybean Rotation on an Indonesian Ultisol

^a Jasa Katom, Jalan Kehakiman No. 283, Bukittinggi, West Sumatra, Indonesia 26136
^b Dep. Agronomy and Soil Sci., Univ. of Hawaii, Honolulu, HI 96822 USA

katom{at}bukittinggi.wasantara.net.id

Fertilizer and stover management greatly determine the extent of K deficiency on weathered, low-K soils in the humid tropics. This study quantified the effects of K fertilization and stover management on soil properties and crop yields on a Typic Kanhapludult in Indonesia. Cowpea [Vigna unguiculata (L.) Walp. subsp. unguiculata]–cowpea–rice (Oryza sativa L.)–soybean [Glycine max (L.) Merr.]–rice–soybean were grown during a 2-yr period. Fertilizer KCl was applied as 70 and 250 kg K ha^-1 to the first crop only, and as a total of 250 and 600 kg K ha^-1 applied to several crops. The effect of stover removal or return was examined for each K rate. Critical soil K levels were 0.14 cmol_c kg^-1 for the final rice crop and 0.14 and 0.16 cmol_c kg^-1 for the two soybean crops. By returning stover, a single application of 70 kg K ha^-1 to the first crop was adequate to maintain soil K above the critical level for all six crops. When stover was removed, a total of 250 kg K ha^-1 applied during several crops maintained soil K above critical levels. A one-time 250 kg K ha^-1 application to the first crop, however, resulted in yield declines by the fifth crop. A maintenance rate of about 45 kg K ha^-1 per crop was required when stover was removed. Stover removal also hastened soil Mg depletion, and thus a maintenance rate of about 6 kg Mg ha^-1 crop^-1 is recommended.

Abbreviations: DAP, days after planting • ECEC, effective cation exchange capacity