| Summary: | ABSTRACT
Research of P K fertilization and frequency of K fertilizer application on cassava in Vertisol upland was conducted in Wonosari subdistrict, Gunungkidul regency at planting season 2001. The objective of the research was to look for the technology for increasing P and K fertilization efficiency on cassava in Vertisol upland. The research consisted of two trials. The factorial randomize block design was used in these trials. The treatments of first trial were combination of three cassava varieties (Malang-4, Malang-1 and local variety), three rate of P fertilizer (0, 75 and 150 kg SP36/ha) and two rate of K fertilizer (0 and 100 kg KC1/ha). All treatments were fertilized by 200 kg Urea/ha. The treatments for second trial were combination of two kinds of N fertilizer ( 200 kg Urea/ha and 150 kg Urea + 100 kg ZA/ha), two rate of P fertilizer ( 0 and 100 kg SP36/ha) and five times of K fertilizer application.
The results of the research showed that two introduction cassava varieties (Malang-1 and Malang-4) could not be used to substitute the local variety in that marginal upland. The application of 100 kg SP36/ha increased the P nutrient absorption by plant and tuber yield than zero P fertilizer. The application of 100 kg KC1/ha increased K nutrient absorption if it's application was combined with P fertilizer (75 or 100 kg SP36/ha) even though did not increase tuber yield. Five times of K fertilizer application in fact reduced K and P absorption by plant as well as tuber yield. The highest tuber yield was only 20 t/ha and it was far lower than its potential yield and it needs a further research.
Key words: Cassava, PK fertilization, Vertisol upland.
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