Fertilizer management of upland rice (Oryza sativa L.) grown on lahar deposit

Nitrogen level had a positive linear relationship with plant height at maturity, number of non-productive tillers/pot, number of panicles/pot, straw yield/pot, and grain-to-straw ratio within the range 90-180 kg N/ha. One thousand grain weight increased with the addition of nitrogen up to 128 kg/ha, but not beyond. Nitrogen level did not affect days to flowering, days to maturity, and percent ripened grains. Method and time of nitrogen application influenced plant height at maturity, number of non-productive tillers/pot, number of panicles/pot, percent ripened grains, 1000-grain weight, straw yield/pot, and grain-to-straw ratio. In all these variables, 6 topdressings (6TD) performed best. Basal and 2 top dressings (B + 2 TD) delayed flowering compared to 6TD and 2 TD and 6 foliar sprays (2 TD + 6 S). Days to maturity was not affected by method and time of nitrogen application. The linear trend of nitrogen level interacted with method and time of nitrogen application in number of spikelets/panicle, number of ripened grains/panicle, and grain yield/pot. In all these variables, the response to nitrogen level was in the order of 6 TD 2 TD + 6 S B + 2 TD. Chicken manure (CM0 was added inorganic fertilizer (AIF) did not influence days to flowering and days to maturity, but variety did. The modern variety UPLRi5 flowered and matured earlier than the traditional variety Palawan. CM had a positive linear relationship with number of non-productive tillers/pot, number of spikelets/pot, 1000-grain weight, grain yield/pot, and grain-to-straw ratio within the range 0-60 tons CM/ha. Application of inorganic fertilizer as supplemented to CM at the rate of 60-60-60 (60 AIF) and 90-60-60 (90 AIF) increased number of panicles/pot, number of spikelets/panicle, number of ripened grains/panicle, percent ripened grains, grain yield/pot, and straw yield/pot over non-application of inorganic fertilizer (no AIF). But at least 90 AIF is required to increase 1000-grain weight and grain-to-straw ratio above that from no AIF. The plant height response to level of CM was influenced by AIF. With AIF the plant height response to CM level was linear, without AIF, the response was quadratic. UPLRi5 had higher number of non-productive tillers/pot, number of panicles/pot, 1000 grain weight, and grain-to-straw ratio, but lower number of spikelets/panicle, number of ripened grains/panicle and straw yield/pot than Palawan. Also it flowered and matured earlier, and was shorter than Palawan. The linear trend of CM interacted with variety on number of panicles/pot and straw yield/pot. UPLRi5 had a higher response to CM level than Palawan in terms of number of panicles/pot, but a lower response in terms of straw yield/pot. The percent-ripened-grain responses of UPLRi5 and Palawan to CM, levels were both quadratic, but both regression coefficients were higher in Palawan than in UPLRi5. On number of ripened grains/panicle, the response of UPLRi5 to CM level was linear, but that of Palawan was quadratic. In terms of grain yield 180-60-60 alone, applied 6 times by topdressing was equivalent to 40 tons CM plus at least 60-60-60 per hectare (40 cm + 60 AIF). The organic matter [OM] content and cation exchange capacity [CEC] of the lahar deposit after the experiment increased linearly with CM level up to 60 tons CM/ha. Although there was no linear trend, the water holding capacity of the lahar deposit after the experiment was also increased by CM and was highest at 60 tons CM/ha. However, in spite of the increase in values, the OM content, CEC and water-holding capacity of the lahar deposit after the experiment were still very low