Reassessing the critical reading of leaf color chart in an organic-based nutrient management in paddy rice

The leaf color chart (LCC) was developed for effective nitrogen management for rice. The existing LCC technique was optimized under irrigated rice ecosystem as part of a judicious use of chemical fertilizers, and without the use of organic fertilizer as part of this nutrient management. With the increasing advocacy in pure organic and in organic-based rice farming, there is now a question whether the efficiency of LCC in paddy rice applied with chemical fertilizers is the same in paddy rice app0lied with organic fertilizers. This study was established at PhilRice Central Experimental Station with Maligaya clay soil series and Type 3 climate. PSB Rc82 a popular high yielding variety was the test variety. Two LCC readings were re-assessed and different topdressing materials were compared: green manure (Tithonia diversofolia), urea, inorganic foliar, and organic foliar. Basal fertilizers are rice straw compost (RSC) and RSC with chicken manure (RSCCM). The treatments were laid-out in Splitplot design in 4 replications. Results had elucidated previous experiment on the apparent incompatibility of the critical reading of LCC 3 in a pure organic based nutrient management (OBNM). When organic fertilizer (rice straw compost) was basally incorporated, the LCC 4 showed to be a better critical reading for top dressing of fertilizer than LCC 3. Apparently, the presence of organic matter requires higher N level as the rice plants grow. Also, the yield response of PSB Rc82 was highest when urea was applied at the critical LCC reading of 4. In this study, foliar fertilizer, be it in organic or inorganic source apparently was not as good as the granular topdress fertilizers. Basically, this is due to the higher N content from the latter than the former. Rice straw compost with or without the addition of chicken manure can be used as basal organic fertilizer.