Response of rice to nitrogen fertilization in Puerto Rico

Abstract

In Puerto Rico, nitrogen is by far the most important element in rice production. However, responses are oftenly modified by methods of application, water management systems, season of the year, straw management and pest control. Splitting the N applications increased the efficiency as compared to applying all at planting time. Rice yields were increased steadily from 0 to 224 kg of N/ha attaining a maximum yield of about 8 t/ha when all N was applied at once, whereas similar yields were obtained with only 112 kg of N/ha when N was split with no further increase with heavier applications. Residual effect of N was more evident when fertilizer to previous crop was split applying half at planting time and half at panicle initiation. Higher yields and a more efficient use of N is to be expected when rice is planted from January to June. During this season, a maximum yield of 6.7 t/ha of rough rice was obtained with 168 kg of N/ha, whereas when planted from July to November rice barely yielded 5 t/ha and responded to only 112 kg of N/ha. This reduction in yields was probably due to shorter, cloudy days during the rainy season from July to November. Damage by blast which increased also during the season was correlated with N applications. The heavier the N application, the more severe the disease damage. Disking in the straw after cropping, produced somewhat higher yields at comparable N rates than burning or throwing it away. The difference was more evident after the 5th consecutive rice crop.