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7.4.8. Varieties and fertilizing Application of excess nitrogen to traditional tall varieties will increase their height and tendency to lodge, resulting in low grain yield. Modern semidwarf varieties are well responsive to nitrogen application. The grain yield due to larger amounts of nitrogen application is higher in modern varieties than in traditional tall varieties.

7.4.7. Soil fertility and fertilizing Larger amounts of fertilizer should be applied in poor soil compared to fertilizers applied in fertile soil. Much nitrogen fertilizer in fertile soil causes excessive vegetative growth, resulting in poor light distribution and lodging. Excess nitrogen at late growth stage increases spikelet sterility, resulting in lower grain yield.

7.4.6. Seasons and fertilizing Larger amounts of fertilizers can be applied during dry season compared to fertilizers applied during wet season. Rice plants are tall during wet season. They shade each other due to their leafiness. They can not fully make use of nitrogen fertilizers applied during wet season.

7.4.5. Application methods To minimize the loss and to increase the efficiency of fertilizer use, the fertilizers should be properly mixed into soil. The basal fertilizers have to be applied just before final harrowing to allow thorough incorporation of the fertilizers with soil. However, fertilizers except the basal are usually topdressed.

7.4.4. Appling amounts and rates According to many data and research results, 20-200 kg nitrogen per hectare is applied to rice crop. When the nitrogen requirement of the field is low, equal splits for basal application and topdressing may be done around transplanting stage and 5-7 days before panicle initiation. The appling amounts and rates may greatly differ depending on cultural conditions...

7.4.3. Application times Two particular times for transplanted rice are responsive to nitrogen application. The first is done just before final harrowing to allow thorough incorporation of urea with the soil. The second is done 5-7 days before panicle initiation to increase the number of spikelets per panicle. Split application increases fertilizer effectiveness.

7.4.2. Fertilizer effectiveness Nitrogen is used in the greatest quantity among all fertilizers. But it is subject to great loss through holding by soil particles, volatilization, and seepage. Generally, the recovery of nitrogen fertilizers applied to the rice crop ranges from 30% to 50%. To minimize the loss and to maximize the use of the available nitrogen are important. 7.4...

7.4.1. Functions Nitrogen is essential to plant growth such as increased height, produced tillers, increased size of grain, increased number of spikelets per panicle, etc. Nitrogen gives dark green color to plant parts as a component of chlorophyll. Nitrogen increases protein content in the rice grains. Nitrogen deficiency is first visible in old leaves due to its mobility inside the plant.

7.3.2. Inorganic fertilizers Inorganic fertilizers indicate commercially manufactured mineral nutrients. There are some sorts of combinations of nitrogen, phosphorus, potassium, and sulfur fertilizers. The numbers on the bag indicate the percentage by weight of mineral nutrients in the fertilizer. 20-10-10 on the bag means 20% nitrogen, 10% phosphorus, and 10% potassium.

7.3.1. Organic fertilizers Continuous application of inorganic fertilizers can cause deterioration in soil productivity. Uses of organic fertilizers improve the soil structure and can increase the crop productivity in the soil. Organic fertilizers come from farm wastes and green manure such as crop residues, animal and human manure, cowpea, plants leaves, etc.