Porous soils are characterized by high infiltration, low moisture retention and poor fertility due to limitation of organic matter and nitrogen (N). However, wherever irrigated and properly managed, these are among the most productive soils in the world. For sustained productivity and prevention of N related pollution problems, fertilizer N management in porous soils needs to be improved by reducing losses of N via different mechanisms. Losses of N through ammonia volatilization are not favoured in porous soils provided fertilizer N is applied before an irrigation or rainfall event. Ammonium N transported to depth along with percolating water cannot move back to soil surface where it is prone to be lost as NH3. Under upland conditions nitrification proceeds rapidly in porous soils. Due to high water percolation rates in porous soils, continuous flooding for rice production usually cannot be maintained and alternate flood and drained conditions are created. Nitrification proceeds rapidly during drained conditions and nitrates thus produced are subsequently reduced to N2 and N2O through denitrification upon reflooding. Indirect N-budget estimates show that up to 50% of the applied N may be lost via nitrification-denitrification in irrigated porous soils under wetland rice. High soil nitrate N levels and sufficient downward movement of rain water to move nitrate N below the rooting depth are often encountered in soils of humid and subhumid zones, to a lesser extent in soils of semiarid zone and quite infrequently, if at all in arid zone soils. The few investigations carried out with irrigated porous soils do not show substantial leaching losses of N beyond potential rooting zone even under wetland rice. However, inefficient management of irrigation water and fertilizer N particularly with shallow rooted crops may lead to pollution of groundwater due to nitrate leaching. At a number of locations, groundwater beneath irrigated porous soils is showing increased nitrate N concentrations. Efficient management of N for any cropping system in irrigated porous soils can be achieved by plugging losses of N via different mechanisms leading to both high crop production and minimal pollution of the environment.

Nitrogen losses and fertilizer N use efficiency in irrigated porous soils

Rice is the most important food crop in the developing countries of Asia, where population densities are very high and overall dietary levels are not adequate. In south and southeast Asia, rainfed and irrigated transplanted rice occupies nearly two–thirds of the rice-growing area and produces more than 80% of the paddy rice. In these areas, prilled urea (PU) conventionally applied by farmers is very inefficiently used by transplanted rice largely because of serious losses (up to 60% of applied N) via NH3 volatilization, denitrification, leaching, and/or runoff. In order to minimize N loss, especially loss due to denitrification, historically the Japanese have used different ways of deep placing fertilizer N. In 1975, IFDC proposed use of supergranules of urea (USG) in place of mudballs containing urea fertilizer to achieve the same agronomic benefits as achieved through the Japanese concept of deeppoint placement of fertilizer N in transplanted rice.

Deep placement of urea supergranules in transplanted rice: Principles and practices

Summary A better understanding of the nutrient economy in relation to productivity is immensely important to develop a sustainable rice-wheat cropping system in the Indo-Gangetic Plain (IGP). Fertilizer (N, P and K) use pattern for the rice-wheat system in the IGP varies greatly at the country, state, village, and farmer field level. In general, fertilizer use is conspicuously more in the western compared to the eastern IGP. Continuous government subsidies on nitrogenous fertilizers have helped create imbalanced N, P, and K fertilizer use by farmers. Removal of P and K by the rice-wheat system far exceeds its additions through fertilizers and recycling. Nitrogen from rice-wheat systems can often be lost via ammonia volatilization, denitrification and leaching. Nitrification acts as a key process in determining fertilizer-use-efficiency by crops as well as N losses from soils. Loss of N via ammonia volatilization can be substantial when urea is top-dressed. Placement of fertilizer N beneath the soil surfac...

Efficient Management of Primary Nutrients in the Rice-Wheat System

Rice (Oryza sativa), one of the most important food grain crops in the world, forms the staple diet of 2.7 billion people. It occupies 150 million hectare and producing 537 million tones with the average productivity of 3.83 tones/ha. Its cultivation is of immense important to food security of Asia, where more than 90% of the global rice is produced and consumed. India is the largest rice growing country, while china is the largest producer of rice. In India more than 40% food grains production comes from rice which provides direct employment to about 70% of working rural people in the country. It International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 6 Number 7 (2017) pp. 2408-2418 Journal homepage: http://www.ijcmas.com

/pdf/effect-of-different-levels-of-nitrogen-on-growth-and-yield-1ryxkqbyyh.pdf

Effect of Different levels of Nitrogen on Growth and Yield of Rice (Oryza sativa L.) Cultivars under Terai-agro Climatic Situation

In a laboratory experiment 5 cm depth of water was allowed to percolate daily down through a 15 cm thick soil (Typic Ustipsamment) layer. It was observed that leaching losses of urea supergranules (USG)-N could be decreased by about 20% by the placement of four 0.25 g granules at four points instead of one 1 g granule at one point. In field microplots, the placement of approximately 30 granules of 0.30 g size instead of 9 granules of 1.00 g size resulted in reduced leaching of USG-N and, in turn, increased rice yield. In a follow-up field study, the advantage of more frequently placed USG was confirmed. As compared with 1 g USG placed in the usual manner in the center of four rice hills, increasing the density of placement in soil produced 15% more rice grain. Further increase in rice yield could be obtained by increasing the number of USG placed in the soil and decreasing the size of the granule from 1.00 g to 0.70 or 0.35 g. With USG of 0.35 and 0.70 g yields were equal or sometimes even slightly higher than with split application of prilled urea on a heavily percolating, low-CEC, light-textured soil.

Effect of granule size and the placement geometry on the efficiency of urea supergranules for wetland rice grown on a permeable soil

Data pertaining to grain yield, yield parameters, and N uptake during different periods of rice growth, in three field experiments, were subjected to the statistical procedure of path coefficient analysis. The observed grain yield response to the applied fertilizer N was predominantly reflected in an increased panicle density and spikelet number. The 1,000‐grain weight was only slightly influenced by N fertilization. Since both panicle density and spikelet number are known to be largely determined within 70 days after transplanting (DAT), N uptake during this ‐period was found to be critical to achieve a maximum grain yield response to applied N. The K uptake during 0–40 DAT correlated positively with panicle density, whereas absorption of N during 40–70 DAT determined both panicle density and spikelet number. Since N uptake during 0–20 DAT exerted a significant positive influence on grain yield through increased panicle density, the basal application of a part of fertilizer at the time of transp...

P. K. Malhotra

Papers

Path coefficient analysis of N nutrition on yield and yield components for rice in a highly percolating soil