Nitrogen losses and fertilizer N use efficiency in irrigated porous soils

Abstract

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 N20 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.

Antecedent flow conditions and nitrate concentrations in the Mississippi River basin

“…These may include increased plant stress resulting in low nitrate uptake and low crop yields (Groves and Bailey, 1997), decreased microbial processes resulting in more limited denitrification (Ashby et al, 1998;de Klein and van Logtestijn, 1996) and decreased runoff and leaching (Emmerich and Heitschmidt, 2002;Stites and Kraft, 2001). The timing of fertilizer application before or after a rainfall or irrigation event also influences the amount of available nitrate in the soil (Aulakh and Bijay-Singh, 1997). Additionally, droughts and periods of low flow typically coincide with lowered water tables, decreased hydrologic storage, and decreased hydrologic connectivity, all of which inhibit nitrate transport to streams (Bernal and Sabater, 2012;Detty and McGuire, 2010;Macrae et al, 2010).…”

“…Approximately 25 percent of cropland in the Missouri River basin is irrigated, making it the most irrigated basin in this study (Table 1). During droughts, irrigation may remove nitrate from the soil horizon by leaching, denitrification, or uptake by crops (Aulakh and Bijay-Singh, 1997;Dinnes et al, 2002). Leached nitrate typically moves downward below the active root zone, leading to elevated nitrate concentrations in groundwater (Burkart and Stoner, 2008;Stites and Kraft, 2001).…”

Nitrogen Transformations in Submerged Soils

“…One such example is northwestern India where relatively high solar radiation, together with irrigation and nutrient inputs, enables the porous soils to be very productive (Aulakh and Bij ay-Singh, 1997). Irrigation and rain can transport urea N and ammoniacal N following fertilization into soil where it is more prone to nitrifi cation-denitrifi cation than NH 3 volatilization.…”

Identification of arbuscular mycorrhiza-inducible Nitrate Transporter 1/Peptide Transporter Family (NPF) genes in rice

“…Indeed, experiments with partial NH 4 + and NO 3 − supply and model calculations revealed that NO 3 − absorption and assimilation by wetland plants like rice is particularly efficient (Kronzucker et al 1999;Kronzucker et al 2000;Kirk and Kronzucker 2005;Duan et al 2007). Nevertheless, the agronomic practice of alternating flooding and draining of paddy rice fields may cause loss of up to 50% of applied N via nitrification-denitrification processes (Aulakh and BijaySingh 1997). Most land plant species (70 to 90%), including wetland and semi-aquatic plants, gain access to limited mineral nutrient resources when forming symbiotic associations with arbuscular mycorrhizal fungi (AMF) (Smith and Read 2008).…”