Soil N process inhibitors alter nitrogen leaching dynamics in a pumice soil

Abstract

A field lysimeter experiment, using a free-draining pumice soil, was carried out to investigate the effect of different soil nitrogen (N) process inhibitors on the fate of 15N-labelled cow urine. The treatments were a urease inhibitor (Agrotain; N-(n-butyl) thiophosphoric triamide), 2 nitrification inhibitors (dicyandiamide, DCD; 4-methylpyrazole, 4MP), a combination (DCD+Agrotain), a urine control, and a nil urine. The inhibitors were mixed with cow urine, which was then applied in a single application (equivalent to 775 kg N/ha) to lysimeters in autumn and monitored over the following 196 days. DCD and 4MP similarly reduced nitrate leaching by 59%, from 114 to 47 kg N/ha compared with the urine control. Of the DCD applied, 58% of it (8.7 kg/ha) was recovered in leachate, and represented an N loss of 5.8 kg/ha. The presence of Agrotain reduced ammonia (NH3-N) emissions by 64% (equivalent to 70 kg N/ha) over the short term (first 20 days), but led to large leaching losses of urea-N (25 kg N/ha) over the medium term (76 days). The Agrotain-DCD combination resulted in even larger losses of urea-N (45 kg N/ha). The major N component measured in leachate (below 450 mm) was ammonium-N, which constituted about 60% of the average total N (205 kg N/ha) leached. Ammonium-N leaching was rapid and almost entirely driven by macropore flow processes. Further research is required in deeper soil profiles, and in relation to climatic risk of high early rainfall on fresh urine patches, to determine the importance of macropore processes on N loss under typical on-farm soil conditions.

The Challenge of the Urine Patch for Managing Nitrogen in Grazed Pasture Systems

“…Cameron (2002c, 2004) measured significantly greater N uptake (and dry matter yield) of pasture from urine-treated lysimeters when the nitrification inhibitor DCD was applied. Menneer et al (2008a) recovered 20% of applied 15 N from an autumn urine application (775 kg N ha À1 ) but this increased to 27% where urease and nitrification inhibitors were added to the urine to decrease both NH 3 volatilization and NO À 3 leaching. Shepherd et al (2014) found a positive correlation between N saved from leaching by DCD application and increased pasture N uptake in a lysimeter study (i.e., equivalent to urine patch level).…”

“…Menneer et al (2008a) measured losses of 109-kg NH 4 -N from a urine application (775 kg N ha À1 ) due to macropore flow and high rainfall/drainage, albeit the lysimeters were only 450-mm deep. Shepherd et al (2010) measured >30 kg urea-N ha À1 leached below 700-mm deep (1000 kg N ha À1 applied) in the first drainage events after application, again attributing this to macropore flow.…”

The effectiveness of a granular formulation of dicyandiamide (DCD) in limiting nitrate leaching from a grazed dairy pasture

“…In practice, most nitrate leaches from urine patches deposited over a series of grazings during autumn and winter. The benefit of DCD use will therefore depend on factors that include the timing of DCD applications relative to grazing, and the longevity of DCD in soil, which in turn is known to be influenced by temperature and surplus rainfall (Slangen & Kerkhoff 1984;Menneer et al 2008b). …”

Application of carbon additives to reduce nitrogen leaching from cattle urine patches on pasture

“…Williams and Haynes 2000;Wachendorf et al 2005;Menneer et al 2008). The 67% 15 N recovery in soil plus pasture across treatments indicates that about one third of the applied urine-N was lost from the system, either by leaching or in gaseous forms.…”

“…Lysimeter collection and installation Forty intact soil monolith lysimeters (300 mm diameter, 500 mm depth) encased in polyvinyl chloride (PVC) cylinders were collected from a free-draining Horotiu silt loam soil (typic orthic allophanic soil (Singleton 1991)) under permanent pasture, using the technique described by Menneer et al (2008) and Cameron et al (1992). Chemical properties of the 0Á7.5 cm soil layer were thus: pH (water) 5.9; organic C 6.5%; total N 0.56%; cation exchange capacity 22 cmol c kg (1 .…”