Nitrate leaching from pastoral livestock systems is a problem in New Zealand due to its impact on waterways. Up to 90% of the nitrogen coming from farmland originates from the urine patch, an area created when urine (with typically high nitrogen concentration) is deposited on the soil. The concentration of nitrogen is too high for the surrounding pasture plants to take up and ultimately nitrate-nitrogen is lost below the root zone and eventually into waterways.
Ecotain environmental plantain is a natural, plant-based technology which reduces nitrate leaching from the urine patch using four independent mechanisms. This issue of the ‘Ecotain Winter Series’ recaps how two of these functions (delay and restrict) work. Essentially, you can think of them as the soil-centric mechanisms.
The animal centric mechanisms of DILUTE and REDUCE were covered in the last issue of the Winter Series.
To explain how the soil-centric mechanisms function lets recap the nitrogen cycle, shown here in a stylised form. About 50% of the nitrogen ingested by the animal is excreted in urine and deposited on the soil surface in a urine patch. Soil microbes (ammonium oxidising bacteria) convert the mainly ammonium nitrogen into nitrate nitrogen (a process called nitrification). Although the ammonium form is not typically leachable, the nitrate form is very leachable. Nitrate not taken up by the plant is leached below the root zone when water moves through the profile. The higher the concentration in the urine patch the more nitrogen is leached.
In the last issue we recapped how reducing N leaching can be achieved by reducing the amount of N consumed (thus reducing the amount excreted), reducing the proportion of intake excreted in urine (change in N partitioning (REDUCE)), decreasing the N concentration in the urine by increasing urine volume (DILUTE). In this issue we will recap how decreasing the rate at which soil microbes convert the non-leachable urinary N (ammonium) into the much more mobile nitrate form in both the urine patch (DELAY) and in the soil in which Ecotain grows (RESTRICT) reduces the potential for leaching.
Reducing the speed at which urinary N is converted to nitrate N will ultimately reduce N leaching because pasture plants will have a greater period to take up the nitrogen before it is converted to nitrate and potentially lost through leaching.
About 50% of the nitrogen consumed by the grazing animal is excreted in urine mainly as ammonium. Typically, ammonium undergoes rapid nitrification to nitrate (by nitrifying bacteria in the soil) which is leachable. Reducing the speed of nitrification in the soil beneath the urine patch allows pasture plants a longer period to take up the nitrogen. This delay in nitrification may be particularly important in free draining soils where drainage events happen more regularly.
The delay to nitrification is caused by the presence of a biological nitrification inhibitor in the urine of animals grazing Ecotain. Nitrification inhibitors reduce the ability of ammonium oxidising bacteria to convert ammonium to nitrate. Recent incubation experiments have demonstrated that urine from sheep fed Ecotain reduce the build-up of nitrate compared with urine from grass fed animals, such that at 21 days post urine application, nitrate levels from Ecotain treatments were approximately only a third of the ryegrass treatment. Similar work with alike outcomes has been completed on dairy cattle. Current work is focused on identifying the inhibitor and optimising its effectiveness.
Work at Lincoln University with lysimeters provided evidence that reductions in leaching were possible from swards containing the Ecotain cultivar Tonic, with urine from cows grazing ryegrass only. Simply, having Ecotain present in the sward reduced the nitrification rate independent of the urine source (the RESTRICT function).
The soil supporting these swards had a much lower ammonium oxidising bacteria population which is entirely consistent with a reduction in the nitrification rate. Nitrification inhibitors exuding from the roots of Ecotain and their effect on soil bacteria is suspected to be a mechanism involved in the reduction of leaching. Work is currently underway to quantify the amount of Ecotain required to induce this effect.
For more information on Ecotain Environmental Plantain contact your local Farm Source Store.
Article supplied by Glenn Judson – Agricom