Regional councils are placing restrictions on the amount of nitrate leached from farmland. The aim of these restrictions is to improve the quality of surface water which includes lakes and rivers. Nitrate is not the only aspect of water quality which needs attention, but it is probably the most difficult because riparian planting and fencing off waterways which reduces phosphate, sediment and E.coli pollution is ineffective against nitrate leaching.
Its been well documented that the predominant source of nitrate leaching out of farmland is from the urine patch – an area created when urine with 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 is a natural technology which reduces nitrate leaching from the urine patch using four independent mechanisms. This issue of “the winter series” recaps how two of these functions (dilute and reduce) work function. Essentially, you can think of them as the animal-centric mechanisms.
To explain how the animal centric mechanisms function lets recap the nitrogen cycle, shown here is 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 convert the mainly ammonium nitrogen into nitrate nitrogen which is 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.
Reducing N leaching can be achieved by reducing the amount of nitrogen consumed (thus reducing the amount excreted), reducing the proportion of intake excreted in urine (change N partitioning away from urine REDUCE), decreasing the n concentration in the urine by increasing urine volume DILUTE and by decreasing the rate at which soil microbes convert the non-leachable urinary N into the much more mobile nitrate.
Reducing the amount of nitrogen and/or concentration of nitrogen in the urine will ultimately reduce N leaching because the plants will leave less residual nitrogen in the urine patch.
About 50% of the nitrogen consumed by the grazing animal is excreted in urine. Reducing the amount of nitrogen consumed (using low N diets such as fodder beet for example) will ultimately reduce N loading in the urine patch but in many situations reducing N intake is not easily achieved especially in pasture-based systems in autumn and spring. It stands to reason that if we cannot reduce N intake then reducing the proportion of diet N excreted in urine could help reduce the loading of nitrogen in the urine patch.
Indoor studies where intake and urine can be accurately measured provide some evidence that animals consuming Ecotain excrete less of their dietary nitrogen into urine. There are probably two common questions around this function. Firstly, if nitrogen is not being excreted into urine, where does it go? There is evidence that more is present in dung, which does not present the same leaching risk as urine, and more of it is found in milk, not necessarily as milk urea but possible as more milk protein. The second question often asked is how does this change in partitioning happen? We don’t fully understand the mechanism of change sin N partitioning, but Massey University researchers have demonstrated Ecotain can affect the microbes of the rumen reducing rumen ammonia and thus reducing the amount of N cleared in urine. Regardless of what causes this, reducing the proportion of dietary N being excreted in urine aids in the reduction of nitrate leaching through its effect on urine patch load.
“Dilution is the solution to pollution”.
Reducing the concentration of nitrogen in the urine patch indeed has a large effect on amount of nitrate leached. That’s because the pasture plants within the urine patch are capable of taking up a greater proportion of the total N loading and therefore the soil residual N is lower.
Dilution of the nitrogen in urine is achieved through two processes. Firstly, urine volumes of animals grazing Ecotain are higher than perennial ryegrass for example because animal grazing Ecotain eat more water. The table below (or to the left or right) shows the amount of water eaten in feeds of different dry matter percentages. The differences a few percentage points in dry matter makes to the total amount of water consumed is considerable. Urine volume ultimately the difference between water consumed and that lost through other routes (eg. faeces, skin and respiration) so the greater the intake of water the higher the urine volume (all else being equal).
However, at the same water intake, a higher urine volume can be achieved if diuretic substances are present. Diuretic substance are those that promote increases in urine volume. There are a number of different ways they work (a description of which is beyond the scope of this publication) but many reduce the reabsorption of water at the kidneys through osmotic pathways. There is clear evidence that Ecotain either contain diuretic substances or produces them as a production of digestion increasing urine volume. Our recent work with sheep suggests an extra 30% urine volume can be achieved from a similar water intake.
A majority of work has been done on full diets of Ecotain but there an emerging thought that Ecotain needs to make a minimum of 30% of an animal’s diet in order that significant reductions in urinary N concentration are achieved.
Keep a look out for the next issue where we will recap the other two mechanisms ‘delay’ and ‘restrict’, the soil-centric mechanisms.
For more information on Ecotain Environmental Plantain contact your local Farm Source Store.
Article supplied by Glenn Judson – Agricom