Solving problems concerning the effects of agriculture on the land.
Research at Lincoln University by Prof. Keith Cameron and associates.
Concerns over water quality (e.g. Lake Taupo is polluted from the land)
- Nitrates from dairy pasture.
Intro:
How would you get underground to measure the amount of nitrates that get washed
through the soil and enter waterways?
Responses: dig the ground, auger, drill holes, measure what is in soil, analyse water.
Underground lysimeter lab facility
The lysimeter involves collecting large drums of undisturbed soil (i.e. earthworms, root
structures etc. all included and intact) and installing back into the ground. The drum begins
as a large empty metal casing, and after collection and installation, the soil inside the
lysimeter is level with the ground, therefore this area will receive the same amount of
sunshine and rainfall as its surroundings. At the base of each lysimeter is a rubber tube
leading to a collection bag to capture drainage water.
Urine is applied to the tops of the lysimeters and the liquid that percolates through is
collected below in the bags. This simulates the leaching that happens on a dairy farm. Gas
emitted from the applied urine can be measured from these lysimeters also.
The air is conditioned underground to match the outside soil temperature.
The nitrate leaching comes mostly from the highly concentrated urine patches and not
directly from the fertiliser. Most of the nitrogen in the feed consumed by the animals is
excreted in the urine (creates “nitrogen hotspots”).
How can we solve this?
1. Feed cereals rather than pasture to the cows as these contain less nitrogen
(Un-economic)
2. Attach spray plates to rear of cows to distribute urine over bigger area
(Difficult to do and many would perceive this as being inhumane)
3. Collect all drainage water from grazed land to prevent contamination of underground
water
(Impossible!!)
- Therefore other more feasible and less costly technologies are required to solve this
problem.
The Nitrogen Cycle
The nitrogen is part of a cycle in the soil. The NH4+ (ammonium cation) sticks to the
negatively charged soil and provides a store of ammonium for the plants to use. Once it is
converted into nitrate (NO3-) it is repelled by the soil and is leached out (washed out).
Various groups of bacteria in the soil convert ammonium into nitrate (process known as
nitrification) and the rate of activity of these bacteria can be slowed down by inhibitors,
especially in the winter when the plants are not growing and do not need so much nitrogen.
Furthermore, drainage mainly occurs during the winter, and is responsible for nitrate
leaching (water acts as a transportation vessel in soil).
- Nitrate content can be measured in the urine and in the drainage water collected below
the lysimeter.
Trials have been ongoing for approx. 10 years and the reduction in nitrates after using the
inhibitor Eco-n is 50-70%. The inhibitor must be applied in both autumn and spring as the
active ingredient is biodegradable by soil microbes within 3 months. This inhibitor is non
toxic, in fact it is 3 x safer than salt on our food.
In NZ greenhouse emissions come mainly from cows. There are only 4 million people and
half the greenhouse gases come from agriculture and the other half from carbon dioxide.
Greenhouse gas emissions are causing climate change. In other countries heavy industry,
power and steel production release most CO2 which is their main greenhouse gas.
In NZ 1/3 of gas emissions produced through agriculture is nitrous oxide (N20) and 2/3
methane (CH4 - belched from cows).
The N20 is released from the soil and is captured using a chamber over the lysimeter. The gas
is collected and the content is analysed.
N2O is a by-product of nitrification, and can also be derived from nitrate, therefore by
slowing down nitrification, N2O emission is also reduced (studies have shown a reduction in
N2O emission of approx. 70%+ when Eco-n is used)
Currently there are no financial incentives to dairy farmers to use this inhibitor to reduce
nitrate run off. Overseas taxes are paying for emissions and so reducing emissions will result
in reduced taxes. Government talks about carbon credits for farmers are still in progress
here.
Because Eco-n conserves soil nitrogen and prevents it from being leached or emitted, the
pasture also grows better (approx. 20% better) because more nitrogen is available in
ammonium form for plants to use. Less nitrogen fertiliser is then needed for pasture growth
because Eco-n prevents nitrogen from urine and fertiliser being wasted (leached or emitted).
In summary - More nitrogen will remain in soil/ less nitrogen leached in drainage water/
less emitted as a gas/ more pasture growth for farmers.
Economics:
Ravensdown fertiliser is producing Eco-n. It is 10-12cents per kg of extra dry matter grown. A
valuable proposition for farmers as grass is grown more cheaply. Cost comparisons can be
made: Grain is more expensive than silage so more grass is grown for less cost to farmers.
Farmers are starting to see the benefits - 25% of dairy farmers are using this technology in
Canterbury and less than 5% nationwide. Time is needed to properly educate farmers about
this technology as it is not simply a fertiliser like farmers are currently using.