Nevada

GYPSUM SOLVES SODIUM ACCUMULATION

DAIRY WASTEWATER CAN BE A

useful resource for pasture and crops, however high sodium levels in the wastewater may accumulate in soil and cause drainage issues.

Excess sodium leads to low soil water availability and poor soil structure. Soil structure effects may reduce the ability of the soil to receive dairy effluent before surface ponding or runoff occurs.

Gypsum is ideal to address any building of sodium in soils receiving dairy effluent, extending the number of years that affected land remains useful for receiving wastewater. Gypsum can also enhance soil structure, water infiltration and drainage in the face of high sodium levels. A gypsum programme should ideally start before critical sodium levels are reached.

Sodium in wastewater largely comes from the use of caustic soda and sodium hypochlorite in cleaning and sterilising processes. Sodium is relatively easily leached and gypsum accelerates that leaching to reduce the chance of sodium accumulation.

Gypsum is hydrated calcium sulphate. Calcium from gypsum replaces sodium in the soil. The sulphate allows the sodium to be effectively leached out of the soil. The soil then has more ability to flocculate and form stable aggregates to improve drainage and soil quality.

The combination of calcium and sulphate effectively addresses sodium.

Calcium release from the partially soluble gypsum is faster than from lime (calcium carbonate). Lime is also unsuitable in many cases as it acts to increase soil pH, pushing out acid hydrogen rather than sodium from the cation exchange.

Gypsum is typically and most easily applied as a broadcast application to the soil surface. This is also the recommended method if soil crusting is to be addressed. Incorporation of gypsum into the soil is not generally required as the gypsum can work through the profile of most soils.

Gypsum can be applied annually or every two or three years, at higher rates.

Many soils will have quite high thresholds for sodium before soil structure is affected. This depends on the balance of the monovalent cations (sodium and potassium) with calcium and magnesium, and the electrical conductivity of the soil. It also appears that soil resilience to sodium is increased by the organic content (lactose etc) in dairy effluent (Cameron et al., 2003).

Application of gypsum will be most effective if commenced before soil structure is impacted by the sodium and potassium.

Sometimes subsoil structural issues can reduce drainage and impact on the ability of a site to receive wastewater without ponding or surface runoff.

Gypsum may be helpful if the issue is related to sodium and dispersive clay content (clay that loses structure in contact with water), or if there is a problem with high aluminium availability in an acid subsoil.

Gypsum can also reduce surface runoff of phosphorus and other nutrients by improving water infiltration (through soil structural and chemical changes), by binding organic matter and soil particles together better, and by increasing the ability of soil to drain and thus cope with larger water inputs.

Gypsum also increases the binding of phosphate to soil minerals including calcium and reduces the susceptibility of all forms of phosphorus to drainage losses.

More? Visit www.gypsum.co.nz

Applying Gypsum aids with drainage.

NEW COW SHED = NEW OPPORTUNITIES

WAIMACHER FARMS’ OWNERS don’t let opportunities pass them by.

Aaron Waimacher has been running two neighbouring properties and when the opportunity arose to buy an adjacent block, the company grabbed it. From there it was full steam ahead in amalgamating the farms and building a new cow shed which also meant a new effluent management system.

“Amalgamating the farms provided us the opportunity to make everything more efficient. Investing in a new cow shed and effluent system just made sense,” Aaron says.

Once plans for the cow shed were underway it was time to focus on how to manage the effluent. Having visited the farm a few times, Aaron was happy to take advice from Nevada Effluent Management Specialist, Michael Prestidge.

“Aaron’s goal was to have an efficient system that minimised labour and maximised flexibility in when we could apply effluent fast. We worked through all the options to come out with a solution that suited the new farm’s operations,” Michael says.

The first consideration was storage. A large HDPE lined pond was the best option to be able to store plenty of effluent over wet periods when spreading isn’t an option. A weeping wall was considered, but instead Aaron installed a double stone trap to allow organic solids to pass through into the pond.

“We considered a weeping wall but couldn’t see the point in creating two products to be dealt with, keeping the effluent liquid was easiest for us.”

From there a powerful Nevada electric stirrer gets the pond well mixed before a Sabre progressive cavity (PC) pump (which is big enough to handle expansions) pumps the effluent out to a Greenback Magnum travelling irrigator.

“It’s [effluent management system] very efficient. Much less work than we thought. We just run the stirrer for around 10 minutes before pumping and it gets a good mix. It certainly grows grass!” Aaron says.

More? Visit www.nevada.co.nz

Nevada technology has been incorporated into the new dairy shed and effluent management system on Aaron Waite’s dairy unit.

MAKING SAVINGS ON WATER USE

THE CLEARTECH EFFLUENT

treatment system is giving farmers up to 70% saving in fresh water use in farm dairy yard wash-down water, helping them to meet water use consent conditions and make savings on water pumping costs.

The system, developed at Lincoln University in conjunction with Ravensdown has been installed on farms in both the North and South Islands and works by clarifying effluent through an intank, automated process.

A coagulant, ferric sulphate, commonly used in drinking water treatment, causes the solids in the effluent to settle out, allowing clarified water to be piped off and stored for use in yard washdown.

The coagulant not only settles out the solids it also helps kill the Eschericia coli (E. coli) bacteria by interfering with its cell membrane.

Lincoln University emeritus Professor Keith Cameron and Professor Hong Di have published studies showing 99.9% reduction in E. coli levels in the clarified water and a 91% reduction in the settledout, treated effluent.

Neil and Margaret Campbell’s, 800cow Thorneycroft farm near Geraldine in Canterbury has been able to cut its freshwater use for yard wash down by 67% from 26,611 cubic meetres/year to 7870 cu m/year.

On a per cow basis that’s equivalent to a drop from 105 litres/cow/day to 35 litres/ cow/day. ClearTech was retrofitted into their existing effluent system by adding a mixing tank, a clarified water storage tank and installing a coagulant tank and controller, plus a sump pump.

That’s cut their effluent volume by 60%, effectively increasing their storage capacity.

It’s also allowed them to delay the start date for irrigating effluent on to paddocks by 22 days.

The number of effluent irrigation runs needed per year has been more than halved too, dropping from 146/year to 58 runs/year.

That’s meant time spent setting up and managing effluent irrigation has dropped from 292 hours/year to 116 hours.

Valuable nutrients aren’t lost through the treatment process and in fact, recent research has shown that phosphorus (P) losses through leaching can be reduced – meaning more P is available for plant growth. Iron from the coagulant and phosphate in the effluent react to form more stable iron phosphate compounds in the treated effluent which become plantavailable at a slower rate.

While P is most commonly lost to water through the movement of soil it can also be lost through leaching particularly under effluent areas – and research has shown this can be six times greater than other areas on the farm.

Studies found P leaching losses from the treated effluent were cut by up to 99%.

Emeritus Professor Keith Cameron and Professor Hong Di have published studies showing 99.9% reduction in E. coli levels in the clarified water and a 91% reduction in the settled-out, treated effluent.