Slurry is difficult to dispose of and poses a threat to people, livestock and the environment. A system operated by Andrew and Liz Williams uses slurry as nutrient-rich organic fertiliser that is cheaper than commercial products. Lloyd Phillips finds out more.
South African dairy and piggery operations produce thousands of tons of nutrient-rich slurry every year. In many cases, this remains in designated dams and is never used. Eventually it becomes an eyesore and environmental hazard when the dams begin overflowing into freshwater streams, dams and groundwater resources.
At the same time, these pig and dairy producers spend tens, and even hundreds of thousands of rand annually on inorganic fertiliser for pasture and fodder crops. With the price of fertiliser linked to the international crude oil price, input costs have increased dramatically in recent years in line with the crude oil price.
Meanwhile, profit margins of local agricultural enterprises have been declining, and farmers must continually seek ways to become more efficient – in a nutshell, by reducing inputs and producing more.
The US has implemented strict controls for the handling, storage and disposal of animal waste products in an effort to reduce the negative impact on the environment. Studies conducted by the US Department of Agriculture found that, on average, a 450kg lactating dairy cow produced just over 36kg of waste per day, a dry cow of the same weight just over 37kg, and a heifer 38,5kg. Pigs, on the other hand, excreted from 9,3kg to 28kg of waste each per day depending on age, sex and activity level.
The Agricultural Waste Management Field Handbook of the USDA found that approximately 50% of a dairy cow’s daily waste was excreted in the milking parlour and holding area, and that American dairies used an average of least 45,5 litres of water per cow per day to flush this waste into slurry dams. A herd of 100 milking cows would therefore require a minimum of 4 550 litres of water a day. The nutrient content of slurry dams varies from farm to farm depending on factors such as water content, quantities of solids, the variety of solid matter (dung, straw, waste feed, organic and inorganic matter), and the types of feed given to the animals.
Farmers wanting to use slurry as a cheaper supplementary source of plant food on pastures and fodder crop fields must first determine the nutrient content. The best way to do this is to have samples of the slurry tested in a laboratory.
Using slurry as plant food
Andrew and Liz Williams of Rosetta in KwaZulu-Natal own and operate a business, Slurry Tech, that offers dairy and pig farmers the opportunity to spread their slurry dam contents efficiently on to fields – thereby not only solving slurry disposal problems, but also saving thousands of rand on inorganic fertiliser. “Many farmers have previously not used their slurry effectively as a fertiliser for crops and pastures as they have not had the correct equipment,” says Liz. “Pumping the slurry into tractor-drawn tankers, which must then drive to the fields, spray the slurry onto the fields, and then travel back to the dams for a refill, has been too expensive to be worthwhile.”
Slurry Tech owns the only umbilical slurry pumping and application system in South Africa. It is not only a more cost-effective method of getting slurry onto crop and pasture fields, but does away with the time and effort of applying the slurry to the fields by other methods. Consisting of a high-powered slurry pump, a 1,5km umbilical hose and a tractor- drawn slurry applicator, the system is fully supplied and operated by Slurry Tech. The farmer only has to provide the diesel and pay R13,00/m3 of slurry applied.
Tests of the nutrient quality of samples from various farm slurry dams, conducted at the Soil Fertility and Analytical Services of the KZN Department of Agriculture and Environmental Affairs, show that slurry contains a wide variety of plant-beneficial
macro- and micronutrients. “There are varying quantities of carbon, sulphur, nitrogen, calcium, magnesium, potassium, sodium, zinc, copper, manganese, iron, phosphorous, and aluminium in each of the samples from different slurry dams,” explains Andrew. “By comparing their slurry’s nutrient values to the required quantities of nutrients recommended by soil sample tests, farmers can calculate how much less inorganic fertiliser they will need to reach the recommended levels. Not relying solely on expensive inorganic fertilisers to meet the soil tests requirements
will save farmers a lot of money.”
Table 1 shows a price comparison conducted by a well-known fertiliser company between the combined use of slurry and inorganic fertilisers and the sole use of inorganic fertilisers to meet soil requirements. The study showed that, at current costs, farmers could save approximately R515/ha on their nitrogen:phosphorous:potassium requirements by combining slurry with inorganic fertiliser on pasture and forage crop fields.
Slurry Tech says that for it to effectively extract slurry from a dam, farmers must ensure that their dams are properly built. According to Liz and Andrew, the ideal design for a slurry dam that provides part of a farm’s fertiliser needs would incorporate a gradually sloping bottom that channels the solid animal waste down into a corner approximately 6m deep. “This is because when we are pumping the slurry from a dam onto the fields, we don’t want to extract water only,” explains Andrew. “A properly designed slurry dam allows us to draw both solids and liquid from the deepest point in the dam, and then overnight the remaining
solids in the dam will slowly slide down to the deepest point in preparation for the next day’s application. Therefore, no valuable solid waste is left in the dam.”
Andrew adds that the time between applying slurry to a pasture and allowing cows to graze the fields again varies from three days to as long as two weeks, depending
on irrigation and rainfall levels and whether it is summer or winter. The sooner the applied slurry is washed off the grass and into the soil, the sooner the animals can begin grazing again. — Lloyd Phillips
Contact Slurry Tech on (033) 267 7677 or 082 932 0481, e-mail [email protected]. Website www.slurrytech.co.za.
Contact Soil Fertility and Analytical Services, KZN Department of Agriculture and Environmental Affairs at (033) 355 9448/9515 or fax (033) 355 9263. |fw