Friday, March 29, 2024

Big impacts on effluent storage

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There are a range of factors to consider when working out how much effluent storage your farm needs but some have a bigger impact than others. DairyNZ’s effluent expert Logan Bowler talks about the significant impact shed water use and application depths have on your storage requirements.
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We're all familiar with the saying, reduce, reuse, recycle, and the same principle can be applied to water use in the milking shed to significantly slash the amount of effluent storage you need.

After taking into account your soil-type, as discussed in the last column, shed water use is the second most important factor to consider when determining how much effluent storage your farm needs.

I’m sure many of you know roughly how much water you use to clean up the milking shed but it’s a good idea to calculate exactly how much. 

On average, most dairy farms use about 70 litres a cow a day in the milking shed. Some might use slightly more or less depending on shed set up and whether you’re milking once or twice a day. 

By comparison, an interesting titbit is the average human uses about 250 to 300 litres a day. 

There are a few ways to reduce water use in the milking shed but I believe the one with the biggest impact is installing a green water washing system.

By washing your yard with recycled effluent or green water you can cut water use by up to 65%. That can cut your effluent storage requirements in half.

It could see a 500-cow farm drop water use from 23,000l/day to 12,600l and reduce the pond size from 5700 cubic meters to 2400. 

Along with reducing water use and effluent storage there are also significant electricity and labour savings. 

If we consider the above example that farm would also reduce effluent irrigation from 77 minutes a day to 42 minutes. That 35-minute saving frees up staff to do other tasks.

So, if you’re looking at installing or upgrading your effluent storage I’d encourage you to consider investing in a green water washing system. You might be surprised and find the cost is largely offset by the money you save with a smaller effluent storage pond or tank. 

Another key factor to consider is effluent application depths.

Once again, this comes back to the importance of understanding your soil-type. 

If your farm is on high-risk soils it’s a good idea to take the little-and-often approach and irrigate effluent on your paddocks whenever conditions are right – dry soil and fine weather.

Using shallow application depths of 3mm rather than 5mm and 10mm enables you to irrigate more often and reduces your storage requirements. 

I know this might sound contradictory but let me explain. 

Soil is like a sponge – it can hold only so much water before it’s either taken up by pasture or leaks into ground water. Applying shallow amounts of effluent increases the number of opportunities when conditions are ideal to irrigate. 

But, as with most things, there is a trade-off. 

While shallow application will significantly reduce your effluent storage requirements it will require more labour because you irrigate more often and through the busy calving period. So, it’s worth weighing-up whether you’d rather spend a bit more and get a larger pond, which will allow you to store your effluent and apply deeper application rates when conditions are better in spring, summer and autumn. 

Everyone’s effluent storage requirements are different and there’s no one-size-fits-all approach so if you’re looking at upgrading or installing an effluent system talk to an accredited effluent system design company to ensure you get the right system for your farm. 

MORE:

Visit dairynz.co.nz/effluent.

• Logan Bowler is a DairyNZ environmental extension specialist and effluent management expert

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