E uent

Dealing with effluent solids

By Logan Bowler

Solids management for some farms is a bit hit-and-miss. I see farms that have extremely poor systems resulting in troublesome FDE irrigation, and I also see some farms that have solids management overkill.

So, what’s the right system for your farm? That comes down to what volume of solids are generated on your farm – does the farm have a feedpad or not, and how is the liquid FDE system set up on-farm?

If the farms FDE system gravity feeds all FDE from the shed to the pond and then liquid FDE is pumped from the pond, there will be considerably more solids put into the pond than a farm that has a sump before the pond and irrigates fresh FDE to pasture on most days the soil conditions allow. On these days the solids are all suspended in the liquid and are put back on the paddocks.

If half the days per season were irrigation days (soil conditions are good for FDE irrigation) then the farm storage is only capturing half the annual solids generated. If the farm is on low-risk soils, then as many as 80% of the days could be irrigation days. If you paid for a solids separator or a stirrer to manage solids in the pond, then it doesn’t have a lot of work to do.

On small farms the capital cost of FDE systems can be extremely large when compared to large farms, and the costs are compared on a per cow basis. We need to be thinking smarter than just throwing more money at the system.

On our 250-cow farm at home, we have a feedpad that is predominantly used over winter. All solids are scrapped into a weeping bunker, where most of the solids are held back, and a large portion of the liquid migrates through the slats to be pumped into storage.

The dairy shed effluent gravity feeds to a sump and then from there is either pumped up into the pond or irrigated fresh. When we want to remove effluent from the pond a valve is opened and effluent gravity feeds from a pipe 200mm above the floor of the pond into the sump then pumped to the irrigator.

We have no solids separation for the dairy shed FDE. We are on high-risk soils so store much more effluent than a similar farm on low-risk soils. We have no stirrer on our pond and our pond is now five years old.

We have not seen a build-up of solids in the pond to the point where it is impacting storage volumes and we have no crusting. When solids build up to a point that they are impacting on storage volumes, we will get a contractor in to stir the pond and pump it out. In my mind, this system costs significantly less, has less repairs and maintenance, has lower running costs and is simple.

Unstirred ponds should have slightly lower greenhouse gas losses and any phosphorus held in the sludge will not diminish over time, so while there might be a delay in getting the phosphorus onto the paddocks, there are no losses from storage.

Basically all the potassium stays in solution in the liquid, so there is no delay or losses there and for nitrogen (N), a significant proportion has stayed in the liquid so that portion of N is still going back onto pasture regularly with irrigated FDE.

Regardless of whether the pond is stirred or not, in my opinion a stirrer in the sump is a must. It helps to prevent troublesome solids building up in the sump, which can then create irrigator blockages. Small (less than 1kw) submersible stirrers do a fantastic job in an average 20m3 sump and are cheap to run.

If your farm generates lots of solids, then often the most cost effective way is to separate solids before they are added to the storage pond.

If you’re not generating lots of solids, then think seriously about whether you need the additional cost of your own stirrer. It could well be that periodic stirring from a hired PTO stirrer might manage solids in the pond, or it could be done much less frequently by a contractor.

Just because a salesperson wants to sell you a solids separator or a stirrer does not necessarily mean you need one on your farm. Make an informed decision and use your hard-earned capital where it’s needed most. n

If the farm generates lots of solids then often the most cost effective way is to separate solids before they are added to the storage pond.

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Logan Bowler is the owner of Agblution Solutions Ltd offering common sense, independent advice on effluent systems. Not being affiliated to any company or any product allows him to offer completely independent advice. He and his wife own and operate a dairy farm at Marton so understand and experience effluent management on a daily basis at home.

Keep nutrients cycling

By Bala Tikkisetty

Spring has sprung and with it comes an increased risk of nutrients leaving farms due to high rainfall, low pasture growth, lots of stock urine being deposited, soil compaction and pugging.

That has the potential to impact farm production and damage the health of waterways and groundwater.

Handling those risks smartly, thereby boosting production while protecting fresh water, is what good nutrient management is all about.

Good nutrient management will keep nutrients cycling within the farm system and reduce losses to the environment to the bare minimum.

Some nutrients are more prone to loss than others, depending on the nature of the nutrient, soil type and climatic conditions.

Leaching through the soil – one of the biggest nutrient loss risks – can see the loss of the likes of nitrogen (N), potassium, calcium, magnesium and sulphur.

It occurs when water washes soluble nutrients through the root zone into deeper layers of the soil and they become inaccessible to plant roots. The leaching risk depends on various factors such as soil type, total rainfall, extreme weather events and the actual quantity of soluble nutrients present in the soil.

Don’t oversupply the soil with such types of soluble nutrients, especially not during winter and early spring, as there is a very high risk of these getting washed out through the soil and lost from farm systems.

A good understanding of the processes and terminology involved with nutrient cycles is important for budgeting and management.

For N, one of the key nutrients that both grows grass and can harm waterways, there are two important processes: immobilisation and its opposite, mineralisation.

Immobilisation is the conversion of plant available N into organic forms. Mineralisation is the conversion of soil organic N into plant available forms such as nitrate and ammonium. These processes are controlled by microbes and the degree of their activity in the soil.

Another point about N is that generally there will be an increase in nitrate leaching with increasing rates of nitrogenous fertiliser.

Phosphorus loss on the other hand, mainly occurs from erosion and runoff. Research has revealed that phosphorus losses will be high in soils with high Olsen-P levels, and also on steep to rolling country. Managing these optimum levels and controlling soil erosion are keys to helping prevent this.

The ongoing challenge is to ensure our farming systems efficiently cycle nutrients. Smart nutrient management practices for all land uses and activities has the potential to bring about substantial improvements in the quality of our water resources and profits. n

Waikato dairy farmer Rod McKinnon discusses dairy effluent and soil health with Waikato Regional Council sustainable agriculture advisor – technical Bala Tikkisetty.

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Bala Tikkisetty is a sustainable agriculture advisor at Waikato Regional Council.

Plan for effluent storage

Investing in effluent storage is a significant decision on-farm, so it’s worth taking the time to carefully plan what is needed to ensure the right design for your farm.

Current and future considerations

The first thing to consider when planning effluent storage is to think about how you currently farm and whether anything will change in future.

For example, if you’re currently an owner-operator but are planning to step back and get a manager, will that affect your plans? Or if you’re planning to expand your farm or herd – will the effluent storage pond be future-proofed to cope with those changes?

An effluent system can be tailored to suit a farm’s requirements. Let your system designer and installer know your needs during the initial design discussion and keep your effluent system as simple as possible – this makes it easy for staff to understand and manage.

DairyNZ has a farm dairy effluent systems planning guide with a table of options to share with your designer, see dairynz.co.nz/environment/on-farmactions/effluent/

Choose an accredited designer

Designing and installing farm dairy effluent systems is a technical job requiring specialist knowledge.

As with a number of trades, an accreditation system is in place for effluent design.

Accredited providers are trained effluent system specialists who understand and follow the Farm Dairy Effluent (FDE) Code of Practice and design standards when designing and installing systems.

DairyNZ established the accreditation programme. Look for the green tick logo when selecting a dairy effluent system company. A full list of accredited FDE companies is available online at effluentaccreditation.co.nz

Gather your core information

When planning effluent storage, work with your designer to create one that’s suited to your needs and property. Some things to discuss and provide information on include: • consent requirements • soil type (soils can be either high or low risk for effluent application) • daily water use in the farm dairy • your budget • your farm management and how you want to apply effluent • the pond site – including distance from the cow shed and line of sight to houses • your preferences for the storage type • effluent solids management • safety management • siting the electricity connection.

To ensure that everyone is clear, check that the quote includes key requirements above such as the site, pond type, storage capacity and electricity.

Calculate how much storage is needed

Your designer can calculate how much effluent storage is needed, based on factors including location, soil type, effluent application, shed type and water use.

A report can show you how this figure was calculated – regional councils usually prefer to see the calculation to ensure the storage meets regional rules or resource consent conditions. Some councils will only accept system design and storage calculations from an FDEaccredited company.

It’s a good idea to have a little more storage than your calculations show. The Dairy Effluent Storage Calculator will give the best results on-farm by allowing for deferred irrigation and ensuring you don’t run out of space.

If you want an independent storage calculation, an FDE-accredited company that is not a product supplier or a Dairy Effluent Warrant of Fitness assessor can provide this service – see effluentaccreditation.co.nz and www. effluentwof.co.nz

Training your team to use your new system

Ask your designer or installer for an operations and maintenance manual for your new system. They may also offer your team training on using the system.

It’s important to check the guide. n

There are a number of things to consider when designing an effluent storage pond so should be planned carefully.

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DairyNZ has summarised the key things to think about when planning or upgrading an effluent system, visit dairynz.co.nz/ effluent

Achieving your stirring goals

A shore-mounted pond stirrer will get the entire e uent pond swirling by creating a horizontal thrust, which is more effective in keeping solids in suspension.

By Lloyd Thomas

Trying to decide between a fl oating vertical shaft pond stirrer and shore-mounted pond stirrer? We’d 100% recommend shore mounted every time – and we’ve got the science to show you why.

When investing in a stirrer you want something that’s going to get the job done as e ciently and effectively as possible, otherwise what’s the point? So the fi rst thing to keep in mind is what you want to achieve from stirring:

The aim of stirring your e uent is to keep solids in suspension ready for pumping out.

Why? Because there are several unwanted issues that occur if you allow solids to settle: • Accumulation of solids can lead to blockages in your pump and/or irrigators. • Nutrients lose value when solids are left to settle in the pond. • E uent storage capacity is reduced, which can impact on council compliance. • You end up creating an additional job in cleaning out the pond with a slurry tanker or getting a contractor in to dig it out.

This leads to why we recommend shore-mounted or PTO pond stirrers over fl oating vertical shaft stirrers, because they are far more effective in keeping those solids in suspension for the entire e uent pond.

To create a stirring action that will get the entire pond swirling, you need to create a strong horizontal fl ow of water with su cient velocity to carry the suspended solids. A consistent speed of approximately 0.8 metres per second will stop solid particles from dropping out of suspension, and the only way to do this is by creating a strong horizontal thrust. This is where a shore-mounted electric stirrer is recommended as they are able to provide the right combination of angle, power and speed to churn up the entire pond.

In the past, fl oating vertical stirrers were promoted for having low power requirements, however, these are not recommended for the following reasons: • Having a vertical shaft, the solids are merely pushed away from the propeller and will then slow down and drop out of suspension in the water, so they never end up being effectively mixed. • Moving the stirrer around the pond will only shift the solids from one area to another, so nutrients are not getting mixed in and therefore don’t end up leaving the pond. • While some fl oating e uent stirrers may have low power requirements, a lot of the time these need to be run

constantly to achieve any results. • In terms of safety, it is always better to keep electricity out of water and not have the need for anyone to venture out onto an e uent pond should the stirrer require maintenance.

Another option which has been suggested in the past is using a pump type stirrer. In theory these stirrers should work, however, in reality you would need a massive pump, or even several pumps to even come close to what a shore-mounted stirrer can achieve. In fact, independent studies have proven Nevada electric stirrers to be 10x more e cient than a pump type stirrer.

“In terms of safety, it is always better to keep electricity out of water and not have the need for anyone to venture out onto an e uent pond should the stirrer require maintenance.”