Dilute, well-mixed dung, urine and water work well

 Here’s the message: dilute, well-mixed dung, urine and wash water applied to pasture at the right time (and in the right quantity) is very good for the farm. It grows grass. Grass produces milk. Pasture becomes more fertile and soil condition improves. The effluent stays in the root zone on your farm and if it’s on your farm it’s not causing trouble elsewhere. The “water effect” itself (from collected rainwater and wash water) has a payback effect and the added nutrient reduces up the payback period. 

These are the essential reasons for you ‘do effluent’ properly. Another important factor is to design a way to apply the good stuff with least labour, with no (or few) solids spreading chores and of course low capital cost. (Although if spending capital is going to make the job easier and more foolproof, then go that extra distance to create a simpler, more reliable and safer system.)

So here’s the challenge:

You are going to store effluent, so that you do not waste it by trying to apply it in the wet season when the pasture doesn’t need it and when irrigating effluent in the wet means it will simply get washed into streams and drains.

You are going to thoroughly mix the wash water, manure and collected rainwater that falls on the yards and the pond before you send it to the irrigator. This prevents your irrigating a ‘thin’ mixture initially which ‘thickens up’ as the pond level falls. You want the pasture to receive the same concentration of nutrient and water over all the irrigated paddocks.

You are going to spread the effluent evenly –

 to get the best value -- at the right time and in amounts appropriate to the soil moisture levels, while grass is growing.

You are going to put in place controls that allow monitoring which prevents the waste of water and nutrients; which protects pumps, pipelines and hydrants from damage, and which prevents ponding and unwanted discharges in the paddock.

This is a broad outline of what your effluent irrigation system should achieve. The next section gets down and dirty. Forgive me for having to drive the message home, but I want you to understand it.

It would not surprise me to find that you’ve bought the effluent pump first and now you’ll create your effluent scheme around that. Right? I hope not. You’re starting at the wrong end of the process, and yes, there is a process.

The starting point of the design process is reviewing your point of view. Do you want to keep this effluent on your land (for your advantage) or are you happy enough to see it slide off your property (to your disadvantage and loss)? Furthermore, do you want it to grow grass, or do you just want to dispose of it on your paddocks and hope the applied concentration doesn’t smother pasture and choke essential soil organisms? As you find answers to these questions you will see that you have already begun the decision-making design process.

Let’s assume you’re a reasonably able farmer who acknowledges that plants need water and nutrient and like it dished up to them as a dilute consistent mixture at the right time in their growth cycle. You’ll also acknowledge you want the benefits of the proper use of effluent but you don’t want the application process to be fiddly and laborious. You might be prepared to invest capital to reduce the continuous annual chore factor. 

Finally, let’s assume you realise that if effluent stays on your property doing ‘good’, then it’s not going somewhere else doing ‘bad’. These decisions lay the foundation for the new system or an upgrade of the old one.

The next step is choose the area of the farm where you irrigate this stuff. You’ll need to decide on the required area, the soil type, when in the season the soil is ready for liquid and nutrient, the potential for irrigated liquid to run off the land, and the style of irrigator that best fits the soil and your operations. And you should even consider neighbours and the houses of farm staff. Notice that we haven’t yet got to even deciding on effluent storage or pump size. To sum up this section, let’s just say we are focused on the irrigation zones and the irrigation means.

Notice that we should not apply effluent when the soil is wet and has no capacity to soak up and retain it. There is a wet and busy season at the time of calving, and if you irrigate effluent at this time it is bound to run off your land taking the nutrients with it. So if you shouldn’t irrigate in the wet, then you will have to store the stuff until the day arrives when the soil can happily hold the effluent. This is where we have another review of your view. 

A small storage pond will usually mean that irrigation will have to be fitted in more frequently and carried out onto soils with smaller moisture deficits. You will probably have to apply small amounts of effluent over larger areas whenever there is a small soil water deficit. Of course this may also be at a cold time of the year, so that while you park the effluent in the soil satisfactorily to retain it, it may not be the best time to assist plant growth. 

Your irrigation equipment must also be able to apply these small amounts of liquid.  If storage capacity is larger, you can usually wait until soil water deficits are greater; the grass is more actively growing and the effluent can be applied in larger quantities. In this case irrigation takes place at a “cruisier” time of the year, and the growth benefits are more obvious. 

So when we summarise this part we conclude that smaller storage means applying smaller amounts more frequently earlier in the season. Larger storage means you can apply larger amounts later during the growing phase of the season. There is a range of choices between these extremes, but the most important determinants are the irrigation zones and the irrigation equipment you want to use. Small nozzles may be needed for the smaller ponds and more frequent irrigation onto damper soils; larger nozzles and application amounts will probably suit larger ponds and dryer soils.

By now we are ready to ascertain the size of your storage pond and the pumping plant and we can also begin to size pipelines and draw the irrigation plan. From now on it is just straightforward engineering design where we go through all the steps.

However, there is still a lot of blindness out there: don’t close your eyes to the problems that arise from solids, sludges, solids spreading and unnecessary chores. You may forget that sludges and solids in the effluent have to be dealt with either by separating them from the mix in separators which can be active (mechanical) or passive (weeping walls, wedgewire screens). Separation is really only needed if irrigation nozzles are small. Larger nozzles on the irrigator mean you can apply all the liquids and solids together via the irrigator. This avoids having to spread solids later.

While we are on the subject, I have to mention what I perceive to be ‘the attitude’ problem. You members of the older generation want to carry on farming as you always did and often resent change. You have probably forgotten that change has sneaked into your methods without you noticing. Look at the electronics in your car (engine management, stability control, automatic braking systems, transverse engines, turbochargers) and also in your farm operations (instant tanker printouts of milk receipts, automatic vacuum pump control, electronic cup remover, electronic herd testing and mastitis detection, temperature control, vat washing, your farm computer.) So why, when you deal with 50,000L of yard wash water each day, do you wince when someone suggests automatic control to remove the chore of distributing this stuff? Or when they suggest that the electronics will protect equipment from glitches and protect you from fines? There is good value in these devices but I often see farmers trying to save money at the wrong end of the process for the wrong reasons. You have a choice: a simple-to-operate system with good controls that make the job easy and painless, or a system where you are always on tenterhooks waiting for some sort of failure.

So here’s the message again: dilute farm dairy effluent is good when it is kept on your farm, in the root zone, to grow grass. A good system will have a financial payback period, and the peace of mind factors of a good system will have a value well beyond payback.

• Stuart Reid is managing director of Spitfire Irrigation.

• This article first appeared in Getting the Basics Right 2014 issue.