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Canterbury to California; challenges for water supply and quality
I attended the second California-based International Groundwater Quality Conference in the last week of June. I gave an address on the new Spikey® technology for the detection and treatment of cow urine patches to reduce nitrate leaching. Geoff Bates and I, through our company Pastoral Robotics Ltd, have been developing this technology for the last 3 years. Attending this conference was a bit of ‘déjà vu’ for me, as I cut my career teeth as a MAF scientist in mid-Canterbury in the 1970s investigating the effects of land use on groundwater quality.
Amazingly to all non-Americans attending the conference in San Francisco (and in fact to most Americans from outside California), until very recently the State had few laws or regulations covering the extraction and use of its precious groundwater aquifers.
This situation was especially hard to comprehend given that California has in the last 15 years lead the rest of the USA it its relatively tough attitude to atmospheric emissions from industry and transport (and in gun control for that matter, especially as far as assault rifles are concerned).
Well (excuse the pun), California has finally realised it has a serious problem, in fact a crisis, with its groundwater supply, both in terms of quantity and quality. It recently passed into law a Groundwater Act, which covers management of the 120 biggest aquifers in the State. The Act passes control of these to local authorities (vis a vis our Regional Councils), but reserves the right for the State to take over if things turn to custard. In fact, similar to what happened with Environment Canterbury a few years ago, when the government appointed temporary Commissioners.
An interesting point of difference between New Zealand and California is that while our groundwater aquifers drain slowly into the sea, being more-or-less constantly recharged by rainfall and river flow, California’s are almost all fully contained. If we used too much of ours for a period, reducing off-take will allow them to recharge relatively quickly. However, the rate of recharge of California’s aquifers is miniscule by comparison. Water-users have been extracting ever-increasing volumes of water for agriculture, industry and residential use, and now the water-tables are dropping rapidly.
Many of the large aquifers in California are now so drawn down due to increasing withdrawals and lack of recharge from successive drought years that most experts doubt that they will ever become fully recharged again. On top of this, virtually the only recharge that is occurring is drainage from agriculture, which contains nitrate and other undesirable chemicals. These have an increasingly adverse effect on the quality of the remaining groundwater.
So the race is now on to learn how best to manage both the quantity and quality of these aquifers, before it is too late. Many Californian hydrologists, agriculturalists and water-managers have visited Israel, perhaps the leading country in water-use efficiency. Heavy restrictions are starting to be applied on water use. In agriculture, a big obstacle to water efficiency is the low water-holding capacity of the predominantly sandy soils. In horticulture and some cropping, it is cost-effective to install high-efficiency drip-irrigation systems, where each plant is being delivered exactly the amount of water it needs, and no more, on a daily basis.
However, this technology is not viable for broadacre crops and pastures cut and carried for indoor feeding of animals. Restrictions on water are leading to ever-increasing numbers of Californian farmers, in particular dairy farmers, shifting to other States, particularly Idaho. An equally big problem faced by dairy farmers is the land application of manure from cow and cattle houses. Not just nitrate but even organic nitrogen gets leached into the groundwater because of the highly porous soils. And if that’s not enough, there are the high gaseous emissions of ammonia as well. Moreover, while agriculture has intensified in the vicinity of the biggest aquifers, the State’s population has increased most rapidly far away from the sources of water, requiring expensive and efficiency-sapping water transfer.
So California is up for some very difficult decisions in the years ahead. Proposals to pipe water over the Rockies – akin to bringing some of the excess West Coast rainfall over the Southern Alps to Canterbury – are mind-numbingly expensive, and almost certainly more expensive than installing desalinisation plants near Los Angeles and San Francisco. Much investigation is going into how and where to store rainfall run-off water and/or how to feed it into the most porous aquifers. In comparison, management of New Zealand’s water supply and quality – with Canterbury and the Rotorua Lakes areas being the most difficult areas – does not face anything like the same stark challenges as California’s, but it does require all of us to understand and respect the perspectives of all water-user groups to achieve optimum outcomes.
All kiwis benefit from the standard of living that our country’s huge agricultural exports bring. However, it is simply not acceptable to have streams, rivers and lakes that are not safe for appropriate recreational use, and groundwater that is not safe to drink. Fully 75% of the rain that falls on New Zealand flows out to sea eventually, providing a constant flushing effect on our waterways, lakes and groundwater. It is up to all of us to ensure that the amount of water present on the land at any one time stays acceptably pure while it is in transit. This requires both short and long-term thinking; water leached from agricultural land, and the nitrate in it, can take from less than a day to 80 years or more to reach the catchment lake, depending on location!
The dairy industry has taken the lion’s share of the blame for the deterioration in water quality, particularly in Canterbury and central North Island lake catchments. However much has been learnt and put into practice over the past decade, including fencing off waterways to prevent direct stock entry, better dairy shed effluent management, the use of riparian strips, and much more efficient irrigation technology on the 23% of New Zealand’s dairying that is irrigated.
The main problem still faced in New Zealand is the cow urine patch – the source of the majority of both the nitrate leached from the soil, and the nitrous oxide greenhouse gas (GHG) emitted to the atmosphere. The reason for this is that far too much nitrogen (N) is deposited in the urine patch for the pasture to be able to recover as it is being converted from urine-urea to nitrate in the soil. Much of the excess ends up being leached through the soil as nitrate.
One potential solution that was being touted when milk payouts were high was to house cows year-round, so that excreta can be collected and spread evenly over the whole farm. However, as well as being a long way from what kiwis identify as our ‘brand NZ’, cow housing has now been proven to simply swop one environmental problem (nitrate leaching) for another – emission of ammonia gas. Ammonia is volatilised from the houses themselves, from the manure and effluent during storage prior to spreading, and during the spreading operation itself.
The attitude in countries that rely on cow housing used to be that ‘Ammonia emissions don’t matter – it is not a global warming gas’. Maybe not, but it is now recognised as the causative agent in the fine particle smog that is so deadly to our respiratory systems. Ammonia gas attracts to it nitric, sulphuric and carbonic acid nuclei derived from industrial pollution to form these tiny (<2.5 nanometer) particles. As a result. More and more countries now require effluent plowed under or injected into the subsoil – a very expensive operation either way.
Another longer-term solution under investigation for New Zealand is the breeding of pasture and forage plants that contain lower protein levels, that better match dietary requirements, meaning there is less excess N being voided in the urine. The big challenge to overcome in this plant breeding is to ensure that yields and therefore farm production and profitability do not suffer. There is scope for genetically-modified grasses to achieve this, but again is that what kiwis want for ‘brand NZ’?
Other practices such as planting different species on different topographies and the use of stand-off pads to reduce the amount of time cows spend on the pasture can provide some benefit, but add additional management costs and require additional skills. Improved irrigation efficiency is a big help in drier areas, but nitrate still gets leached in the wetter months or in unseasonal rainfall events.
So my money (literally) is on a combination of two new technologies I have been involved in developing. Both of these can easily be incorporated into dairy farming as practised in New Zealand, with little additional time input and a net increase in farm profitability.
The first is the one I mentioned at the start – the Spikey® urine patch detection and treatment. Spikey® is a tow-behind or tractor-mounted device that is run over recently-grazed pasture daily or every second day – ie, on a ‘follow-the-cows’ basis. It detects the fresh urine patches by measuring soil electrical conductivity and simultaneously treats them with ORUN® spray. ORUN® contains tiny amounts of the totally safe urease inhibitor nbpt (the same product used on SustaiN and N-Protect granular urea). This keeps the urine-urea present in that form for a few days (before breaking down to plant-available P and N), enabling it to spread laterally by itself. This spreading creates an average 70% increase in the size of urine patches. This in turn increases pasture production, by 5-10% overall by our estimates, and reduces both nitrate leaching and GHG emissions. The addition of the growth promotant gibberellic acid to ORUN® further improves the response.
This increase in pasture production easily covers the entire costs of the use of Spikey®. After
very successful trialling of the Spikey® pre-production prototype funded by the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC), the first farm-scale versions are being built. Various research organisations are comparing the effectiveness of various alternative sprays, to see if anything is superior to ORUN®.
An automatic spin-off from utilising more of the urine-N by increasing the size of the urine-patches is that less input of fertiliser N is needed to maintain any given level of farm production. There is no magic in this; it is simply a result of ‘tightening the N cycle’, akin to repairing cracks in a swimming pool so that it doesn’t need to be topped up so often.
Reducing N inputs even further is the specific objective of the second technology, called ONEsystem®. The system uses wetted prilled urea treated with the same inhibitor nbpt used on improved granular urea products SustaiN and N-Protect, but it achieves a further 50% or more improvement in effectiveness; meaning an average doubling in effectiveness compared to granular urea. One of the key reasons for this is the vastly better coverage achieved. ONEsystem® delivers 10 particles per unit area for every one of granular urea. These much smaller prills provide a far more consistent supply of N to each pasture plant. And, unlike urea solution (urea dissolved in water), the N in ONEsystem® is not susceptible to the ammonia volatilisation losses which limit the effectiveness of urea solutions.
Furthermore, unlike other non-granular ureas, the preparation and application of ONEsystem® requires no pre-handling or highly specialised equipment. It just needs spinning discs capable of accurately spreading the much reduced N application rates that are needed to achieve the same yields, and a simple spray system to wet the prills with nbpt solution during spreading.
Farm-scale trials using both technologies are planned for this spring. Reductions of 50% in both nitrate leaching and fertiliser N inputs at current levels of production are anticipated where the two technologies are used together. Both operations will be able to be done in the same pass.
I have been very proud, and humbled at the same time, to be told by many farmers over the years that my efforts in bringing products like RPR and SustaiN to the market, and making a stand on issues such as superphoshate quality, phosphorus run-off, cadmium levels in superphosphate, and nitrate leaching are widely respected. The Spikey® and ONEsystem® technologies are simply the latest developments in my ongoing endeavours to keep improving farm profitability while protecting the environment. I hope I have learnt to be a bit more patient!
Pasture plants need to take up 7 kg of sulphur (S) for every 10 kg of phosphorus (P). So, if both nutrients are being applied in reasonably efficient forms, a fertiliser containing 9% P should only need to contain 9×0.7 = 6.3% S. Near the coast, where there is significant input of sulphate in rainwater, the amount of S required is less or even zero.
But most people know that single superphosphate or ‘super’ contains 9% P and a fixed 11% S, almost twice the calculated amount of S required. Furthermore, in higher rainfall areas and low-medium P retention soils, even this amount is insufficient, and super has to be amended with elemental S to make sulphur-super. Why is this? It is simply because much of the sulphate-S gets leached from the soil before it can be used by the pasture (taking valuable cations such as calcium, magnesium and potassium with it). Even though 10-35% of applied soluble P becomes fixed in progressively unavailable forms in our soils, this is still more efficient than is sulphate-S, except in very dry conditions.
The science of S fertilisation
It has been known for decades that, except in very dry conditions and on very high P retention soils, finely ground elemental S is far more efficient than sulphate -S. This is why elemental S rather than say gypsum (calcium sulphate) is added to straight super if more S is required, and elemental S is the ‘go-to’ product for adding to the likes of TSP, DAP and MAP.
It is no surprise therefore that by far the most common blend of RPR and elemental S sold by Quinphos was 92% RPR and 8% fine elemental S. With 12.7% P in the RPR, which also contained about 0.8% S as sulphate, this gave a product containing 8.7% S and 11.7% P ; an S:P ratio of – you guessed it – 0.7 to one.
A big proviso is that the elemental S used has to be truly fine – mainly less the 250 microns and all less than 500 mm. This can be irritating to the eyes if not dampened. These days, the cost of prilling molten sulphur with bentonite clay is far less than it used to be. These small water-dispersable hemi-spherical prills contain hundreds if tiny sulphur particles in each prill, which disperse easily in the soil.
The only situations where sulphate is likely to be needed are on extremely low rainfall areas or in cold late winter/early spring if soil S levels are low. Sulphate of ammonia provides a good N boost and takes care of the S requirement in the latter case.