Recycled water proves fruitful for greenhouse tomatoes

n the driest state in the driest continent in the world, South Australian farmers are acutely aware of the impact of water shortages and drought. So, when it comes to irrigation, knowing which method works best is vital for sustainable crop development.

Now, new research from the University of South Australia shows that water quality and deficit irrigation schemes each have significant effects on crop development, yield and water productivity – with recycled wastewater achieving the best overall results.

Testing different water sources on greenhouse-grown tomatoes, recycled wastewater outperformed both groundwater, and a water mix of 50 per cent groundwater and 50 per cent recycled wastewater. Continue reading

Does irrigation increase the storage of carbon in soil under temperate managed pastures?

Scientists at Plant & Food Research, Lincoln University and Manaaki Whenua – Landcare Research have conducted a study on Lismore silt loam soil collected from a dryland lucerne (Medicago sativa L.) pasture on the Ashley Dene Research and Development farm in Lincoln, Canterbury.

Their main objective was to measure the effect irrigation has on the distribution of photosynthate carbon (photosynthesis derived-carbon) within the plant-soil system. This study was motivated by the lack of data available on this subject from grazed pastures in temperate climates.

The growing demand for meat, wool and dairy products has resulted in increased use of fertiliser and irrigation to enhance pasture production.

Understanding the responses of soil organic carbon to these pasture management practices is needed to assess their role in contributing to or mitigating further increases in atmospheric carbon dioxide concentrations.

Reporting on the Lincoln research, Plant 7 Food says continuous non-radioactive isotope 13-carbon dioxide (13CO2) pulse labelling of temperate perennial ryegrass (Lolium perenne L.) and white clover pasture (Trifolium repens L.) was applied to two treatments that simulated irrigated and dryland management.

The researchers observed no differences in accumulation of new photosynthate carbon (13C) in soil between the irrigated and dryland treatments – despite the irrigated treatment having significantly increased above-ground pasture productivity and reduced root biomass.  However, the irrigated treatment had reduced 13C in rhizosphere soil, and increased 13C in the 53–250 µm and < 5 µm soil size fractions compared with the dryland treatment.

These results indicate the importance of the scale at which soil processes occur, and can be used to improve models to predict more accurate soil organic carbon cycling under temperate managed pastures.

This research was funded by the New Zealand Government to support the objectives of the Livestock Research Group of the Global Research Alliance on Agricultural Greenhouse Gases.

Journal reference:

Carmona CR, Clough TJ, McNally SR, Beare MH, Tregurtha CS, Hunt JE 2020. Seasonal irrigation affects the partitioning of new photosynthate carbon in soil. Soil Biology and Biochemistry 143.

Source:  Plant & Food Research

Lincoln researcher finds soil assumptions are not holding water

Assumptions around the soil information for some Canterbury soils may need to be rethought, research by Lincoln University PhD student Balin Robertson indicates.

Balin said stony soils are used extensively for irrigated agricultural purposes, especially in Canterbury.

His results imply that soil water storage in these soils may have been under-estimated, with potential implications for efficient irrigation and nutrient management.

He said previous assumptions about how water is stored in these soils is wrong.

“They may be capable of storing slightly more water than previously thought.”

“We had assumed water retention in stony soils is only from the fine earth between the stones. But on average, stones accounted for around 10% of water retained to a depth of 60 cm in Canterbury stony soils.” Continue reading

Researchers pour cold water on ideas about irrigation efficiency

Increasing the efficiency of irrigation – it seems – may not save water as common sense suggests it should.

In a Policy Forum published today in Science [open access], Australian and international experts argue that increasing efficiency simply results in more water being used on farms and less being returned to the environment.

The Science Media Centre has asked experts to comment on the article.

The results are reported HERE.

Dr Leanne Morgan, Senior Lecturer (Groundwater), Waterways Centre for Freshwater Management, University of Canterbury, comments:

“This article argues that higher irrigation efficiency does not necessarily equate to water being ‘saved’, as is often assumed. Rather, the article argues, improved irrigation efficiency at the farm scale can lead to increased water use at the basin scale.

“Additionally, the authors argue that improved irrigation efficiency can have a range of unintended consequences. One of these is reduced groundwater levels from reductions in return flows (i.e., reductions in irrigation water moving through the soil zone to groundwater). In New Zealand, there is some evidence of reductions in groundwater levels in parts of the Canterbury Plains arising from a change from low efficiency border dyke irrigation to high efficiency sprinkler irrigation.

“The reduced groundwater levels can impact spring flows and require farmers to lower wells (at considerable cost) to access the now deeper groundwater. Managed aquifer recharge is being considered as a means of augmenting groundwater levels, again at considerable cost. This is an example, additional to those provided by the authors, of the unintended consequences that might arise from irrigation efficiency initiatives designed to reduce water use.

“The authors have outlined five steps designed to assist policy makers assess whether irrigation efficiency measures are in the public interest. These five steps focus on water accounting, caps on water extractions, risk assessment, cost benefit analyses and behavioural economics. It is interesting to note here that the five steps do not explicitly consider the relationship between irrigation and groundwater quality in any detail.”

Dr Brent Clothier, Principal Scientist, Plant & Food Research; Editor-in-Chief, Agricultural Water Management, comments:

“Paradoxically, the increasing drive to increase irrigation efficiency has not saved water. This paradox is discussed in recent paper in Science which is led by researchers from the Crawford School of Public Policy of the Australian National University. The team of authors, from a range of global institutions, are all world leaders in water-resource management and policy.

“Irrigation efficiency (IE) is simply a ratio of the beneficial use of water on the farm, to the total amount of water applied by the farmer. It’s a dimensionless ratio. Nature doesn’t deal in dimensionless quantities. Nature ‘feels and lives’ by quantities – the litres of water. That’s just the denominator of efficiency – the litres of water applied. Not the ratio.

“The IE paradox is that any water saved by the individual farmers does not – global empirical evidence shows – serve to reduce water takes across the entire catchment. More people end up using the water. So, individually, the farmers might well use water efficiently but in sum the total extraction of water by the whole community of farmers across the catchment is not reduced.

“That’s the IE paradox. What’s the solution?

“There must be robust water accounting and water-take measurements. Our Resource Management Act demands there be telemetered measurements of water takes. That’s great!

“The next step in the solution is the hard one. The authors of this Science paper state that there must be a ‘cap on extractions, an assessment of uncertainties, a valuation of trade-offs, and a better understanding of incentives and behaviours of irrigators’.

“To protect our global water resources, the world’s policy people and regulators need to grasp that nettle with a strong hand.”

No conflict of interest.

Professor Troy Baisden, Bay of Plenty Regional Council Chair in Lake and Freshwater Science, University of Waikato; Principal Investigator – Te Pūnaha Matatini Center of Research Excellence, comments:

“The Policy Forum article published in today’s issue of Science highlights that commonly accepted goals of irrigation development, when translated into government policies, can lead to a counterproductive paradox. Worryingly, this paradox is embedded in the United Nation’s Sustainable Development Goals (SDGs) that drive international comparisons, as well as economic aid programmes.

“The target for water use and scarcity (SDG 6.4) focuses on monitoring and improving water-use efficiency associated with irrigation. Improved ‘irrigation efficiency’ sounds like common sense, at least when thinking about a farm. But at the scale of river catchments and aquifers, evidence has accumulated that claimed benefits of improving irrigation efficiency rarely help to ensure water is left over for amenity, ecosystem health, or downstream users.

“The reason for this is that ‘irrigation efficiency’ concept counts water that returns to streams or groundwater as waste, rather than recognising that this water has downstream benefits, which we often call ecosystem services. These benefits include supporting downstream fisheries and wetlands as well as the overall health and amenity of some the ecosystems our society recognises as most valuable – lakes, rivers and estuaries. It’s no good if greater ‘efficiency’ means less water ‘left over’ for these ecosystems, and even worse if smaller flows of water carry even greater concentrations of contaminants.

“When we read international accounts of water scarcity and irrigation, we might think they don’t apply to New Zealand. But this one does, for a number of reasons. Firstly, our drier, irrigated regions have rapidly increased the value of their agriculture and horticulture in recent decades, from dairy to wine and fruit exports. It is widely known that our freshwater available for irrigation is already fully allocated or over-allocated in these regions. Secondly, we need to consider that climate change means better growing conditions in early spring, but more demand for irrigation in summer and autumn.

“Last, irrigation development remains a political issue, with Labour and the Greens largely opposed to support for irrigation schemes in the last election, but the Government providing careful support for some through the Regional Development Fund. Water rights and ‘ownership’, as well as kaitiaki or stewardship over downstream ecosystems is another hot topic for current political debate. The impacts of water removals for irrigation, and water returned from irrigated land on downstream users and ecosystems needs to be valued, so the true costs of water use for irrigation can be considered.

“The decisions New Zealand is making now, as we start to carefully consider water scarcity, have tended to be locked in for generations in other nations. The article provides a timely five-step framework to be applied to assess whether irrigation schemes and new water allocation policies deserve government support.

“When I apply these steps to water issues we face in New Zealand, the value of water comes into focus in two areas, to offer government, councils, industry and NGOs improved clarity on irrigation policy. The first is the quantity and timing of return flows from irrigated land, as part of water that is reserved for the health of ecosystems and fisheries. Ensuring the return flows have quality criteria, and aren’t concentrated sources of contaminants matters too. Second, it could be a fallacy to keep believing that more irrigation means more production and more value. International supply chains may place greater value on the food we produce if we irrigate to maximise the reliability of our production in the face of droughts and climate change. Supply chains, as well as tourism, seem likely to also place considerable value on minimising environmental impacts.

Conflict of interest statement: Chair funded by Bay of Plenty Regional Council.

Dr MS Srinivasan, NIWA Principal Scientist – Catchment Hydrology, comments:

“One definition of irrigation efficiency used in the paper is maximising the beneficial use (i.e. water used only by the crops irrigated). This is already mandated in New Zealand as a part of the resource consent granted to the irrigator. In places like Canterbury, where the majority of the country’s irrigation happens, the regional council Environment Canterbury has started mandating that 80-100% of all applied irrigation should stay within the root zone for crop water use.

“Over the past few years, New Zealand has moved to from flood (‘border-dyke’) irrigation to more efficient spray irrigation systems that use less water to grow the same, or more, crops. However, it is also true this water saving has allowed expansion of irrigated area across the country, as has been highlighted in this paper. IrrigationNZ statistics indicates that the size of New Zealand’s irrigated area has been doubling every 12 years since 1970.

“New Zealand has already been ahead in the game by mandating metering of water takes at farm scale (for takes over 10 litres per second since 2010 and >5 litres per second since 2016). For instance, regional councils mandate measurement of extractions at the source (rivers) as well as at the delivery points (farm gates). This has been a work in progress and its real value is yet to be realised. Water metering has resulted in a large volume of data.

“While we are on the right track, we have got to go a long way in ensuring data quality and usefulness. It is necessary the knowledge gained from this data collection is communicated back to water users to ensure best use of water. Closing this loop is important for behaviour change.

“In New Zealand, irrigation efficiency is not seen on its own – just saving water or not extracting water that is not needed. It is tightly linked to water quality. For example, the good management practice guidelines by Environment Canterbury identify a good water management practice as a critical step to good nutrient management. Thus farmers are mandated to manage irrigation to not only increase efficiency but also reduce nutrient loss from farm to surface and ground waters.

“Increasingly, irrigation schemes that seek consent to extract water out of our rivers are asked to comply with and report on nutrient management practices within the scheme area.

“NIWA’s Justified Irrigation programme is addressing the core of this irrigation efficiency issue at two levels – 1. Enabling farmers to use weather forecasts to schedule their irrigation and nutrient management practices and reduce the irrigation footprint; and 2. Providing farmers an economic incentive by reducing their irrigation costs while maintaining the productivity. The environmental and economic drivers provide farmers and others a business case to use less water in achieving the same, or better, outcome.”

No conflict of interest declared.

These author comments were gathered by the Australian Science Media Centre.

Professor Quentin Grafton is a researcher at the Crawford School of Public Policy at the Australian National University. He is a UNESCO Chairholder in Water Economics and Transboundary Water Governance, is the immediate past President of the Australasian Agricultural and Resource Economics Society, Executive Editor of the Global Water Forum and Convener of the Geneva Actions on Human Water Security

“Contrary to common wisdom, increasing irrigation efficiency frequently reduces the water available for reallocation yet governments around the globe are pouring billions of dollars into making irrigation more efficient, with disastrous consequences for fresh water availability. Together with nine other scientists and economists from eight countries and seven universities, we demonstrate that increases in irrigation efficiency, in general, reduce surface run-off and groundwater recharge to the detriment of people, the environment, and our future.

“When irrigation efficiency increases, such that a greater share of the water extracted for irrigation is used to grow crops, this frequently reduces the volume of water that previously flowed back to streams and to replenish groundwater. Because this water is not consumed by irrigated crops, and therefore does not increase crop yields, it is treated as a ‘loss’ by irrigators.

“The tragedy is that these so-called unconsumed water losses to farmers are actually return flows – water that is frequently recovered and reused elsewhere in a watershed or basin. They have value. The key point, and the paradox, is this: advanced irrigation technologies that increase irrigation efficiency frequently increase on-farm water consumption and groundwater extractions and reduce return flows.”

Quentin has not declared any conflicts of interest.

John Williams is an Honorary Professor in the Crawford School of Public Policy at The Australian National University. He is the  former Commissioner of the NSW Natural Resources Commission, former Chief Scientist in the NSW Department of Natural Resources and former Chief of CSIRO Land and Water.

“Our Science paper provides five key steps to respond to the unfolding global water challenge and look at how to reverse the tide of bad policy. First and foremost, physical water accounts are needed from the farm scale to the basin scale to make transparent ‘who gets what and where’. Second, reductions in irrigated water consumption require decreases in water extractions and limits on the irrigated area.

“The other three steps to avoid a global water tragedy include: valuing water (including in-stream flows) to ensure that the public benefits of irrigation efficiency subsidies exceed the costs; risk assessments of the effects of increases in irrigation efficiency, including uncertainties over inflows and outflows; and a much better understanding of how irrigators’ actions change as their irrigation efficiency increases.”

John has not declared any conflicts of interest.

Source: Science Media Centre

EPA Chief Scientist is leaving to return to an education role.

The Environmental Protection Authority has announced Chief Scientist Jacqueline Rowarth’s resignation.

EPA chief executive Allan Freeth says she is returning to an education role (he did not specify it) where she will also continue independent analysis and commentary on issues for New Zealand.

His statement said:

During her time with the EPA Jacqueline has built up the science team, focusing on supporting other teams with the information they need to make decisions informed by science. In particular she has encouraged staff to get involved – through speaking and writing, starting with [our internal regular feature] Science Corner. She has also spread the word externally about the role the EPA plays in New Zealand.

Jacqueline’s last day of employment with the EPA as Chief Scientist will be Friday 2 March 2018. However, Jacqueline has agreed to undertake specific research/project work for EPA for up to two months after her employment with the EPA ends. The Executive Team wishes her all the best for her future work.

AgScience’s quick Google search found the announcement reported only by Stuff (here) and Radio New Zealand (here).

It was not recorded on the Scoop website, where EPA statements are usually posted.

The Radio NZ report described Dr Rowarth as the EPA’s “controversial chief scientist”.

It also said Dr Freeth would not be interviewed about the resignation.

EPA spokesperson Diane Robinson said: “We don’t have any further comment beyond the statement on our website”.

Dr Rowarth drew criticism late last year after describing irrigation as a “great boon” to the environment.

She said irrigation helped farmers remain profitable, and they then invested that money in environmental projects.

Conservationists described those comments as “bizarre”, while the government said irrigation caused enormous environmental damage.

This presumably was a reference to reasons given for a change of government policy on irrigation schemes after the general election.

The new Labour-led Government announced it was reversing the previous government’s policy of subsidising big irrigation schemes around the country.

Conservation Minister Eugenie Sage said that was because of the enormous environmental damage.

Dr Rowarth started her EPA job in October 2016.

Irrigation is a good thing – but we must not repeat the mistakes

Dr Brent Clothier is Science Group Leader, Production Footprints & Biometrics Sustainable Production, at Plant & Food Research. He reports: 

From just 17% of our global lands, irrigation around the world now provides 40% of our food & fibre.  That’s a brilliant use of our natural capital!  It’s also enabling the New Zealand economy to boom through irrigation of our pastoral lands for dairying, and also through its use with higher value land-uses.


Or is it?

What are the implications of fiddling with nature’s hydrology without due consideration of (generally foreseeable) environmental consequences? Have we learned from past lessons? Are we destined to repeat well-known mistakes?

Beyond the water-driven demise of the ancient city of Babylon, today’s poster-child of an irrigation disaster is the Aral Sea.

The National Geographic has recently commented on this here.

Continue reading

Research challenges US biofuels goals

The United States stands little to no chance of satisfying its current biofuel goals, if the climate continues to evolve as predicted by the Intergovernmental Panel on Climate Change, according to a new study by Rice University and the University of California at Davis.

The study has been published online in the American Chemical Society journal Environmental Science and Technology.

It suggests that in 40 years, a hotter planet would cut the yield of corn grown for ethanol in the US by an average of 7% while increasing the amount of irrigation necessary by 9%.

Continue reading

Lesson from the drought: Nathan Guy promotes investment in irrigation

The drought affecting much of the country emphasises the need for irrigation projects to store and distribute water, Primary Industries Minister Nathan Guy said today.

Guy issued his media statement (here) after speaking to drought-affected farmers on the West Coast and the Central North Island this week.

Water drives NZ’s economy just as much as minerals do in Australia, he said.

“We don’t have a shortage of water or rainfall in this country, we just don’t have the capacity to store and use that water in dry times. We currently use for irrigation less than two percent of the water that lands on New Zealand.

“Done properly, storage and irrigation schemes can help to better allocate water to benefit both the economy and environment.

“If current proposals are advanced there could be another 420,000 hectares of irrigated land available over time. Research from NZIER suggests exports could be boosted by $4 billion a year by 2026, which would support thousands of new jobs.

“This is why the Government is investing $80 million this year into a new Crown company to act as a bridging investor for irrigation projects. This will involve short term, minority investments to help kick-start regional projects.

The Govt has signalled plans to invest up to $400 million in regional-scale schemes to encourage third-party capital investment. It is also supporting development of suitable projects to the prospectus-ready stage through the Irrigation Acceleration Fund.

Guy said projects will succeed only if they are committed to good industry practice that promotes efficient water use and environmental management, particularly around land-use intensification.

Irrigation projects potentially could improve the flow of some rivers in dry summer months, he said.