Knowing Your Roots

Archive for the ‘Research’ Category

Drip Irrigation: Doing More with Less

Blog 19

Most people are already familiar with drip irrigation—they’ve used soaker hoses in the garden or seen those thin tubes in greenhouses or even in orchards. However, on large-scale agricultural lands within Wisconsin, drip irrigation is rarely seen.  Since water is usually plentiful in the state, irrigation is delivered to crops with overhead sprinklers, traveling water guns or with rotating center pivot systems. This doesn’t happen in areas where water supplies are scarce.  In other grower regions – either in the U.S. or worldwide – growers use watering systems that can be controlled to only deliver the exact amount of water the plants need, via the system known as drip irrigation.

Drip irrigation was first used commercially in Israel in the mid-1900s when the advent of plastics made it possible. It continues to be a dominant form of irrigation in many arid (dry) regions where water is the most limiting factor in crop production. In the U.S., drip irrigation is found predominantly in dry agricultural regions, such as California and Florida, where hundreds of thousands of acres of high-value crops are produced using drip irrigation.  Historically, drip irrigation had been primarily used with permanent tree and vine plantings, but new research and applications have made it increasingly desirable for specialty crops, vegetables and even row crops like cotton and corn.

In Wisconsin, less than 1% of the 500,000 irrigated acres use drip irrigation (under surface drip, subsurface, trickle or other forms of micro irrigation) and much of this acreage is in small-scale vegetable production. Wisconsin growers may not face the level of water scarcity seen in the western part of the country, but as concerns over groundwater quality and quantity increase, it may be necessary to explore alternative production strategies.

Drip irrigation has been shown to allow for significant reductions in water and nutrients by better localizing applications in the crop root zone where they can be delivered only when needed by the plant. Also by creating a drier micro-climate in the plant canopy, the risks posed by plant diseases, which thrive in moist conditions, are also greatly reduced. Drip irrigation can provide additional advantages such as a precise delivery system for plant protectants without harming beneficial insects or the environment.  With these benefits, why don’t we see more drip irrigation used in Wisconsin?   Simple, the high costs of implementing this technology have limited its use, and it remains unclear if these benefits could justify its use in more humid climates with a drought-sensitive crop like potatoes.

Looking to the future where sustainable use of water resources in potato production has emerged as one of the industry’s highest priorities, Sarah Page, a UW-Madison Masters student in Agroecology and Horticulture under the direction of AJ Bussan, has conducted research trials at the Hancock Agricultural Research Station to address just those questions. She compared tuber yield, size and processing quality under standard center pivot irrigation practices and three rates of drip irrigation for commonly grown potato varieties. She found little effect of irrigation treatment and in most years and with most varieties, there were no differences in total yield or tuber size distribution. Surprisingly, the lowest water application rate for drip irrigation yielded slightly higher than the other two rates. This was likely due to increased nutrient leaching under the more heavily irrigated plots, which was supported by nitrate levels detected in plant tissues. A potential negative consequence of lowering irrigation amounts could be drought and heat stress on the tubers, which could have negative consequences for processing quality. However, when Sarah looked into this, she found little effect of irrigation treatment on reducing- sugar content – a contributing factor to undesirable dark colors when potatoes are fried.

Sarah’s research shows that it was possible to reduce water application rates by 25% without negatively affecting potato yield and quality attributes. That’s a lot! There are many steps that need to happen before drip irrigation could be economically feasible and sustainable on a large scale in the sands of Wisconsin, but it’s one more potential tool to add to the box.

For more information, contact Sarah Page at sapage@wisc.edu.

Plants, Water, and Landscapes

Blog 17When it is warm and dry, you have probably noticed that plants require a lot of water to stay healthy, but did you know that only 10% of the water a plant receives actually remains inside of it to support life processes? Plants lose the other 90% of their required water (liquid) as water vapor (gas) to the atmosphere through a process known as evapotranspiration (ET), which is a combination of water the plants emit from pores in their leaves (transpiration) and water that evaporates from soil and plant surfaces.  ET uses a tremendous amount of solar energy, and this energy use coupled to the plant water use is referred to as the water-energy cycle of a landscape. When humans alter the composition of plants across a landscape (i.e. urbanization, agriculture), they also alter the water-energy cycle.  (more…)

Water – The Critically Important Resource for our Nation’s Food Security

Blog 16

In this current blog series we have been featuring graduate student research on potatoes in Wisconsin, and so far we have covered research in plant breeding, seed production and pest management. We are concluding this student series with 4 blogs on a topic that has emerged as one of the most critical issues facing agriculture today—water.  Will there be a sufficient supply in the coming decades to maintain the productivity and security of our nation’s food supply while guaranteeing the long-term sustainability of the resource in future generations for all to enjoy?

In Wisconsin, the issue of water and its availability is particularly acute in the Central Sands region, which is one of the top five vegetable growing regions in the nation where potatoes, sweet corn, green beans, peas, carrots and cucumbers all rank near the top of U.S. production.  The foundation of the region’s productivity lies in its geological history, which began during the glacial ice age that encompassed Wisconsin over 15,000 years ago.  The Central Sands is a large and relatively flat glacial outwash plain that deposited abundant sandy soils—ideal for vegetable production—and is underlain by a deep groundwater aquifer that provides the water, vital for crop growth and productivity.

The region covers nearly 1,400 square miles and now supports 200,000 irrigated acres, but prior to the 1950s it was not farmed because there was no efficient way to utilize the abundant water supply and as such, much of the area remained undeveloped.  In the mid-1950s, however, this largely unused, resource-poor area was transformed rapidly when modern irrigation technology became available and affordable due to aluminum supplies increasing after World War II.  This raw material provided farmers the ability to build and deploy the center pivot irrigation systems that could, for the first time, deliver water to 160 acre crop fields in less than 24 hours.  This quickly transformed the regional economic landscape into a thriving specialty crop production area which now supports a $6.4 billion food production industry and generates close to 40,000 jobs within the state of Wisconsin.   (more…)

The Battle against Late Blight, From the Irish Potato Famine to the New Millennium

Blog 15

While hard to believe, the Late Blight pathogen that caused the Irish potato famine in the 1840s and 1850s and caused the starvation deaths and forced migration of hundreds of thousands across Europe, is still a major concern in food production worldwide. The fungus-like organism, Phytophthora  infestans, is aggressive and can cause disease that can rapidly destroy whole fields of potatoes  and tomatoes. This centuries old threat is still with us and causes major concerns for potato growers in Wisconsin each year!

The pathogen can be spread quickly over whole areas by wind movement of its spores from infected source plants. These are either brought into the state as already infected tomato transplants or seed potatoes or can develop locally from un-harvested tubers or crop waste that survive freezing.  Because it can spread so rapidly under cool moist conditions, Late blight is considered a ‘community disease’ that can affect both commercial growers and home gardeners alike. Crop fields must therefore be monitored   early to detect symptoms and potential disease sources.  Growers ensure that seed is disease-free to prevent the introduction of the pathogen into the fields. They control potato volunteers and nightshade weeds that may be infected in and around production fields. And, by WI state law, growers, homeowners and garden centers are required to destroy all disease sources by May 20th before the start of the growing season.     (more…)

Responsible Pest Management—A Continually Evolving Challenge!

Blog 14

Protecting precious crops from hungry insect pests has been one of the greatest challenges to farming since the development of agriculture. Until the introduction of synthetic insecticides in the 20th century, there was little that could be done. For many years, farmers lived in fear of losing their entire crop to disease or plagues of hungry insects. Almost 2,000 years ago, Pliny the Elder mentioned burning “brimstone” (sulfur) as a fumigant to kill pests, and since then a wide array of unlikely chemicals have been employed to combat crop loss, including salt, pepper, tobacco, vinegar, turpentine, fish oil, arsenic, copper, lime and many others.

It wasn’t until Swiss scientist Paul Müller developed DDT during World War II that we had our first highly effective, man-made insecticide.  Not only did DDT contribute to the dramatic increase in agricultural productivity during the 20th century, it also spared millions of people from the ravages of insect-borne malaria and typhus, and Müller was awarded a Nobel Prize for his work.  Unfortunately, in the following decades it became clear that DDT and other subsequently developed insecticides could accumulate in the environment and cause serious harm to non-target organisms, including wildlife and humans. In response, many farmers began using a variety of tactics to reduce the usage of insecticides while still controlling damaging crop pests – strategies that came to be known collectively as Integrated Pest Management or IPM for short.  At the same time, the U.S. Environmental Protection Agency began to encourage the registration of new classes of insecticides which were termed “reduced risk” and posed little or no threat to beneficial, non-target organisms.

The first class of plant-inspired insecticides to be developed were the synthetic pyrethroids, similar to the natural chemical pyrethrin found in Chrysanthemum flowers. Pyrethroids are now commonly used in household insecticide sprays and many commercial products.  But the real game-changer was the neonicotinoid class of insecticides, developed in the early 90’s and chemically similar to the nicotine found in tobacco.  Colloquially known as ‘neonics’, this new class of insecticides were safe for humans and many beneficial insects and were also extremely effective in controlling pests. On potatoes, just one extremely low dose treatment applied at planting could protect the plant through most of the growing season. With this unprecedented combination of efficacy and safety, neonics quickly became the gold standard in crop protection for potatoes and other staples such as corn, canola and soybean. As we learned in our last blog, however, this widespread use proved too good to last. Several insects, including the notoriously adaptable Colorado potato beetle, have now developed some level of resistance to neonics, and new strategies are already being developed to stay ahead of the pests.

Insecticide resistance is not the only emerging problem with neonicotinoids. Neonics are highly soluble in water and are readily taken up by plant roots to systemically protect the entire plant.  Inevitably some of the insecticide will not be absorbed and can remain in the soil, and there is potential for rainfall to leach it into groundwater.  As mentioned previously, this is not a new problem—environmental accumulation spurred the search for less toxic alternatives to DDT and its successors.

In Wisconsin, the Department of Agriculture, Trade, and Consumer Protection (DATCP) actively monitors for the presence of agricultural chemicals in our state’s groundwater to ensure that if contaminants reach the water, they remain at acceptable levels which pose no threat to human health. In 2008, DATCP added neonicotinoids to the list of chemicals it tests for in groundwater monitoring wells, and trace amounts were detected in many wells.  Currently there is no EPA standard for acceptable levels of neonicotinoids in groundwater because they pose very little threat to humans, but their presence has spurred new research funded by potato growers to determine the extent of the problem and search for possible solutions.

In the Central Sands region where most of Wisconsin’s potatoes are grown, Ben Bradford, a graduate student in the University of Wisconsin’s vegetable entomology program, is building on these findings by conducting extensive sampling of irrigation water in grower’s fields to determine the extent of neonic incursion into groundwater. In cooperation with vegetable growers, Ben has found that, although contamination is relatively widespread throughout the vegetable production region, it is currently found only in very low amounts, thousands of times below levels that would warrant action by the EPA.  Interestingly, these results have also shown that the amount of contamination detected can vary considerably from one field to the next, and from one year to the next, revealing the dynamic nature of groundwater in the Central Sands.  By using satellite imagery and advanced mapping software, it may be possible to determine some of the contributing factors to these neonic detections and to work with growers to tweak their pest management strategies to mitigate this problem. This research is yet another great example of the UW and the potato growers working together to define the extent of an emerging problem and move quickly to develop solutions.

For more information contact:

Ben Bradford: (bbradford@wisc.edu)
Dr. Russell Groves: (http://labs.russell.wisc.edu/vegento/)

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