What are the key environmental parameters that impact pea yield? On the surface, the easy answer is temperature and moisture. Get them right and you get a top-yielding crop.
But what is the right combination? That’s what Rosalind Bueckert, a professor in the plant sciences department at the University of Saskatchewan (U of S) wanted to find out in an effort to better understand pea growth habits and to help improve pea breeding at the U of S Crop Development Centre (CDC).
“Pea cultivars are heat-sensitive so our goal was to investigate how weather impacted growth and yield for a dryland and an irrigated location,” explains Bueckert, who published the research in the Canadian Journal of Plant Science in 2015. “We explored relationships between days to maturity, days spent in reproductive growth – flowering to maturity – yield and various weather factors.”
Research in other countries had identified that high yield was related to early flowering, a large number of reproductive nodes and soil moisture availability during flowering. The longer the plant remained in the reproductive growth period, the higher the yield. Research had found that high daily maximum temperatures (31 C to > 34 C) during flowering for at least two to four days reduced yield due to abortion of buds and flowers, aborted young seed and potentially smaller seed. In Canada, though, the relationship between daily high temperatures, precipitation, and yield had not been explored.
Bueckert, along with colleagues Stacey Wagenhoffer and Tom Warkentin at CDC and Garry Hnatowich at Saskatchewan Irrigation Diversification Centre, Agriculture and Agri-Food Canada at Outlook, Sask., utilized the nine years of Co-op variety registration trials at the dryland Saskatoon site and the irrigated Outlook site to look at environmental effects on yield. They measured days to flowering when 50 per cent of the plants in a plot had an open flower, days to maturity, disease rating and seed size. The nine years covered the range of weather patterns with some hot and dry, warm, or cool and wet.
Check varieties in each year were utilized and represented current popular varieties. For example, in 2009 the five varieties were Eclipse, Cutlass, CDC Striker, CDC Cooper and CDC Golden. Peas were grown using recommended production practices. At Saskatoon, pea was not sprayed with a fungicide except in 2005 and 2009 when disease pressure was observed. At Outlook, pea was sprayed every year with a fungicide at flowering followed by a
second application 10 to 14 days later.
Critical maximum daily temperature
Bueckert says the length of reproductive growth was an important factor in yield, and that heat stress or lack of moisture caused flower and reproductive node abortion. Conversely, the longer the pea spent in the reproductive growth phase, the higher the yield.
“Pea was sensitive to heat but heat units did not satisfactorily describe growth and yield in all environments,” reports Bueckert. “Strong relationships were observed between crop growth and mean maximum daily temperature experienced during reproductive growth, and between crop growth and mean minimum temperature.”
The researchers found that when the mean maximum temperature was greater than 25.5 C at the dryland site, the number of days in reproductive growth was reduced to less than 35 days. More than 20 days above 28 C meant less time in the reproductive phase and lower yield for dryland pea.
“The threshold maximum temperature for yield reduction in the field was closer to 28 C than 32 C from [other] published studies, and above the 17.5 C mean seasonal daily temperature,” Bueckert explains.
At Outlook, irrigation helped to buffer the effect of heat, and the pea remained in reproductive growth for 35 to 40 days in a wider temperature range of 24.5 C to 27 C.
To put those temperatures into perspective, average climate data shows that from June to August, Saskatoon experiences 11.5 days above 30 C and Outlook 12.3 days.
“Clearly, mean daily maximum temperatures exceeding 25 C were associated with shortened reproductive phases of less than 35 days at both Saskatoon and Outlook,” Bueckert says.
Plant breeding implications
On the Prairies, late-maturing varieties take about 94 days to mature, with medium maturity varieties around 90 days and the earliest at 86 days. Yet the normal frost-free period for Outlook is 123 days and 117 days for Saskatoon. Bueckert says plant breeders could lengthen maturity in pea by at least seven days without frost risk. If plant breeders could get the pea to flower earlier and longer (more indeterminate growth), yield potential could be increased.
Nov. 2, 2015, Ontario – Climate change is making Ontario’s farmers look carefully at water conservation and efficient use.
Agriculture is a significant water user in the province, and after experiencing drought-like growing conditions in 2012 and watching regions in the United States deal with severe water restrictions, Ontario agricultural researchers are working to find new cropping methods to use water as efficiently as possible.
In Ontario, crop irrigation systems are most commonly used on fruit and vegetable crops; fewer than 5,000 acres of field corn are currently irrigated.
However, irrigation is essential to producing maximum corn yields in parts of Ontario, leading researchers and irrigation experts to team up to find new ways to irrigate crops in a more water conscious and efficient manner.
The result is a new-to-Ontario below ground crop watering system, Subsurface Drip Irrigation (SDI).
Since 2013, University of Guelph Plant Agriculture professor Rene Van Acker has led a research team studying this low-pressure, high-efficiency irrigation method that uses buried polyethylene drip lines to bring water and nutrients to crops.
The team has been testing the system in corn fields, since corn requires more inputs like water and nutrients than other Ontario-grown field crops.
“Traditional crop irrigation methods are very labour intensive with inefficient water and energy use,” says John O’Sullivan, also a professor in the University of Guelph’s Plant Agriculture department and the on-site project manager of the SDI research.
O’Sullivan explains customary irrigation systems use aluminum pipes laid above ground and across fields, using overhead water sprinklers to deliver water to crops.
Mobile sprinklers are also popular, but use a lot of energy and of the irrigation water applied, as little as 50 per cent is actually used by the crop.
“SDI can deliver water with an efficiency of 95 per cent or higher and keep corn root zones closer to optimum soil moisture and maximize fertilizer utilization,” says O’Sullivan.
The team has proven SDI is the most efficient system with water savings of 25-50 per cent when compared to traditional overhead water irrigation.
Burying the SDI water lines instead of sprinkling water onto the crops immediately boosts water use efficiency by eliminating water evaporation from above ground sun and air exposure.
Unlike other drip irrigation systems where water lines lay flat on the ground surface, SDI drip tapes are buried 14” in the ground.
Doubling the efficiency of the new irrigation system, crop nutrients, or fertilizer, can also be added to the water pumping through the sub surface irrigation lines.
This allows farmers to deliver exact amounts of fertilizer to the crop throughout its growing stages. And since nutrients are applied right at the plant’s root level, very little is left unused, which reduces the chance of fertilizers leaching into the environment.
“It’s like spoon feeding our plants,” says Gary Csoff, technology development representative with Monsanto Canada Inc., who points out the ability to apply nutrients through the SDI system also maximizes the crop’s yield, quality and the farmer’s economic investment in costly crop nutrients.
“This new crop production technology will maximize productivity per acre while protecting our environment,” says O’Sullivan, adding that a one per cent adoption rate of SDI by Ontario farmers would generate an additional $10 million in farm gate sales through increased yields and more efficient nutrient management.
SDI research has been funded by Farm and Food Care Ontario’s Water Adaptation Management and Quality Initiative.
The research team has also been awarded funding through the University of Guelph’s Gryphon’s LAAIR (Leading to Accelerated Adoption of Innovative Research) program to continue testing and conducting demonstrations to farmers interested in adopting this new technology. The Gryphon’s LAAIR is supported through Growing Forward 2, a federal-provincial-territorial initiative.
“This is an out of the box approach to irrigation that has stimulated a lot of thought and discussion,” says Csoff.
The SDI research team also received input support from Peter White, Irrigation Research Associate at Simcoe Research Station, Todd Boughner of Judge Farms in Simcoe, and Vanden Bussche Irrigation of Delhi.
Dry conditions can significantly reduce soybean yields, so a five-year project is underway in Ottawa to add drought tolerance into Canadian soybean varieties.
“Drought stress is the major abiotic constraint to high stable soybean yields in Eastern Canada. From 2000 to 2012, Ontario had five summers that were drier than the long-term average. That is one year in three with drought,” notes Malcolm Morrison, the project’s principal investigator. He is a plant physiologist at the Eastern Cereal and Oilseed Research Centre (ECORC) of Agriculture and Agri-Food Canada (AAFC).
Morrison explains the project isn’t about prolonged periods of extreme drought like the Dirty ’30s. Instead it’s about short periods of dry weather within a growing season. “This is called ‘periodic drought,’ and it can be quite dangerous for soybean yield, especially if the dry weather occurs during sensitive growth stages,” he says.
“We’ve found that the first three or four weeks after the beginning of first flower is about the most sensitive stage to changes in precipitation. If you get precipitation at that time, you will be rewarded with a higher yield. But if you get drought, you will get fewer flowers producing pods and fewer seeds in those pods, and that will affect yield.”
Along with yield reductions, dry conditions can also influence seed quality. As rainfall decreases, protein content decreases and oil concentration generally increases slightly. In addition, the seeds tend to be smaller and may be misshapen or wrinkled.
Morrison points out the ability to tolerate periodic drought is particularly important for reliable soybean production in Canada. With our relatively short growing season, a soybean plant will have little time later in the season to compensate for a reduction in seeds that has occurred due to dry weather.
Screening for multiple mechanisms
The project, which runs from 2013 to 2018, is screening non-GMO soybean lines from AAFC and Sevita International for drought tolerance. The selected lines go to the breeders for development of new and improved Canadian soybean varieties.
Many characteristics can influence how well a soybean plant does under dry conditions; some examples include a deeper root providing access to deeper soil moisture, or early vigour so the plant shades the soil surface sooner, or more efficient water use, or earlier closure of leaf pores, called stomata, to stop water loss from the plant.
“There are lots of different drought-tolerance mechanisms that can be brought into play in a plant, but those mechanisms can be detrimental to yield in a year with a lot of moisture,” Morrison explains.
He gives the example of earlier stomata closure. When the stomata are open, they allow water vapour and oxygen to escape from the leaf, and carbon dioxide to enter. So, earlier stomata closure does more than stop water loss. “If a plant closed the stomata early, then it wouldn’t have enough carbon dioxide for photosynthesis even when the drought conditions aren’t that bad. If we bred a plant like that, it would be really good in dry conditions, but not in wet conditions.”
One key drought-response issue for soybeans is that dry conditions can halt nitrogen fixation. Morrison says, “Nitrogen fixation is a symbiotic relationship between a bacterium and the plant that produces the root nodule. The bacteria that live in the nodules receive carbon from the plant and in return supply the plant with nitrogen. But as the plant responds to a dry condition, the stomata close and it stops actively photosynthesizing, it stops producing carbon, and it stops moving that carbon down to the nodules and giving the bacteria food.”
Given the complexity of drought-response traits, Morrison isn’t screening for just one or two specific traits. Instead, he is using a method that identifies the plants that “can capitalize on several drought-tolerance mechanisms to produce high yields under dry conditions and high-moisture conditions.”
For this method, Morrison supplies field-grown soybean plants with water every day and then compares the yields of those irrigated plants to the yields of the same soybean lines grown in adjacent plots that have received only natural rainfall. “This is called the Delta Yield concept because it is based on the difference between the yields of the well-watered plants and the yields of the natural-watered ones.” “Delta” refers to the Greek letter delta, an abbreviation used in science for “the difference between.”
The researchers want to find soybean lines with very little yield difference between the irrigated and rain-fed plants. “The cultivar with the lowest Delta Yield is the most drought-tolerant, yet won’t suffer a yield drag when there is no drought,” Morrison explains. “This method has been used in the United States to develop a water-use-efficient corn hybrid that yields 7.4 per cent higher in drought and 3.4 per cent higher in normal water situations.”
For the irrigated plots, Morrison uses a product called Drip Tape made by Toro. “It is a plastic tape that is buried at five inches deep. Every 30 centimetres, there is a small slit in the tape, and that leaks at a certain amount when you put water into it. On a daily basis, I give the plants between two and three millimetres extra precipitation.”
This subsurface irrigation method has a lot of advantages. Morrison says, “It saves on water; we don’t have to apply a huge amount of water to the surface. It also allows us access to the field to take measurements because the soil isn’t mucky. And it allows a fairly precise application of water; we know how much we’re putting on per area.”
From previous research, Morrison knows soybean plants respond well to extra moisture, as long as it doesn’t come all at once and flood the plants. “We’ve done experiments showing that you can get an increase in yield with up to 650 to 700 millimetres of precipitation during a growing season, if the precipitation is evenly distributed.” That amount of rainfall is quite a bit higher than the average growing season rainfall in Ontario’s soybean growing areas. For example, Ottawa’s 30-year average growing season precipitation is 466 mm.
According to Morrison, the Delta Yield approach works very well in most years, although the differences between the irrigated and non-irrigated yields are not as noticeable when precipitation is abundant, as it was in 2014 in the Ottawa region. But he adds, “Even in 2014, we still had periodic drought in the first two weeks of August. That is always going to occur, and that is why we are doing the research – we’re aiming for a plant that has the capacity to kick-start mechanisms that get it through those rough points in the growing season.”
Even though drought-tolerance traits can be doubled-edged in wet years, some drought tolerance is almost always better than none, as shown in research led by Thomas Sinclair of the University of Florida. The researchers modelled the response of soybeans with different drought-tolerance traits using 50 years of weather data for 2655 U.S. locations. “They found that, in the vast majority of times, incorporating any drought-tolerance mechanism is actually beneficial because at some point in time during the growing season you are going to have a periodic drought, even in years of abundant moisture,” Morrison says.
When he first started experimenting with the Delta Yield approach, he tested it on some old soybean varieties. “One of those was Maple Arrow, released in 1976. Maple Arrow is a watershed variety because it was the first short-season variety. It is the progenitor of all the short-season soybean varieties in Canada. Interestingly, we found that Maple Arrow had quite a low Delta Yield in a dry year, so it is inherent in its capabilities for drought tolerance.”
Morrison is making good progress in the current project. “Every year, we test 20 Sevita experimental lines and 12 Ag Canada experimental lines to try to find drought tolerance. We have found some lines that have great performance under irrigation but not very good performance under normal conditions. And we’ve found some with very low Delta Yields, which is what we’re looking for.”
He notes, “In the first year of the project, we tested a lot of foreign soybean material, lots of Chinese lines and a couple of Indian lines.” However, most of the drought-tolerance genetics they are testing originally came from U.S. soybean breeding programs, which have identified lines with various strategies for dealing with dry conditions. The breeding programs at ECORC and Sevita have been and are breeding those genetics into Canadian-adapted backgrounds for testing by Morrison. For example, Elroy Cober, the soybean breeder at ECORC, is currently incorporating genes for drought-tolerant nitrogen fixation, and Morrison will be screening those lines in the future.
Overall, this project aims to contribute to the development of Canadian soybean cultivars that have greater yield stability across all years – whether the conditions are dry, normal or wet. “This will result in greater average yields and higher profits for Canadian soybean growers,” Morrison says.
August 24, 2015 - A U.S. Department of Agriculture (USDA) engineer in Fort Collins, Colorado, is making it easier for growers to determine if their crops are water-stressed.
Agricultural engineer Kendall DeJonge is trying to conserve irrigation water by using infrared radiometric thermometers (IRT)—sensors that can determine crop canopy temperatures and subsequently detect crop water stress.Scientists interpret IRT data by using one of several indices, including the commonly used Crop Water Stress Index (CWSI). Developed in the early 1980s, the CWSI requires knowing the air temperatures and humidity levels and involves a fairly technical process.
DeJonge and his colleagues compared the CWSI with five other indices, or formulas, for interpreting IRT data to see how well they could detect crop water stress over 2 years in a corn-sunflower rotation. Two of the indices developed for the study, the Degrees Above Non-Stressed (DANS) index and the Degrees Above Critical Temperature (DACT) index, were simpler than CWSI. DANS is calculated by comparing a stressed plant's temperature to the temperature of a non-stressed plant in the same environment. DACT is based on an established crop temperature threshold, and plant water stress is determined by how many degrees the plant temperature reaches above that threshold.In the study, crop canopy temperatures were taken each day around the clock but focused on 2 p.m., when water stress levels were usually the highest. The researchers also monitored soil water levels and crop water use, and fully irrigated part of the field, while intentionally stressing other areas.
The findings showed that the DANS and DACT indices were just as effective as CWSI at determining water stress even though they require much simpler measurements - a once-a-day reading of only crop canopy temperatures.
DeJonge plans to develop "crop water coefficients" that establish water needs of specific crops under different scenarios. With that data, IRTs could soon be more widely used by farmers. DeJonge foresees farmers using handheld IRTs in the near future—and eventually using IRTs with drones to calculate water needs over extensive areas.
Aug. 20, 2015 - Every cubic metre of water delivered for irrigation creates $3 to Alberta's GDP and $2 in labour income. This is one of the key conclusions in a study funded by the Canada-Alberta Growing Forward 2 program and commissioned by the Alberta Irrigation Projects Association (AIPA).
According to a news release from the AIPA, the study also shows that for every dollar of irrigation related crop, livestock and food processing sales, total GDP increased by $2.54 and labour income increased by $1.64. Overall, irrigation contributes $3.6 billion each year to the province's GDP averaging $2,550 per acre of land irrigated. The governments of Alberta and Canada are the beneficiaries of $1.3 billion in income annually from irrigation-based economic activity.
"We have known that irrigation is the lifeblood of many communities in southern Alberta, but we wanted to be able to quantify our overall economic impact in Alberta," explained AIPA chair Erwin Braun.
Other key conclusions in the study:
- The irrigation agri-food sector contributes about 20 per cent of the total provincial agri-food sector GDP on 4.7 per cent of the province's cultivated land base.
- Almost 90 per cent of the GDP generated by irrigation accrues to the region and the province, and 10 per cent to irrigation producers.
- Using labour incomes as the criteria, 89 per cent of the irrigation-related benefits accure to the region and province, and 11 per cent to irrigation producers.
- Because of the growth of irrigation in southern Alberta, irrigated crop and livestock production has resulted in 38,000 jobs, and food processing has created another 17,000 full time equivalent positions.
- Benefits from irrigation water and infrastructure used for non-irrigation purposes, such as recreation, hydropower generation and drought mitigation generated an additional $85 million to the provincial GDP and $71 million in labour income.
"We also wanted to know the industry's economic challenges for the future," Braun stated in the news release. "And what the study shows is that there is a clear need for governments to work with industry to plan for potential impacts of climate change on agriculture, both positive and negative."
The study calls for long-term water and drought management strategies, including increasing Alberta's water storage capacity, and better communication with international markets about the environmental and economic sustainability of Alberta's irrigation agri-food production and new food production opportunities to meet growing world-wide demand.
Direct seeding has contributed to sustainable crop production. Photo by Bruce Barker.
Optimum crop production depends on inputs of commercial fertilizer, livestock manure, herbicides, fungicides and insecticides. The economic benefits of increased crop production have been very positive; however, we must also recognize potential negative ecological effects of fertilizers and pesticides.
Commercial fertilizers and livestock manure are used to increase crop yields and to replace soil nutrients removed by harvested crops. Fertilizer and manure have been essential in reversing the trend of declining soil productivity and declining soil nutrient reserves. Research across Western Canada has clearly shown that added fertilizer not only increases crop yields, but also leads to increased soil organic matter when more crop residue and root matter are returned to the soil.
With the use of fertilizers, manure and pesticides comes the increasing environmental concern over potential contamination of soils, surface water and groundwater, and even air quality. A number of new and ongoing research studies by provincial agriculture departments, universities and Agriculture and Agri-Food Canada are being conducted across Western Canada to better understand various concerns.
A number of important lessons have already been learned from research. With practical knowledge, producers can take a very proactive approach to ensure agricultural practices minimize negative effects when utilizing input products on their farms.
Nitrogen and nitrates
Nitrogen (N) in various fertilizers and livestock manure is converted by soil microbes to nitrate-nitrogen (NO3-N), the primary form of N that plants take up. Nitrate is negatively charged and is not held by negatively charged soil particles. Therefore, higher levels of nitrate in soil coupled with excess rainfall or irrigation can result in leaching of nitrate through the soil root zone and into groundwater.
Some ways to minimize the potential for nitrate leaching include:
- Soil test to determine soil nitrate-nitrogen levels; then, use the information to determine the optimum N fertilizer and/or manure application rates. Select a realistic target crop yield and apply the N to meet (similar to average) crop requirements.
- Take all sources of N into account, including N from previous manure applications, N in crop residue, N mineralization potential of your soil, and previous pulse or legume crops.
- Areas in a field that have uniquely different soil types may require different fertilizer management practices or application rates. These unique areas should also be soil sampled separately from the rest of the field and managed separately.
- Optimize N fertilizer application method and timing:
- Band or side-band N fertilizer instead of broadcast incorporation to maximize crop efficiency of uptake and minimize N fertilizer losses for annual crops.
- Apply split N fertilizer applications on hay and pasture land.
- Apply split N fertilizer applications for longer-season irrigated crops grown on sandy soils using fertigation (fertilizing through the irrigation system).
- When manure or N fertilizer is applied in fall, wait until late fall when surface soil temperature is less than 7 C to slow the release of N to the mobile nitrate form.
- Consider the use of new, slow release N fertilizer products to minimize the amount of nitrate-nitrogen in the soil and minimize N leaching potential.
Shift to direct seeding
The shift to direct seeding to minimize soil disturbance and maintain as much crop residue cover as possible on the soil surface has a number of sustainable benefits to producers and the environment:
- Reduced soil disturbance results in less rapid soil organic matter breakdown, resulting in increased soil organic matter levels and improved soil structure, leading to improved soil quality.
- Placing fertilizer with the seed and in a band at seeding puts the fertilizer well below the soil surface, which greatly minimizes potential nutrient runoff from fields into surface water.
- Improved soil organic matter levels and improved soil structure result in reduced soil moisture loss and increased water infiltration rate, which reduced water runoff into surface water.
- Improved soil moisture conditions will reduce the need for land to be summerfallowed. Summerfallowed land has a higher risk of nitrate leaching, a higher occurrence of soil salinity and a greater risk of soil erosion.
- Weed seeds are less likely to germinate and grow on the undisturbed soil surface, reducing annual weed problems and potentially reducing the need for some herbicides.
- Less fuel is needed for field operations with direct seeding, which reduces greenhouse gas emissions and is cost saving for the producer.
- Continual soil cover protects soil from wind and water erosion, which greatly reduces the risk of soil and nutrient movement into surface waters.
Effective use of sustainable crop rotations
The use of diverse crop rotations can be beneficial to combat some weeds, crop diseases and insects. Growing a range of cereal, oilseed, pulse and/or forage crops will result in the use of a wider range of herbicides from different groups, which will reduce the potential development of herbicide-resistant weeds.
Diverse rotations with different crops can disturb weed populations to help keep weed populations in check. Some diseases and insect pests can also be kept in check with more diverse crop rotations.
Always avoid growing the same crop two years in a row on the same land to minimize pest problems and reduce the need for repeated use of the same crop protection chemicals (herbicides, fungicides and insecticides).
The inclusion of legumes in the crop rotation will reduce the need for N fertilizer. The N-fixing ability of legumes generally means that little or no N fertilizer is needed for crops such as alfalfa, sweet clover, pea, chickpea, bean and lentil. In the year following an annual legume, plant-available N is added to the soil as residue breaks down, reducing the need for commercial N fertilizer. Further, N from residue is released slowly over the next growing season; therefore, there may be less risk of nitrate accumulation in soil, which may reduce the risk of nitrate leaching.
Reduced N fertilizer requirements will reduce the amount of energy needed to manufacture and transport N fertilizer to the farm, thereby reducing greenhouse gases and conserving energy.
Use livestock manure wisely
Livestock manure is an excellent fertilizer and must be viewed and managed as a resource rather than a waste:
- Soil testing is critically important to allow for good nutrient management planning. By determining nutrient levels in soil, producers can better match nutrient levels in manure and balance them with crop nutrient requirements. This practice will lead to reduced problems of nutrients entering surface or groundwater.
- When applying manure, always stay a safe distance away from surface water bodies.
There is increasing concern about phosphorus (P) from agricultural lands causing problems with surface water contamination. Phosphate leaching into groundwater is rarely an issue as inorganic soil P is normally not mobile in soil and normally does not leach significantly. However, inorganic and organic P can be carried with sediments into surface water. Water runoff from agricultural lands is a serious environmental problem. Ensuring that water erosion does not occur on farms will go a long way toward minimizing contamination of surface waters. The shift to direct seeding has played a strong role in minimizing soil erosion and movement of sediments into surface waters.
Pesticides in surface waters are of increasing concern, and routine monitoring of surface waters over the past 15 years for pesticides has indicated there are significant problems in Alberta. Fortunately, most detected herbicides have been below the current water quality guidelines for aquatic life and drinking water. But this is an issue of serious concern.
It is thought that the primary means of herbicide transport into surface waters is by water movement of sediments from fields and in some situations transport of soil particles by wind. Soil conservation efforts, such as reduced tillage and direct seeding, can go a long way toward minimizing this transport mechanism. When using soil-applied herbicides, maintain good trash cover to minimize soil erosion and water runoff from fields.
Leaching of herbicides into shallow groundwater has been identified as a potential concern, particularly on sandy soils in higher rainfall areas and on irrigated land. Leaching will occur when excess water moves through the soil before herbicide breakdown has occurred. Herbicides with the greatest risk of leaching have a higher solubility and have a longer half-life (resistant to rapid breakdown).
To minimize herbicide leaching, producers should pay particular attention to herbicide solubility and the rate of breakdown (half-life) of the herbicides they use. Select herbicides with lower solubility when farming on sandier soils with higher leaching potential. To avoid pesticide contamination of water at point source, producers should use a nurse tank to fill a sprayer to avoid the problem of back-siphoning from a sprayer tank into a water source. Herbicide spills during tank fill can also contaminate water sources. To prevent this potential problem, add the concentrated pesticide product to the spray tank at a safe distance away from a water source.
Fungicide and insecticide use have increased dramatically across the Prairies in the past decade. Repeated use will lead to greater pesticide resistant diseases and insects. There are questions and concerns about potential negative effects of fungicides on soil microorganisms. There is increasing concern with the negative effects of insecticides on beneficial insects. When we use crop protection chemicals, we must consider the potential negative effects on our soils and the ecosystem in which we live.
It is critically important that our agricultural cropping systems be complementary to maintain healthy, productive ecosystems, which are also essential to human well-being. This article is intended to stimulate thought and discussion concerning how agricultural cropping practices can be made more sustainable. With continued research and development of practical knowledge, Prairie producers can continue to take a very proactive approach to minimize potential negative effects of our industry when utilizing fertilizers and pesticides on their farms.
Society is becoming increasingly concerned about surface and groundwater quality degradation from agricultural operations. We are becoming more aware that environmental problems can occur with over-application of manure applied to land repeatedly over a period of years. Overloading soil with nutrients, poor manure handling or poor timing of manure applications can lead to contamination of surface or groundwater.
However, if good manure management practices are followed, animal waste can be utilized as a valuable nutrient resource rather than treated as a waste that becomes an environmental concern.
It is important to realize it is not possible to apply manure to match crop requirements for all nutrients. When manure is applied based on one nutrient, other nutrients will be either over- or under-applied. For example, if feedlot manure is applied to meet the nitrogen (N) requirements of a wheat crop, phosphorus (P) will be applied at approximately three to six times the rate of crop requirements, depending on the P level in manure. Repeated applications over a period of years will result in build-up of high levels of P in soil. To complicate the situation, nutrients such as N and P are contained in a number of different organic forms in manure. The unavailable nutrient compounds break down and release at different rates over a period of years.
Many producers who have applied manure to their land based on N content have noticed a gradual build-up of soil P. Many fields exceed 400 lb/ac of available P in the top six inches of soil, while some fields are in the range of 800 lb/ac of available P. This is equivalent to 1770 lb/ac of P2O5 and 3540 lb/ac of 12-51-0 phosphate fertilizer, respectively. To further complicate things, the soil test doesn’t measure the unavailable inorganic or organic forms of P in the soil. Soil tests just show the plant available fraction of inorganic P in the soil.
When soil test P is very high, it can result in reduced crop yields due to nutrient imbalances and it can interfere with plant uptake of other nutrients. Further, high soil P can result in greater potential for runoff into surface water. The USDA says one pound of P in surface water can result in about 500 lb of cyanobacteria (bluegreen algae) production in water.
Producers with high soil P should take serious steps to draw down soil P levels. They should try to avoid manure application on fields testing over 200 lb P/ac and not apply manure on fields testing over 400 lb P/ac. Efforts should be made to grow crops with high P requirements to draw down soil P levels. For example, growing crops such as alfalfa or cereal silage to draw down P soil levels would be a good management practice.
Developing best management practices
To prevent problems from developing, intensive livestock operators should adopt best management practices (BMP). When developing a long-term manure management plan, producers have to decide whether to apply manure based on N or P. In the long-term, it is advisable to use P as the nutrient to match with crop removal, rather than N.
It is important to remember BMP will vary from farm to farm, depending on the climatic zone of the farm, the type of animals in confinement, number of animals in confinement, total amount of manure produced, and how the manure is handled, stored and applied. It will also depend on the amount of land available to apply manure, soil types on the farm, types of crops grown and the yield potential of each crop. BMPs should be tailored to match the needs of each farm, and following a step-by-step approach is essential.
Determine where and how much manure can be applied
The factors of where to apply the manure and what rates to apply require the greatest attention. These two factors go hand-in-hand and involve identifying the fields where manure should not be applied, determining the acreage of each field and soil testing each field.
Soil sample each field to a depth of at least two feet and take depth samples at 0-6, 6-12 and 12-24 inches. Have samples analyzed at each depth for nitrate-nitrogen, phosphorus, potassium, sulphate-sulphur, pH and electrical conductivity (EC – a measure of salt in the soil). Take at least 20 random sampling sites across each field to make up a composite soil sample for each depth. Ideally, each field should be analyzed each year, either in late fall or early spring, to track soil nutrient changes and for manure and fertilizer planning.
This information is needed to identify which nutrients are excessive, high, adequate or deficient in each field. This allows you to determine how much of each nutrient must be added to the soil to ensure adequate nutrient levels for crop growth, and which nutrients are high or excessive in a field.
Representative manure samples should be taken and analyzed for total and available nutrients, specifically N, P, potassium (K) and sulphur (S). “Available” nutrient refers to an element that is in plant available form or one that can be rapidly released for uptake by growing plants in the year of application. “Total” nutrient refers to an element in both plant available and unavailable forms. When determining manure application rates, available nutrients and a portion of the unavailable nutrients that can be released from manure in the year of application must be matched to crop nutrient requirements in each field. Book values of typical nutrient levels in manure can be obtained from provincial agriculture departments.
Some operations may find they don’t have a sufficient land base for matching the total P in manure with crop removal. This may mean expansion of their land base or working with adjacent farms to apply manure. In addition, commercial N fertilizer may have to be added to make up the difference between what the crop requires and what is contained in the manure.
All information gathered can be put together to develop a manure management plan. Each provincial agriculture department has work sheets and computer based programs to help work though this exercise and specialists are available to assist with the planning process. Although it seems like a daunting exercise, it is essential in planning your manure management program and to optimize crop production.
DEVELOPING A MANURE MANAGEMENT PLAN
This is a simple case study outlining how development of BMP might work:
- Small feedlot in southern Alberta with 1600 acres (10 quarter sections) of irrigated land.
- Feedlot produces 10,800 tons of manure annually.
- All fields are soil tested and found to have between 50 and 80 lb of N/ac in the top 24 inches of soil.
- Two fields have soil P levels above 400 lb P/ac, three fields between 200 and 400 lb P/ac, five fields level 400 lb P/ac. Therefore, the two fields high in P should not receive manure.
- Manure was analyzed and found to have about 5 lb of N/ton and 15 lb of P2O5/ton that will be available to a crop in the year of application..
- If plant available N content of manure = 5 lb N/ton x 10,800 tons of manure, then 54,000 lb of plant available N is produced annually in the manure.
- If plant available P2O5 content of manure = 15 lb/ton x 10,800 tons of manure, then 162,000 lb of P2O5 is produced annually in the manure.
Manure management based on N:
If crop removal averages between 150 and 180 lb N/ac with various irrigated crops grown, and 50 to 80 lb of N comes from the soil, the remaining 100 lb N/ac would come from the manure. Thus, 54,000 lb of N from manure ÷ 100 lb of N/ac = 540 acres of land needed annually for matching manure application with crop removal.
Manure management based on P:
Assuming average irrigated crop removal is about 60 lb P2O5/ ac, then 162,000 lb of P2O5 in manure ÷ 60 lb of P2O5/ac = 2700 acres of land needed for matching manure application with crop removal.
In this very simplified example, a 540 acre land base would be needed for matching N in manure with crop removal, but would result in serious over-application of P to land in the long term. However, a 2700 acre land base would be needed for matching P2O5 in manure with crop removal. Keep in mind the farm has several fields with high soil P that should not be manured.
In this simple example, the farm has a land base of 1600 acres, minus 320 acres that should not be manured, leaving 1280 acres available for long-term sustainable manure management. The farm would require about 1420 additional acres for managing manure based on P.
In situations where intensive livestock producers do not have a large enough land base to balance manure application with crop removal of P, there is an opportunity to work with a neighbour. Indeed, the potential to purchase manure by paying for delivery and spreading has a double benefit. The confinement operator can dispose of extra manure, and the nearby neighbour has the advantage of an excellent source of fertilizer. In addition, manure applied to eroded fields will benefit from improved soil physical quality and productivity.
Oats can be a good rotational crop following alfalfa under irrigation. They can be grown relatively cheaply without nitrogen (N) fertilizer, have low seed costs and have very high yields. In years when oat prices are high, they can be a good choice.
“Our oat yields on first year alfalfa breaking were almost 250 bushels per acre under irrigation,” says Gary Kruger, irrigation agrologist with Saskatchewan Ministry of Agriculture at Outlook, Sask. “If a grower wants to take a holiday from high input costs, then oats can be a good option on alfalfa breaking.”
Kruger conducted a demonstration research trial in 2013 on one- and two-year alfalfa breaking to help determine the yield response of oat to different N fertilizer rates. The trial consisted of first year alfalfa breaking that was terminated in the spring with glyphosate, and second year alfalfa breaking with oats sown on canola stubble. The plots were sown with a no-till drill, and two oat varieties were planted: a milling variety, Triactor, and a forage variety, CDC Haymaker. The oats were fertilized at 0, 25, 50, 75, 100 and 125 kg of N per ha (kg/ha x 0.89 = lbs/ac). A split plot design was used, randomized and replicated four times.
The irrigated plots were at the Canada-Saskatchewan Irrigation Diversification Center at Outlook, Sask. The plots were seeded May 24, 2013. The forage plots were harvested August 20, 2013, and the milling variety was harvested for grain on September 19, 2013. The first year breaking plots were on non-saline areas, and the second year breaking plots were on a moderately saline site. Salinity was the reason for the lower oat yields on the second year breaking as compared to the first year breaking.
No N fertilizer required on first year breaking
There was no significant response to nitrogen application on the first year alfalfa breaking, indicating that farmers could successfully grow oats on alfalfa breaking without N fertilizer. The second year breaking showed a forage and grain yield response at 25 lbs N.
“Dryland farmers might doubt that you can grow alfalfa on first year alfalfa breaking without nitrogen, but with irrigation and warm soil temperatures, the soil is wet enough and the microbes active enough that you get good mineralization of N from the organic matter,” explains Kruger. “On dryland, you might not get that release unless you have very good early season rainfall that will replenish the soil moisture.”
Another advantage going for oats is that they are relatively low users of nitrogen. Research at Agriculture and Agri-Food Canada at Indian Head, Sask., found that even in an annual cropping system on dryland, oats rarely respond to more than 55 pounds of N on stubble.
“Oats seem to do well without a lot of nitrogen. We took out the alfalfa with a burndown and seeded without tillage, and still got enough mineralization for high yield. And even if you don’t get a high level of mineralization, oats are more forgiving because of their lower nitrogen requirements,” explains Kruger. (See Table 1.)
|Table 1. Oat N-fertility on first and second year of alfalfa breaking in 2013. Means followed by the same letter are not significantly different at P=0.05. Source: Nitrogen Rate for Irrigated Oats on Terminated Alfalfa. ICDC.
Kruger points out that there are other challenges to growing oats. With grain yields in the 250 bushels per acre range, there are a lot of bushels to deal with: hauling to the grain bins, having enough storage for those yields and in transport to markets. Additionally, market access may not always be close at hand.
Still, Kruger says that if growers want to diversify their rotations, oats could be a good crop to get into rotation, after one- or two-year alfalfa breaking.
“With irrigation, there are several crop options after alfalfa. I think oats is a good option if its price is favourable.”
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