The author is a water quality outreach specialist with the University of Wisconsin-Madison Division of Extension.
Climate change creates a multitude of issues for farmers, and it has two main components:
1. Increasing precipitation
2. Increasing temperature
Impacts vary by location and season. Changes, especially at the beginning of the growing season, present unique challenges to farmers and surface water quality.
Managing soil loss due to the spring thaw and rain is not new for farmers, but climate change will exacerbate issues created by the combination of cold winters and high amounts of precipitation experienced in parts of the country. This article will discuss the impacts of climate change in spring, the consequences of climate change with a focus on phosphorus, and practices to improve farm resilience in the face of rapidly changing weather in spring.
What is the new normal?
Using Wisconsin as an example, from 1979 to 2021, the state has seen a 2.6-inch uptick in the average March, April, and May precipitation (Figure 1). Spring is predicted to have the greatest increase in precipitation in this century (Figure 2). Extreme precipitation events (2 inches or more) are also on the rise. Spring is becoming wetter with rain falling in more extreme events.
Winter is warming the most of any season. This has an effect on spring through the change in snowmelt, by either reducing the total snowmelt or changing the timing of it. Winter thawing and subsequent refreezing is happening more often. In spring itself, average daily temperatures are projected to rise by 4°F to 5°F by mid-century.
Overall, springs are becoming warmer. This could mean longer growing seasons, but temperatures are more unpredictable, making planting annual crops riskier. Springs are also getting much wetter. The precipitation is more likely to come in the form of extreme events and be more erratic.
Less snow is falling in winter, reducing snowmelt volume in spring. The snowmelt is a source of soil moisture that is less likely to cause soil loss than intense storms. It is possible that spring droughts could be worsened by the absence of snowmelt.
Runoff and phosphorus loss
Fields that are bare or just planted are vulnerable to sediment and nutrient loss because those fields do not have the same capacity for infiltration that a mid-season crop field does. Consider a storm event of more than 5 inches of precipitation recorded by Discovery Farms in the month of May, which produced 1.2 inches of runoff, compared to a similar storm in August, which produced no runoff at all. Snowmelt and precipitation in March, April, and May saturate the soil, leaving it unable to hold more precipitation and causing runoff (Figure 3).
The majority of phosphorus in surface runoff from Wisconsin agricultural fields is lost from March to June. Particulate phosphorus is lost during the time of greatest soil loss in May and June because it is bound to soil particles.
Discovery Farms data consistently show large soil loss events in May and June due to heavy spring rains and soil disturbance. While 7,500 pounds of soil per acre was lost on a Rock County site, it carried with it 6.8 pounds per acre of particulate phosphorus. Practices to reduce soil loss will be best suited to also reduce particulate phosphorus loss.
Dissolved phosphorus is lost during the time of greatest total runoff, which is March. Runoff in March contains more dissolved phosphorus because it includes pore water, which has pulled phosphorus from the top inches of soil, snowmelt or rain on frozen ground that cannot infiltrate into the soil, or manure and fertilizer that has been surface applied on frozen ground. As winters warm and spring precipitation picks up, the peak runoff timing may change, along with the timing of dissolved phosphorus losses. Addressing the loss of dissolved and particulate phosphorus requires accounting for both meltwater and heavy spring rains, both of which will become more inconsistent in the future due to climate change.
Aim for resiliency
The key to building resilience is to utilize practices that improve infiltration and slow down runoff. Incorporating one or more of these techniques enhances overall resilience to unpredictable temperature and precipitation variances in spring and throughout the year.
Cover crops that survive and continue to grow through the winter address the challenge of increasingly wet springs by establishing biomass to improve soil health and water infiltration. Belowground biomass and aboveground cover can reduce runoff, soil loss, and phosphorus loss.
Improve nutrient application and manure management practices so rates and timing line up with crop needs to ensure fewer nutrients are left at risk for runoff.
Reduce soil disturbance and maintain crop residue to improve water infiltration. More water is drawn into the soil, lowering runoff during extreme rain events and before crop canopy is established. This also bumps up the amount of water the soil can hold before it is saturated, which helps sustain soil moisture during dry periods.
Consider planting flood-prone areas to permanent cover. You will gain a filter strip, a riparian buffer, and benefit pollinators all in one. Extreme storms make planting in wet areas more risky, leading to yield reductions and planting or harvesting delays that can impact profitability. This practice relieves that risk, improves resilience for the rest of the field(s), and can provide forage quality.
Explore agroforestry practices such as windbreaks and hedgerows, alley cropping, and silvopasture systems. These can slow down and filter runoff, keeping more nutrients and soil in place.
Spring is already a time of tremendous seasonal change. The shifting climate will push those changes to their extremes. Farm resilience to those extremes means planning for a broad range of events, from droughts to floods and early thaws to late freezes.
The pathway to resilience must also be broad and layered.
This article appeared in the May 2024 issue of Journal of Nutrient Management on pages 18-20. Not a subscriber? Click to get the print magazine.
