Feeding our vegetable crops
We all need food to grow and prosper. Our doctors tell us that a balanced diet is one of the keys to a healthy life. So it should be no surprise that plants also need a nutritious diet! Natural plant systems like forests and prairies eat what Mother Nature provides by teaming up with a huge array of critters from bacteria to bugs to break down old detritus and soil into the essential components of their diet, like nitrate and carbon. Some have even evolved fantastic, mutually-beneficial arrangements with bacteria and fungi that allow them to pluck nitrogen from the air or move nutrients into the roots more efficiently!
This works well for natural systems, but when it comes to crops, where we demand maximum levels of productivity to supply the food needed to feed a growing population at prices they can afford, farmers must provide everything the plant needs themselves. The components are relatively simple with nitrogen, phosphorous and potassium (N, P and K) as the main food groups and a slew of micronutrients such as boron, copper, manganese and zinc that each crop needs in differing amounts. Determining what is needed by each crop, exactly when it is needed, and in what proportions is a lot more complicated. The consequences of not getting this right can be severe—for both the crop’s health and the farmer’s budget. Purchasing and applying the needed nutrients can be the largest input cost that a farmer faces. If you buy and apply too little, then it can reduce yield and quality. Too much can upset the plant’s well-being causing it to produce all leaves and little fruit and reduce yield. Or even worse, can result in serious environmental damage by leaching into groundwater or contaminating lakes and streams. The farmer’s goal is to know 1) what is needed, 2) how much is needed, and 3) when it is needed to supply the exact balance of nutrients for optimal plant growth, productivity, and quality. And famers need do all this in an ever-changing climate, with variations in weather patterns from year to year!
In the Central Sands of Wisconsin, where many of the nation’s vegetables are grown, farmers face the challenge of meeting the nutrient needs of an array of vegetable crops which include potatoes, carrots, green beans, sweet corn, peas, beets, cucumbers to name a few, as well as grains such as corn, soybean and oats. Each of these crops has specific fertility requirements, and growers need to know the optimal fertility programs of all of them to achieve the needed levels of productivity.
It all starts with knowing what is already in the soil, and this process begins the fall before planting when hired crop scouts crisscross fields slated for vegetables to take soil cores for sampling purposes. These soil cores are sent to certified labs where detailed analysis determines what levels of nutrients are already in the soil. With this information in hand, farmers use University of Wisconsin fertility recommendations—developed over decades using complex research and development programs— to carefully match what additional nutrients are needed. Although complicated and expensive, it is an essential step in being both economically sustainable and environmentally responsible. Each nutrient is calculated separately, and while there is an ideal amount for each crop, farmers adjust that level downward based on what the soil can provide. For example, the amount of nitrogen needed by a crop can be reduced by many factors in their operations, such as soil organic matter, manure application or previous crops which can leave nutrients in the soil for the next crop to use. Some crops, like alfalfa, can actually fix nitrogen from the air—farmers can take advantage of these complex systems to farm as an integrated ecological system, not just as individual crops.
Next, farmers determine the best timing of application to optimize plant use of these nutrients. Many times, the plant is spoon-fed the remainder of the needed nutrients by providing the crops with small amounts at optimal timings and plant growth criteria throughout the growing season. This process is often refined by analyzing tissue samples as the crop matures to be sure that plants have enough nutrients to thrive. The system works well, achieving high productivity with the greatest efficiency possible, but farmers and researchers from the UW Soil Science Department are committed to improving it further. On-farm research has already been established to improve the precision of applications using Global Positioning Systems (GPS) technology to apply variable rates that match changing soil types across fields. Other research is looking at providing on-demand delivery of the nutrients using drip irrigation systems which puts the nutrients right at the root zone.
University of Wisconsin Soil Science Specialist, Dr. Matt Ruark, is working with Central Sands growers by conducting extensive trials aimed at improving nitrogen-use efficiency by crops and reducing the potential for environmental impacts with slow-release fertilizers. These types of fertilizers can hold leachable nitrogen in the soil during periods of heavy rain. As Matt says, “nitrogen is a major cost to farmers and the potential to impact water quality is always a threat. Our research will reduce that threat and help vegetable farmers to be more sustainable.” The vegetable farmers of the Central Sands are recognized leaders in developing and using innovations that provide a secure and affordable food supply to the nation while protecting the area’s natural resources. Feeding the crops only the nutrition they need is complicated and can be expensive, but the investment is more than justified, resulting in a sustainable food supply system.