Nutrients come from a variety of mineral or synthetic fertilizer sources, and many producers also rely on organic materials including manure and compost. Application methods and equipment depend on the crop, fertilizer source and application timing. Common methods include broadcast, injection and banding.
Responsible use of fertilizer is not only a sound environmental practice, it is also a profitable one. To that end, the 4R nutrient stewardship principles – right source, right rate, right time, right place – help producers and agronomists make sound management decisions regarding nutrient application. In this article, we will briefly examine the principles and how you can carry them out on your operation.
Right source
The first 4R principle, right source, addresses the type of nutrients you choose to apply to a given crop. Matching what you apply to what the crop actually needs helps promote strong, healthy growth while minimizing financial waste and losses to the environment. Work with your local agronomist or university extension agent to scout and pull soil samples to determine what the crop needs most.
The nutrient source to fit those crop needs may come in a variety of forms. Synthetic or mineral fertilizers typically come in granular, liquid or gaseous forms depending on the primary nutrient. Though they can carry a significant cost, one advantage of these fertilizers is: They are fairly consistent and commonly labeled with the nutrient content, making it easy to track what you actually apply to your fields.
Many livestock producers utilize manure as a primary source of nutrients for their forage crops. In addition to minimal or no material costs, using what comes out of the animals to grow what goes back into the animals is a great form of nutrient recycling. Depending on the livestock it came from and other management practices, manure may contain high levels of liquid or take the form of pen pack or separated solids.
No matter the type of material, manure can contain varying levels of key nutrients. Regular analysis will help you understand what is in your manure so you can adjust the application accordingly. In many cases, a combination of manure and granular fertilizers might be the best solution. Manure can be very rich in nutrients such as phosphorus, which may limit how much can be applied without risk of leaching or runoff. As part of an overall nutrient management plan, a granular fertilizer could also be applied to augment the nutrients in the manure and help meet the crop’s additional needs.
Right rate
The second 4R principle, right rate, deals with how much of a particular nutrient you apply to your crops. Apply too little and the plants will not perform well, reducing your revenue; apply too much and you risk the excess nutrients finding their way into the environment while the excess cost hinders your profitability.
Applying whatever source of nutrients you choose at the right rate is all about your application equipment. Precision variable-rate capability and automatic GPS-controlled prescription maps keep you from applying too little or too much at a given spot in the field. Many sprayers, fertilizer applicators and manure spreaders offer rate-control systems and software integrated from the factory, or you can sometimes add these components to existing machines.
Coupled with weigh cells or other innovative sensor systems, the software adjusts the machine’s application according to the prescription map. When shopping for nutrient application machines, look for ones that offer high precision for the best return on your investment.
Right time
The third 4R principle, right time, focuses on when the nutrients are applied to the field. Applying nutrients as close as possible to the exact time the plants need them maximizes return on investment while minimizing loss to the environment. For forage growers harvesting multiple crops per year, applying nutrients between cuttings is a convenient way to replenish the nutrients removed from the field through the harvest process. Plant root structures are still in place to absorb the nutrients as they move into the soil profile. Be sure you apply soon enough after a cutting to jump-start regrowth.
Application outside the growing season can help prepare the soil for the next planting without risking damage to plants. This is especially true for soil amendments such as lime, which need time to adjust the soil’s chemistry and may not be practical to apply in-season. However, take special care when spreading fertilizer or manure outside of the season, especially in winter. Spreading on top of frozen or snow-covered soil greatly increases the risk of runoff. Not only does runoff wash away your investment, the excess nutrients can enter the water supply and contribute to issues such as algae blooms and high nitrate levels.
Right place
The fourth and final 4R principle, right place, emphasizes correct placement of nutrients to optimize return on investment while minimizing environmental impact. Placing the nutrients where the crop can reach them, while also keeping them out of waterways or non-crop growing areas, is critical.
Correct placement of nutrients also depends greatly on the equipment used for application and the nature of the material applied. Liquid and gaseous fertilizer or manure is typically injected into the soil and especially common in row-crop forages such as corn silage. While this allows the most control over the application, it often requires more power, fuel and time, and may not be conducive to feeding grass or legume forage crops between cuttings.
In many forage applications, broadcast spreaders are used with granular fertilizer and drier manure forms such as pen pack or separated solids. Broadcast spreading is relatively quick and efficient, but more care must be taken to keep the nutrients in the field. Fortunately, broadcast spreaders continue to improve with technology such as variable rate, and even section and border control, offering impressively high levels of precision.
Conclusion
No matter which forage crops you grow, feeding the growing plants properly will help you build an efficient, profitable, and environmentally sustainable operation. The 4R principles of right source, right rate, right time and right place offer an excellent framework to build your nutrient stewardship practices. 
Philip Loduha is a product specialist with Kuhn North America
