Management practices are crucial in determining forage production and quality in forage systems. Among them, fertilization is essential to supply nutrients needed by plants. Over the past decades, the fluctuation of costs of fertilizers has elevated the importance of improving nutrient use efficiency while also seeking alternative strategies to reduce off-farm inputs into forage systems. Understanding the main points for improving nutrient use efficiency and distribution in forage systems can help improve feasibility and sustainability in forage systems.
Soil testing is a crucial management tool to monitor soil fertility and pH and allows for proper nutrient amounts to be applied as needed by forage crops. Routine soil testing can help save money on lime and fertilizer applications while decreasing nutrient losses and runoff. Soil testing should be conducted at least every two years and, in order to have reliable information to develop your fertilization program, soil samples must be collected correctly. The general recommendation is to collect 15 to 20 samples to 6 inches depth in a field up to 10 acres. Samples should be collected in a zigue-zague pattern throughout the area and placed in a bucket, then homogenized prior to sending up to a pint to the lab for analysis.
Besides providing proper nutrient recommendations, routine soil testing allows for the maintenance of adequate soil pH. Improper soil pH will impact nutrient availability and root development affecting overall forage stand establishment, production, and persistence. Lime is frequently used to increase soil pH and may be required to be applied 6-8 months ahead of the establishment of a new forage stand, depending on the current soil pH. Typically, by raising the soil pH, nutrients, as N and P, increase their availability. However, the target soil pH varies with the forage crop being used, and, in general, legumes have higher nutrient and pH requirements than warm-season grasses, for example.
Once you have your soil report recommendations in hand, make sure to choose the fertilizer source that best fits your needs so you do not apply unnecessary nutrients. Commercial fertilizer blends that supply N, P, K, and micronutrients have specific combinations and can be a source to apply more than needed nutrients for your area, which represents increased costs. For example, if your soil test report shows that no P is needed, then you should select a fertilizer blend that has no P. Your local Extension agent can help you choose the appropriate fertilizer source to use based on your needs.
Overall, the use of organic fertilizer sources (ex. animal manure, chicken litter) has been increasing over the last decades due to attractive costs and high local availability. When using organic amendments, in order to properly meet forage crops’ needs, it is important to know the fertilizer composition and understand the rate at which the nutrient (s) is released. Some organic fertilizers may also be a source to increase organic matter in the soil over time which is particularly important to improve soil fertility and resilience.
For any source of fertilizer, the nutrient composition of that source, time, and rate of application will impact the effectiveness of its use and have environmental implications. Generally, when we are developing our fertilization plan for a given forage, the determination of how much fertilizer needs to be applied will depend on the nutrient levels available in the soil and the expected forage production during that growing season. For N fertilizer, it is recommended to split apply the total rate over the growing season aiming to optimize the absorption by plants and reduce runoff and leaching to water bodies.
Management practices and the choice of species will also have an important role in the nutrient input required. Improved forages, such as bermudagrass and legumes, may have higher fertilizer needs than bahiagrass, for example. However, it is important to properly address their needs based on the management that is applied. Intensity and frequency of grazing or cutting for hay production may require different levels of nutrients to be replenished based on the amount being exported. Under grazing, rotational management can be an alley to help with nutrient distribution throughout a pasture once animals stay for limited periods of time in a given area and avoid creating areas where animal excreta are accumulated which often happens on shaded and waterer areas on pastures under continuous stocking.
Thus, the incorporation of legumes into forage systems can help with inputting N through biological fixation and increase soil fertility. Legumes are only able to fix N in association with specific bacteria, which requires the seeds to be inoculated. Then, N fixation ranges from 40 to 100 lb N/acre but, it will depend on the forage yield. The organic N fixed can be available for companion grasses in mixtures or to the subsequent grass crop. The use of legumes in forages systems has been increasing, aiming for improved forage production, nutrient cycling, and animal performance, especially in low-input systems where there is little to no replenishment of nutrients routinely.
Submitted by Liliane Silva, Ph.D., Assistant Professor and Extension Specialist,
Forage-Livestock Systems, Department of Animal and Veterinary Sciences, Clemson University
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