Utilizing nutrients from the right rate can have a major impact on cost of inputs as well as the yields achieved for a given field and cropping season. The over- or under-application of nutrients can have a significant impact to crop production, expenses, and/or environmental concerns.
During times when fertilizers may be, for the most part, inexpensive in comparison to the value of the crop being produced, it may seem like the benefits of using a precise nutrient recommendation are relatively low. However, excessive nutrient application can lead to unintended outcomes such as lodging in small grains and rank cotton. Environmental concerns may also arise due to over-application such as P contamination in surface water bodies or N runoff into rivers and streams.
As the costs of nutrients increase and/or crop prices decrease, growers tend to gain more interest in soil sampling and determining a plan for the efficient and precise application of nutrients. By doing so, growers will see a greater utilization of the nutrients applied as well as their dollars spent on fertilizers.
Liebig’s Law of the Minimum is very practical when implementing the application of nutrients at the right rate. Liebig’s Law states that the crop’s yield will be determined by the element present in the most limiting quantity. Overall, one nutrient’s deficiency cannot be overcome by over-applying another. Because of this law, all 17 of the essential elements for plant growth must be present in the quantities required for optimal crop growth.
Each of the 4Rs depend upon the other three. In the case of right rate, it is conditional on the other “rights” of source, time, and place. The source of the nutrient needs to be released in the right amount of plant available forms at the right time during the plant’s growth cycle. The nutrient also needs to be applied in the right place to meet the needs of the growing plants.
There are six scientific principles supporting using nutrients at the right rate:
Assess plant nutrient demand
The best indicator of yield is to determine the quantity of nutrients taken up by the crop through maturity. It is important to set a reasonable crop yield goal that is attainable with optimal crop and nutrient management while taking into account variability within fields and the cropping season. Taking the time to determine yield goals and variability will help nutrient service providers and/or ag retailers provide important and accurate guidance for nutrient needs.
For information about total nutrient uptake by specific crops, visit http://www.ipni.net/ipniweb/portal.nsf/0/CBDC9962624CDFCD85257AC60050BBD2/$FILE/NAm%204_1%20%26%204_5%200115.pdf
Use adequate methods to assess soil nutrient supply
Most of the nutrients necessary for plant growth can be provided by soil organic matter. Many of the nutrients contained in soil organic matter are in very small quantities in regard to being a dominant source of nutrition, specifically with N and S. It can be difficult to predict the amounts of nutrients provided by organic matter to be in plant-available forms during the growing season due to mineralization and microbial decomposition.
What is the best tool for determining soil contributions for plant nutrient supply? Take a soil test. Soil sampling and testing serves as an effective tool for determining the right rate of fertilizer.
Assess all available nutrient sources
Although traditional fertilizer is commonly thought of as meeting crop nutrient needs, it is important to consider all sources of nutrients when determining the right rate of fertilizer. Some sources of nutrients outside of applied fertilizer include crop residues, green manures, animal manures, composts, biosolids, atmospheric deposits, and irrigation water. These sources can be difficult to determine in quantity and plant availability, but producers can utilize their ag retailer/nutrient service provider to build a nutrient recommendation plan with these factors taken into consideration.
Predict fertilizer use efficiency
Unfortunately, fertilizer utilized by the crop will never be 100% regardless of how many 4R and conservation practices a producer puts into place for their specific farming operation. However, producers can strive to minimize losses and increase fertilizer efficiency. Adjustments for efficiency need to be included in the discussion between producers and their ag retailer/nutrient service provider to determine accurate fertilizer rate requirements. Implementing 4R Nutrient Stewardship practices incorporating right source, time, and place in a well-managed cropping system will assist in producing high fertilizer use efficiency for determining the right rate.
Consider soil resource impacts
Soil is a vital resource in crop production and producers strive to maintain the quality of this resource. Soil can be impacted by plant nutrition in two main ways:
- By providing nutrients at levels optimizing plant growth, the plants return the favor by leaving an increased amount of organic carbon in the soil. This increase in carbon assists in the maintenance of organic matter in the soil.
- Many nutrients, such as P and K, are retained in the soil. Their addition to the soil can influence the levels of plant availability of these nutrients in the future.
Consider rate-specific economics
Producers can greatly benefit from building soil fertility levels to optimum range for the crops they grow. Increasing soil fertility can lead to greater flexibility in choices for source, rate, time, and placement of nutrients. By increasing flexibility, producers can take advantages of market conditions and price changes in fertilizer. Regardless of these factors, the economics of fertilizer application can impact the producer’s bottom line most by selecting the right rate of fertilizer to apply.
4R Plant Nutrition – A Manual for Improving the Management of Plant Nutrition (North American Version). International Plant Nutrition Institute. 2016.