What is the difference between nutrient uptake and nutrient removal? How are they used to calculate nutrient harvest index?
Cristie Preston, Ph.D.
Agriculture has always been an integral part of Dr. Cristie Preston’s life. She grew up in southwest Virginia and had interest in crop and animal agriculture since an early age. Once she began college, she initially chose to study animal science but switched to soil science. Dr. Preston attributes her decision partly to an influential professor who told her, “You can’t understand animals until you understand what they eat.” She received a Bachelor of Science degree in animal science and a Master of Science degree in crop and soil environmental science from Virginia Tech. Dr. Preston holds a Ph.D. in agronomy, focusing on soil fertility from Kansas State University. While completing her advanced degrees, Dr. Preston conducted more than six years of field and lab research. Dr. Preston has experience in laboratory research measuring volatility loss from urea-based fertilizers. Her field research has focused on phosphorus availability and the interactions with tillage and placement. She also has extensive experience in working with large data sets and analysis. Her main priority is helping growers to identify yield-limiting factors and fix those issues as cost efficiently as possible.
When developing a nutrient management plan, there are two essential concepts to utilize: nutrient uptake and nutrient removal. Nutrient uptake is the amount of each nutrient required for the crop to complete its life cycle at a given yield level. Nutrient removal is calculated by taking the concentration of each nutrient in harvested material and multiplying by the harvest yield. Generally, uptake levels are higher than removal of nutrients in grain crops like corn (table below). However, in crops like alfalfa or silage where the majority of the above ground biomass is being removed from a field, removal levels can be approximately equivalent to uptake. These values are essential for determining nutrient application rates for current and future crops.
Nutrient harvest index is calculated by dividing the nutrient removed by the nutrient uptake then multiplied by 100 to get a percent. In this example, corn has a high phosphorus harvest index, which means that approximately 79 percent of the phosphorus that is taken up is removed in the grain. Harvest index is especially important when considering nutrient management decisions. Since a high portion of the phosphorus is translocated to the grain and removed, it is important to make sure yields are not phosphorus limited and adequate levels are supplied for subsequent crops.
Total macronutrient and micronutrient uptake and removal in Urbana, IL, and DeKalb, IL (2010), for corn averaging 230 bushels/acre. Harvest index was calculated as the ratio between nutrient removal with grain and total nutrient uptake and is reported as a percent.