Agronomy: Pay Attention to the Details

To make sure your crop is getting enough nutrients, use tissue testing to confirm.

When we think about providing nutrients to our crops, most times we think about the macronutrients we apply and what we remove from fields in the grain. When we are managing our soybeans throughout the season, however, we need to understand what the soybean plant actually needs—not only to produce the seed that we will harvest, but also to complete its lifecycle.

For example, 100 bushels of soybeans will remove in the seed 380# N, 84# P2O5 and 130# K20. The crop however will need in excess of 500# N, 110# P2O5, and 250# K20. That is just looking at some of the macronutrients. The crop also needs to have a balance of secondary nutrients (Ca, Mg, S) and micronutrients (B, Zn, Mn, Fe, Cu, Mo) as well. I recommend a tissue sampling protocol during the vegetative stage and then again at several stages of reproduction.

I try to use this information as a score card to track where I am and to help make management decisions. We get to see the final score when we harvest, but by keeping score throughout, we can set our beans up with a winning combination to help complete the season. Also, when tracking year to year, we start to see some trends unfold.

For example, most samples that I pull will come back short in zinc, manganese and boron at several different growth stages. Lately, we are seeing copper show up deficient as well in some situations. This is a trend we will continue to keep an eye on as we push our yield limits and see if it is a weather situation or if it is actually a trend. Copper, iron and manganese are all involved in photosynthesis as well as in protein production. Zinc and boron are important in plant vigor as well as in reproduction. These micronutrients are needed in small amounts by the plants and we have products that can be foliar applied to address these issues and help give our soybean plants an advantage.

It is important that we understand what both macro and micronutrients do for our plants so we can pay attention to any deficiencies and address them before they begin to take away yield. We want to first make sure our plants are never short on macronutrients. Nutrients have interactions with each other in our plants—we want to be conscious of this and strive to keep our nutrition in balance. Remember Justus von Liebig’s Law of the Minimum. It states that yield is proportional to the amount of the most limiting nutrient, whichever nutrient it may be.

When looking at tissue samples, generally we want to keep our plant tissue in the adequate range for the needed nutrient values. Once we have tissue samples to look at, we also need to ask ourselves what the results are telling us. For example, in the tissue we want to have about a 3 percent potassium level X, a 5 percent nitrogen level and 0.5 percent of phosphorus. Once we have the scorecard of a tissue analysis and we are deficient in any area we need to ask why. Is it because the nutrient is not available in soil? Are we having drought conditions or excess moisture that is slowing root development or nutrient uptake? Are we in a compacted area of the field? Some of the issues we uncover may not be able to be fixed this season. However, we may find some hidden hungers just by looking at the crop.

With the possibility of lower commodity prices on the horizon and a challenge in having profits at the farm gate we need to increase our level of management. This may not mean an increase in applications—by paying attention to the details we can realize greater returns. It does not help the bottom line to put all of our expenses into a crop, ignore that it is hungry in the reproductive stage and do nothing to address the problem. The way to stay ahead of the risk is to make educated decisions and realize the potential return that is in each of our plants.

Adam Day is a Certified Crop Advisor working with Northern Partners Cooperative in Ottawa, Illinois, as an Agronomy Account Manager. He works directly with growers on a daily basis, providing them with information and services to help them make decisions in their operations. His goal in working with farmers is to have a partnership to increase yield, profitability and sustainability.