Postharvest sampling

As growers of the nation's, and the world's, food supply, finishing the growing season well is important. You’ve worked hard all year to set, grow and harvest a crop of both high quality and profitability in a tough year and market. As this growing season is coming to an end, one thing you don’t want to forget is to complete your post-harvest treatment plan, which should include both soil and plant tissue sampling. This is typically performed prior to harvest time, but for early maturing crops, this would be anytime after late-July through mid-August depending on your growing area. It’s also important to have a working understanding of why this is important. 

Let's start with soil sampling and an introduction from the 10,000 foot level - getting your soil to perform better and be more productive is critical. Oftentimes this can be treated with a shortcut approach or fast tracked by someone whose focus is to make a sale. In truth, correcting soil issues is an involved process that can be quite complex, and rarely will a "silver-bullet" approach be effective. This is why very few will address it completely to the finish, because it takes time and resources to change the soil composition (in the top 6 inches for row crops or 12 inches for permanent crops.) With row crops, in that top 6 inches of soil, we're talking about right around 2 million pounds of soil per acre. And with permanent crops at a 12 inch depth, it's double that at 4 million pounds per acre. Sampling the appropriate depth provides a good representation of the nutrient inventory and its potential availability for the crop to be grown. It also represents the area where the majority of the root zone activity happens. I mention the majority of the root zone because there are a lot of factors that affect root zone productivity in terms of nutrient availability for plant and crop benefit.

In general, the three main factors contributing to healthy soil are, physical, chemical and biological properties. When these are in proper balance, soil health is the result.

Physical properties include the sand, silt and clay content of the soil in terms of percentages or proportions; it is also referred to as texture. It's what you've got to work with and is often referred to in terms like ‘sandy loam’, ‘silty clay’ or ‘clay loam’. Based upon the texture of your soil, you can also make some reasonable inferences - like its ability to hold nutrients, its soil-water characteristics or its tendencies towards compaction.

The chemical properties, are anything added to the soil – such as, fertilizers (including dry or liquid, inorganic or organic forms), or amendments - like gypsum, limestone or sulfur. Water should also be taken into account, consider that rainfall, surface water, or groundwater each have different effects on your soil's chemistry. Finally, you must be thinking about any of the ‘-icides’ – like herbicides, fungicides, insecticides, nematicides, etc. These are all different chemistries that each affect the chemical composition (and biology) of the soil.

This brings us to the biological properties. This is the life in the soil, including micro- through macro-organisms. Microorganisms like bacteria, fungi, yeast, algae, nematodes, etc. Macroorganisms would include slugs, snails, earthworms, beetles, centipedes, gophers etcetera. 

This is a condensed list, but I think it demonstrates well that there are a lot of moving parts involved in building and maintaining the health of the soil and that nothing happens in a vacuum. A misapplication affects all of the factors and create limitations to the soil’s ability to be productive. Soil sampling is a useful way to reduce, if not eliminate, the chance of this happening.

When it comes to post-harvest sampling, one question I am often asked by growers is, “Should we collect samples from the strong (healthy) or weak (unhealthy) areas of the field?” Every farm is as unique as the individual blocks within it, so, in many scenarios this is a case by case situation decision and you should make it with the guidance of your Crop Adviser. In terms of precision-minded planning, it’s critical that we don’t shotgun every decision. Sometimes we have to be more precise, and that's a good thing, but it's also important to be sure that your efforts to be more precise will be worthwhile. Here's why, in the large majority of instances like this, I have seen very little, if any, significant difference in terms of nutrient inventory when comparing results of healthy versus unhealthy parts of a block. Which means that, in most cases, it isn't so much a circumstance of healthy versus unhealthy, but rather weak versus weaker or unhealthy versus unhealthier parts of these blocks. This is based on countless samples analyzed and grower conversations I've had over the years about their fields. Remember, blocks are typically fertilized the same way, which eliminates fertilizer inputs as a variable. As long as adequate fertilizer was applied, plants were fed, which leaves the physical and biological portions of the soil, and in most cases when there is an issue of canopy chlorosis or uneven growth, for example, the soil texture or physics or physical nature of the soil is pretty similar as well. This leaves the biological portion of the soil to be addressed. 

So where should we start? You might need a soil sample as well as a soil microbial respiration rate test to measure your biological populations and activities. This is something that not all Ag labs offer, so proceed carefully and with good counsel with your lab selection. A good representative sample pod for soil analysis should be adequate, but if you feel strongly about comparing, talk with your crop adviser about arranging the details. Be sure to keep track of them and the treatment progress by maintaining a year after year data archive. This is something that our SoilMatters growers have come to not only appreciate, but count on. Otherwise, what would be the point of going to the extra effort and expense if you aren't going to monitor and follow up? So, based on all that, I have found that in most cases, these extra efforts, in terms of sample sites, aren’t always necessary. 

The important take-away is that, as we move into or through harvest, it's time to begin planning for next season. This should include the appropriate sampling, and that might include microbial respiration rate testing too. Don’t let this seem like a daunting project. If you’d like some help improving or maintaining the health of your soil, we’re here to help! Contact us directly through the button below. 

Here’s to your crops’ success!