Is less more? Understanding the Law of Minimum to optimize your fertilizer strategy

Identify and correct crop nutrient deficiencies in your soil to increase yield and profit

Achieving prosperity in Canadian agriculture is a balancing act. While new technologies increasingly grow your potential to overcome limiting factors and boost yields, oftentimes revisiting the basics will further support your efforts to reach an optimum balance in soil nutrients. A great place to start is Liebig’s Law of Minimum.

This law is all about removing limitations within soil health. But, if you cut back on fertilizer rates, will your yields – and profits – decrease? Will more fertilizer boost yield? The answer to both questions is, not necessarily. When it comes to soil fertility, properly applying the Law of Minimum can bring clarity to decision making and ease the impact of adverse weather, disease and pests, all while maximizing economic yield.

You might think it’s been a while since you’ve factored this law into your fertilizer strategy. But you’re likely using it without even thinking about it. Let’s dig in and rediscover this concept. Especially, how you can put it to work for optimal nutrient uptake across your crops, thus achieving the most profitable yield possible.

Agronomy 101: Remove limiting factors using Liebig’s Law of Minimum

Put simply, this law states that plant yield depends on the performance of the least available nutrient. So, a plant’s growth rate, size and quality all depend on the available amount of the most limited nutrient in your soil. Therefore, yield is more appropriately determined according to the soil’s most deficient resource, rather than the abundance of total nutrients available. In many cases excessive nutrient levels will prevent nutrient uptake within other sources.

Abiding by this law is a delicate balance. You’re working to ensure no nutrient is deficient and that’s no easy feat without the aid of comprehensive soil testing and an informed variable rate prescription.

To understand how this all plays out in your soil health, the Law of Minimum is commonly demonstrated using the analogy of a barrel of water with staves of varying lengths, each representing a particular nutrient. This barrel can only hold water up to its shortest stave. Now, if the longest stave, let’s say nitrogen, is six feet tall, while the shortest, perhaps calcium, measures only three feet, that three feet of calcium is the “limiting factor.” It is where all the water (or total nutrients in this case) will run out. Furthermore, in building the tallest stave, you’ve decreased your resources, or investment, to build up the other staves and achieve an effective balance.

Seems simple. But surprisingly, the Law of Minimum is often overlooked when it comes to fertilizer strategy in the pursuit of simultaneously overcoming limiting issues and boosting yields. This is where working closely with your agronomy professional to identify and remove fertility issues that limit your yield becomes the difference maker to protecting your nutrient management investment and ensuring a prosperous, high-yielding harvest.

The Law of Minimum in action

Addressing limiting growth factors requires a deep-rooted understanding of what’s happening in your soil. To gain that insight, both technical expertise and detailed observation of plant performance in response to fertility applications are essential.

Suppose you work from a guessing standpoint rather than an informed one. “If you’re working towards a high yield goal and you plan to apply tons of nitrogen but only place a minimal rate of phosphorous for that crop, that overapplication is actually causing a deficiency,” said Garth Donald, Manager of Agronomy and Founder at Decisive Farming by TELUS Agriculture. “The Law of Minimum now comes into play. Your yield factor is based on that deficiency. It’s not based on your nitrogen – that feel-good instant application – over the phosphorous which doesn’t necessarily give that feel-good instant response.”

In this case, you now face the danger of limiting yield and losing profit. You can realize better yields and avoid detrimental nutrient interactions if you identify exactly where yield-limiting factors should be removed. To truly know where fertility dollars should be allocated, accurate soil testing is your best asset. If you’re relying on visual, above ground signs in the plant, it might be too late to save those extra bushels.

“If you underapply phosphorous or sulphur and overapply nitrogen, you will have a negative effect on yield,” said Donald. “The first thing you’ll see in both cases is purpling, a sign of deficiency. But that can also be caused by other nutrient deficiencies or chemical injuries.”

Later in the season, Donald warned, nutrient unbalance such as phosphorous deficiency and excess nitrogen will cause sluggish growth and lower the fruit sets in the canola flower if not applied in sufficient amounts where and when needed. By the time you notice cupping in the leaves, discoloured flowers in your canola or poor seed set in your wheat, it may be too late to rescue those extra bushels you aimed for.

Meet your 4Rs using the Law of Minimum

The Law of Minimum clearly addresses the “right rate” and “right source” components in 4R Nutrient Stewardship. It also meets the right time and place factors when technology is an extension of your crop management plans. By combining this law with comprehensive soil testing, crop monitoring and a strong variable rate program, you’ll invest your fertility dollars in the most efficient way with the right amount of each nutrient applied only where each is needed and at the precise time it will have the most impact.

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