The 4Rs: Getting Crop Fertility Right

Explore why right time is a critical component of 4R nutrient management when it comes to optimizing crop fertility

January 11, 2024
4 mins
Dr. AJ Foster
Agronomy Technical Services Manager, Southern US

What are the 4Rs? 

To reach a destination, you have to know where you are going and the steps along the way to get there. 

The goal in crop management is to produce the best crop through smart planning and execution. To do this, many factors must be addressed. For ultimate crop productivity, every grower should aspire to achieve the 4Rs as they consider fertilizers: 

  • Right source at the 
  • Right rate at the 
  • Right time and in the 
  • Right place 

The 4Rs were established as guideposts to help us manage and protect natural resources and improve sustainability, while also deriving the best value from any fertilizer product that is used. 

Why is setting the right goal important for grower profitability? 

The beauty of agriculture is that no year ever repeats itself. (Of note, that may also be one of the most frustrating things, because that means there’s no “easy button”!) Not only is each year different, fertility is also crop-specific, region-specific and grower-specific. With all those variables, the 4Rs provide the foundational questions growers should focus on annually.  

The right fertilizer source, right rate, right time and right place are all determined by the ultimate goal. When these are in sync, the fertilizer is taken up by the plant and nurtures the final product. So, for me, the goal is not to produce the biggest yield possible; it is to sustainably optimize grower profitability. Farming sustainably also improves profitability by protecting soil and water, a farm’s most valuable assets. 

If you can’t measure something, you can’t manage it. The 4Rs lead you to look at what you should be measuring and by doing that, you can start evaluating performance. Assessing the 4Rs post-harvest allows us to evaluate the success of the fertility management program. Was the right fertilizer applied at the right place? Was the rate right, and did the timing work well? And as the new season comes into clearer focus, what should be changed next year?  

 It starts by making sure that every unit of fertilizer applied is bringing real value in terms of the final products that are produced. Then you can achieve the best efficiency for whatever unit you’re applying, because it is not lost in the environment and is actually doing what it’s intended to do – produce the best crop. 

Why is Right Time such an important component of 4R nutrient management?

Of the 4Rs, the difference between success and failure is usually not determined by the right place or even the right source. The right time is often the most critical aspect and the most difficult to achieve. 

There are approximately 150 days from when a seed is put in the ground to when the crop is harvested. Each crop has its own window when it is best for fertilizer to be applied. For some crops, that window may be a wide-open door – or it might be just a keyhole in which you have a very small opportunity to get it right. If you miss that window, you can’t go back because the crop keeps growing.  

The weather is always an unknown factor in farming, so growers need to look for solutions that work regardless of the weather. Most fertilizers, especially nitrogen and sulfur, are susceptible to leaching, which makes timing even more critical. Fortunately, there are some technologies available that can help mitigate this reality. Controlled-release fertilizer provides a nutrient source that’s consumed continuously, providing the crop with fertilizer throughout the growing season. Products with sustained release, like ICL’s Polysulphate® (natural mineral polyhalite), can relieve some of the pressure because it can be applied early and have sustained release for a longer period.  

Applying at the right time is closely connected to choosing the right source. For example, there are many different sources of sulfur, and they each have different release patterns. It’s important to have a good understanding of how different fertilizers release nutrients and how that matches with the crop within your specific environment. When using ammonium sulfate, the sulfur breaks down quickly and a heavy rainfall could cause most of the nutrients to be lost. Polysulphate® only releases a small amount of nutrients at a time, so a large rain event would only affect a small portion, leaving the sulfur available to release throughout the rest of the season. 

The 4Rs – right source, right rate, right place, right time – allow a grower to look both forward and backward. These guidelines can evaluate the past year’s performance and plan for the next because these questions need to be asked and answered every year. 

It’s important to start with the right questions to get the answers you need. The 4Rs are the right questions to achieve the goal of optimizing grower profitability.