How nutrient loss is hurting your profitability — and what to do about it

Fertilizer is often one of the most expensive input costs in any farming operation. The bill you pay for fertilizer could account for a quarter (or more) of your total inputs. But those costs are especially painful when you lose some of those nutrients before your crop can even use them. 

Unfortunately, the Mid-South is particularly prone to nutrient loss. If you’re farming in this region, it’s time to think about how you keep those nutrients on your land — and profitability in your pocket.

What causes on-farm nutrient loss in the Mid-South? 

Runoff: In areas with poor drainage, nutrients can wash away during periods of rainfall. For example, between 0.2 and 5% of nitrogen and phosphorus on farms is lost in runoff each year, much of which ends up in the Mississippi and Gulf of Mexico. This runoff is direct profit down the drain.

Denitrification: During this process, nitrate in the soil gets converted by microbes into nitrogen gasses, which are then lost to the atmosphere. This means the amount of nitrogen actually available to the crop evaporates into the air.

In prolonged saturated conditions, farmers could experience between 2 and 5% nitrate loss per day, depending on soil temperature. Conditions directly following rainfall can lead to more nitrate getting converted to gasses — and decreasing the amount available in the soil. Say, for instance, you applied 240 lb/acre of nitrogen just before heavy spring rainfall. If your soil stays saturated for two weeks after that rain, you’ll likely end up losing up to 70 lb/acre of nitrogen to the atmosphere. Needless to say, this natural process can significantly hurt profitability.

Management practices: Historic tillage has caused an average organic matter loss of 30% from levels prior to the start of cultivation. Assuming that each 1% organic matter provides 20-30 pounds of nitrogen per year, the estimated organic matter lost from soils in the Delta would have provided an additional 20 to 60 pounds/acre of nitrogen each year. 

Organic matter is also an important source of phosphorus, sulfur, and other critical micronutrients. For example, there’s an average 100 pounds of phosphorus per 1% organic matter per acre. When this organic matter is lost, and you have to supplement with chemical phosphorus fertilizer, this costs about $70 per acre. 

How do you know if your operation is at risk for nutrient loss? 

When it comes to nutrient runoff, you’re at more risk for this type of nutrient loss if your land has steep slopes; however, significant runoff can occur on relatively flat fields with poor drainage or after heavy rainfall events. 

A bigger concern on flat land is nitrogen loss through denitrification. In flat fields, water is more likely to pond, especially if these fields have heavy-texture soil or compacted layers. This creates the prolonged saturation that promotes denitrification. 

Compacted soils are also more prone to runoff and denitrification losses. If your fields have had heavy equipment traffic and the soil has those compacted layers, this can be a risk factor for nutrient loss.

Also keep an eye out for consistent ponding in the spring and/or yellow, anemic-looking crops in those areas of ponding, as this could be a sign that the soil has experienced nutrient loss there. Ponding can also interfere with root development, which makes nutrient uptake more difficult for a plant.

NDVI imagery can help you spot these differences. However, low NDVI can also be caused by other stresses besides denitrification, so it’s best to follow up with a field visit and tissue sampling to confirm nitrogen deficiency. 

For those who have seen ponding on their farm, get targeted soil and tissue tests in that area, and compare results with healthier looking areas in the same field. This can be a good way to identify areas of nutrient loss from denitrification. 

How farmers can limit nutrient loss and improve overall soil health

Improve drainage: The better drainage you have on your fields, the less pooling you’ll have on the surface — and the more you’re helping water get into the soil instead of just hanging out above it. With better drainage, you’ll also reduce the risk of nutrients washing away if and when it rains. 

Focus on soil health: Year-round cover crops help mitigate soil erosion and increase available nutrients in the soil. They also help stimulate buildup of organic matter in the soil. The more you can restore the soil’s capacity to provide nutrients on its own, the less you’ll have to compensate with higher fertilizer applications. In the end, this means lower input costs and better profitability. 

Remember the four Rs of nutrient management: When you do use fertilizer, aim to apply the right rate, from the right source, in the right place, at the right time. Split your fertilizer applications and optimize your timing so that you put down nitrogen at the same time as the plant needs it. This helps you avoid a situation where the nitrogen is just sitting there on the soil — and is vulnerable to runoff or denitrification. 

Consider nitrification inhibitors: When fertilizer that contains ammonium or urea is applied to the soil, these are quickly converted into nitrate by microbes. In flooded conditions, this nitrate is particularly vulnerable to denitrification loss. Nitrification inhibitors can help prevent spring buildup of nitrate in the soil and delay the conversion of ammonium into nitrate—thus decreasing the window of time where your fertilizer is vulnerable to denitrification loss. If you’re in a high-risk field, these might be a smart option. 

Protect your soil health with customized regenerative recommendations

At Vayda, we’ve been putting soil health strategies like cover cropping, reduced tillage, and precision application into practice on more than 5,000 acres in the Delta. We combine the lessons learned from boots-on-the-ground work with soil science expertise to give farmers tailored recommendations to improve their farm’s soil health. If you’re curious how regenerative ag practices can protect your operation from nutrient loss, connect with one of our local advisors for a consultation.