Lessons (Ghosts) of Droughts Past

From Alberta to Iowa, the region has experienced everything from abnormally dry soil conditions to exceptional drought. In some places, the drought started in 2020 and has continued through 2021. Considering lower than expected crop yields, we expect that residual soil nitrate-nitrogen levels will be much higher than normal in many wheat, canola, and corn fields this fall. There was reduced crop nitrogen uptake and little to no soil nitrogen losses to leaching or denitrification through the growing season, which should result in higher soil test nitrate-N remaining in the soil profile.

In major drought years, high residual nitrate levels are a normal phenomenon. In 1988, the average soil nitrate test following wheat across the region was a staggering 107 lb/acre nitrate-N (0-24 inch soil profile). This is considerably higher than the long-term average around 30-45 lb/acre nitrate-N (0-24 inch soil profile). The 1988 drought was extreme, and 2021 has rivaled that in some locations. Based on previous drought years, it will be no surprise to find wheat fields with 80-100 lb/acre nitrate-N (0-24 inch soil profile) or even higher.

Past experience also shows us that drought can create greater crop yield variability across fields. Some zones in the field with better water holding capacity and soil organic matter may have produced a decent crop yield, and these will have lower residual soil nitrate-N. Yet, other zones may have had very poor crop growth and yield, leaving very high amounts of soil nitrate-N remaining.

Zone soil sampling is always a good idea, but it is especially important in drought years. Soil sampling based on productivity zones is the only way to determine the correct amount of nitrogen fertilizer in each zone across the field. To create good productivity zones for soil sampling, it is best to use multiple data layers such as satellite imagery, crop yield maps, topography, or electrical conductivity (Veris or EM38).

This fall, we expect residual soil nitrate-N to be higher than normal, but there will be exceptions to the rule. Last spring, there was a lot of broadcast urea fertilizer applied without incorporation. If no rain was received for several weeks after application, much of the nitrogen could have been lost to ammonia volatilization. This means some fields will seem out of place with lower residual soil nitrate-nitrogen because fertilizer nitrogen was lost last spring.

For fields with more than 150 lb/acre nitrate-N (0-24 inch soil profile), the crop nitrogen requirement for next year may not call for much, if any, nitrogen fertilizer. We must remember that drought creates variability within a field and even within large productivity zones. This is why we always suggest applying a base amount of nitrogen fertilizer to address the variability, even if the soil nitrate test is more than 150 lb/acre nitrate-N. A base nitrogen fertilizer rate (maybe 20 to 40 lb/acre N) should address most of the field variability and provide a fast start to the next year’s crop. In 1988, we learned the tough lesson that applying no nitrogen fertilizer on fields testing very high for nitrate-N was a mistake, and the best producing parts of fields had early-season nitrogen deficiencies. A modest base nitrogen fertilizer rate was the right decision to cover field variability.

Three Simple Lessons from Droughts Past

  1. Soil test all fields for residual soil nitrate-N. There will be considerable variability from field to field and even zone to zone.
  2. The residual soil nitrate-N test allows you to reduce nitrogen fertilizer rates for next year, saving money on crop inputs for 2022.
  3. Remember to apply a modest base nitrogen fertilizer rate on fields testing very high in nitrate-N to address field variability. You will want to get next year’s crop started right.

Update: Feed Nitrate Testing in a Drought Year

Drought continues to stress crops across the upper Midwest and the Canadian Prairies. As crop conditions continue to deteriorate in some places, we have received more phone calls about salvaging the drought-stressed crop as livestock feed and the need for feed nitrate testing. As you consider what to do with your standing crop, whether to harvest for grain or cut for hay, an important part of that consideration will be the nitrate concentration of the crop.

When drought-stressed annual crops (e.g., wheat, barley, oat, corn) are cut or grazed, producers must exercise caution about livestock nitrate poisoning when feeding these forages. Drought-stressed crops often accumulate nitrate because plant uptake of nitrate exceeds plant growth and nitrogen utilization. Nitrate is usually concentrated in lower plant parts (lower stem or stalk). When livestock, particularly sheep and cattle, ingest forages with a high nitrate concentration, nitrate poisoning can occur.

Instructions for collecting and submitting a feed nitrate test

1. Collect the plant part that livestock will consume, which may be the whole aboveground plant. If grazing, be mindful of the grazing height because the plant nitrate concentration will be lower near the base of the plant. If baling for hay or chopping for silage, cut at the intended cutter bar height.

Picture used for feed nitrate email - corn collage

2. Cut plant material with sturdy garden shears into 1- to 2-inch pieces. Mix the chopped plant parts together and take one quart-sized subsample for analysis (about four good handfuls).

3. Place subsample in AGVISE Plant Sample Bag. Write “Feed Nitrate” as the crop choice and select “Nitrate-nitrogen” as the analysis option.

    • If you are considering chopping corn for silage, also write “%Moisture” as an additional analysis because you will need to know if the moisture content is still adequate for silage fermentation. You may be surprised how much water will still be in drought-stressed corn stalks.

4. Ship plant sample to AGVISE Laboratories. If you cannot ship the sample right away, store it in a refrigerator until you can ship it.

IMPORTANT: Resample the hay or silage before feeding to any livestock. You need to know what is actually being fed to livestock, and you may need to blend it with other feed sources to dilute the nitrate concentration. For dry hay in bales, the nitrate concentration will not change in storage; use a hay probe to obtain the best possible feed sample. For silage, the nitrate concentration may decrease 20 to 50% during fermentation, so a fresh sample is necessary before feeding.

IMPORTANT: Many crop protection products have grazing restrictions on their labels that dictate if or when a crop treated with a product can be fed to livestock. Before using or selling a crop for livestock feed, check all labels of crop protection products that have been used on the crop this season. This includes seed treatments, herbicide applications, fungicide applications, and insecticide applications.

AGVISE Laboratories offers next-day turnaround for feed nitrate analysis. Rapid turnaround on nitrate analysis is important for producers debating to cut and bale or graze small grains or corn as livestock feed.  We also provide livestock water analysis, which includes total dissolved solids, nitrate, and sulfate, to assess livestock drinking water quality. Please call AGVISE staff in Northwood, ND (701-587- 6010) or Benson, MN (320-843-4109) with questions about nitrate, feed and hay quality, or water analysis. We can send you sampling supplies if needed.

AGVISE Laboratories Online Supplies Store

Helpful resources on using drought-stressed crops for livestock feed:

Nitrate Poisoning of Livestock (NDSU)

Using Drought-Stressed Corn as Forage (SDSU)

Drought-Related Issues in Forage, Silage and Baleage (Univ. of Missouri)

Potassium and Drought: A Two-fold Water Uptake Problem

Potassium is back on the radar for many farmers and agronomists across the upper Midwest and northern Great Plains. In the past two weeks, corn growth and development have reached the stage where potassium deficiencies are becoming quite apparent, and widespread dry soil conditions during the 2021 drought have worsened the problem. In some instances, corn is displaying potassium deficiency symptoms on soils with medium to high soil test K (120 to 180 ppm) in spite of potassium fertilizer application.

Potassium is required in large quantities for plant growth and development. The plant tissue K range in normal corn plants is 3-5% K, which is similar to nitrogen. A 200-bushel/acre corn crop will typically uptake 200 lb N, 108 lb P2O5, and 280 lb K2O per acre through the growing season (IPNI, 2014). In other words, an actively growing corn crop takes a lot of potassium! Luckily, you do not have to apply all that potassium as fertilizer, and much will come from the plant-available K pool in the soil.

Potassium deficiency in corn. Symptoms are leaf chlorosis (yellowing) and necrosis (death) beginning at the leaf tip and outer leaf margin and progressing toward the midrib, often with wavy leaf edges. Potassium is mobile in the plant, so symptoms appear on the lower leaves first as the plant remobilizes potassium from lower leaves to support new plant growth. 

Drought reduces potassium availability

The plant-available K pool becomes less available when soil water is limited. This has become the top story as the 2021 drought has continued. Plant roots acquire potassium mostly through a process called diffusion. Diffusion is the slow movement of ions through water around soil particles to the plant root for uptake. As soil becomes drier, the thickness of the water film around soil particles becomes thinner and thinner, thus the diffusion path for potassium ions becomes longer and longer. The soil pore space becomes mostly air with little water remaining. This ultimately slows the rate at which potassium from soil or fertilizer can reach the plant root, and potassium deficiency may occur.

The consequence of the drought-induced potassium deficiency is two-fold because potassium also plays an essential role in plant water regulation. Potassium-stressed plants experience reduced photosynthesis and transpiration rates, resulting in poor water use efficiency of the already limited soil water that is available. In a nutshell, low soil water content reduces potassium availability from soil and fertilizer, and then the soil water that is there is poorly utilized because of the lack of potassium. In addition to limited soil water, other factors compound to reduce potassium uptake: soil test K, soil texture, clay mineralogy, soil compaction, and even fluffy soil syndrome.

Believe it or not, fluffy soil syndrome has been a component of more than one phone call concerning potassium deficiency. Do you see greener plants near the planter wheel tracks or sprayer tracks? Fluffy soil syndrome occurs when soil has not completely settled since spring tillage, which results in poor soil particle-to-particle contact and slow soil-water-root diffusion routes for potassium ions. The wheel tracks adequately firmed the soil to provide good soil particle-to-particle contact, maintaining better potassium diffusion.

Potassium deficiency in corn: A case study

In June 2021, AGVISE started to receive plant and soil samples to diagnose suspected potassium deficiencies in various crops. This corn example from west central Minnesota included plant and soil samples collected in the good and poor areas of the field. The leaf K concentration was 0.59% in the good and 0.52% in the poor area. For comparison, the corn leaf K sufficiency range at this growth sage should be 2-3% K. The corresponding soil samples had soil test K at 148 ppm in the good and 140 ppm in the poor area. The soil test K critical level for corn is 150-200 ppm, and the farmer had applied 50 lb/acre K2O broadcast + incorporation, which is very close to the university sufficiency guideline for corn. Although the farmer more or less did everything right for a normal rainfall year, drought conditions have reduced potassium availability to the point where potassium deficiency symptoms were apparent and visible.

One week after the plant and soil samples were collected, the field received an inch of rain, and the potassium deficiency symptoms disappeared! The entire corn field is green now. It is amazing what a little water will fix.

Potassium deficiency in corn confirmed with plant and soil analysis. Potassium-deficient corn plant (left) displays chlorosis and necrosis of the outer leaf margin and wavy leaf edge. Plant and soil samples were collected June 2021 in west central Minnesota.

Correcting the problem

So, what do you do next? Do you try to apply an in-season rescue potassium fertilizer application? You still need rain to water in any fertilizer applied to the soil surface. If you had applied an adequate amount of potassium fertilizer before planting, then the appropriate decision is to wait for rain to improve soil and fertilizer potassium availability. However, some people may not have applied enough potassium initially. In these cases, a rescue application of 60 lb/acre K2O broadcast (100 lb/acre potash, 0-0-60) followed by some rain should correct the symptoms. Do not skimp with anything less because you are already behind the eight-ball and you will need that much material to cover the soil surface adequately and affect enough individual corn plants. In NDSU research (2014-2016), an uncorrected potassium deficiency in corn could cost 20-30 bushel/acre compared to corn receiving adequate potassium fertilizer.

For liquid materials, potassium acetate and potassium thiosulfate could be dribbled between the rows, but the potassium rate will need to be similar to the dry potassium fertilizer rate and cost will likely be greater. Remember, potassium is something required in large quantities, not something corrected with a small application of 5-10 lb/acre K2O.

There is no way we could have planned for the very dry conditions that are exacerbating potassium deficiency symptoms across the region. For the future, the best preventative strategy is precision soil sampling (grid or zone) and fertilizing accordingly. It is important to identify and address those parts of fields where potassium may be limiting crop yield potential and spend fertilizer dollars where needed.

Feed Nitrate Testing in a Drought Year

Drought is an unwelcome but well-known phenomenon on the Northern Plains and Canadian Prairies. Rainfall has been sparse and scattered across the region, and high temperatures exceeding 90 to 100° F (32 to 38° C) have already caused stress to young crops. These same stresses have also wracked pastures, prompting livestock producers to think about alternative feed options for cattle. Believe it or not, we have already received questions from farmers and ranchers about decisions to cut and bale or graze small grain fields for livestock feed.

When drought-stressed annual crops (e.g., wheat, barley, oat, corn) are cut or grazed, producers must exercise caution about livestock nitrate poisoning when feeding these forages. Drought-stressed crops often accumulate nitrate because plant uptake of nitrate exceeds plant growth and nitrogen utilization. Nitrate is usually concentrated in lower plant parts (lower stem or stalk). When livestock, particularly sheep and cattle, ingest forages with a high nitrate content, nitrate poisoning can occur if large amounts of nitrate convert to nitrite in their digestive system.

Dry soil conditions and high soil nitrate levels favor plant accumulation of nitrate. There is one upside to very dry soil conditions: Some soils may not have had enough soil water to convert all nitrogen fertilizer from the ammonium form to the nitrate form, especially if nitrogen fertilizer was applied in a concentrated band that delays nitrification. Therefore, this may limit the amount of soil nitrate available for plant uptake and accumulation. Regardless, there is still variation across the landscape, and a feed nitrate analysis is the best method to assess livestock nitrate poisoning risk.

When collecting plant material for nitrate analysis, collect the plant parts that the livestock will eat. If plant material will be grazed, recall that lower plant parts contain higher nitrate concentrations; monitor grazing height closely. If plant material will be cut and baled, you should collect plant material above the cutter bar height. Alternatively, plant material can be sampled with a hay probe after being baled.

For the fastest turnaround, submit feed materials for nitrate analysis using a plant sample bag. Write “feed nitrate” for crop choice and select “nitrate-nitrogen” as the analysis option. 

AGVISE Laboratories offers next-day turnaround for feed nitrate analysis. Rapid turnaround on nitrate analysis is important for producers debating to cut and bale or graze small grains or corn as livestock feed.  We also provide livestock water analysis, which includes total dissolved solids, nitrate, and sulfate, to assess livestock drinking water quality. Please call AGVISE staff in Northwood, ND (701-587- 6010) or Benson, MN (320-843-4109) with questions about nitrate, feed/hay quality, or water analysis. We can send you sampling supplies if needed.

AGVISE Laboratories Online Supplies Store

Scouting Shorts: Soybean Iron Deficiency Chlorosis (IDC)

As soybean plants emerge and add trifoliate leaves, keep your eyes peeled for soybean iron deficiency chlorosis (IDC). Through the upper Midwest and into the Canadian Prairies, soils with high pH and calcium carbonate pose a special problem for soybean plants and iron uptake. If you encounter soybean IDC, you will start to notice soybean plants with distinct interveinal chlorosis (yellow leaf with green leaf veins) in the newest leaves. The unifoliate leaves typically remain green.

Look for characteristic symptoms of soybean IDC (above photo).

When to scout

Right now! Soybean IDC symptoms begin to appear as soybean plants enter the first- to third-trifoliate leaf stage. You will often see soybean IDC symptoms appear after a period of cool, wet weather.

Where to look

Soybean IDC symptoms are usually confined to soybean IDC hotspots with high carbonate and salinity. Soil pH is not a good indicator of soybean IDC risk because some high pH soils do not have high carbonate or salinity, which are the two principal risk factors. The soybean IDC hotspots often occur on landscape positions with moderate to poor drainage, but soybean IDC symptoms may appear across the entire field if high carbonate and salinity are present throughout the field. High residual soil nitrate-nitrogen can also make soybean IDC worse, so take an extra look at fields that were fallowed last year (e.g. Prevented Planting) and had higher soil nitrate-nitrogen than normal.

What soybean IDC can be confused with

Nitrogen deficiency: Pale green and yellowing is uniform across the entire leaf and veins (not interveinal like soybean IDC). Yellowing appears on older leaves. It is sometimes observed when poor inoculation or delayed nodulation occurs. Look at soybean roots for active nodules (bright pink-red center) or take plant and soil samples to confirm.

Potassium deficiency: Yellowing starts at the outer leaf margin, works its way inward with some brown mottling. Yellowing appears on older leaves during early growth stages and sometimes on upper leaves during pod fill. Take plant and soil samples to confirm.

Soybean cyst nematode (SCN): Aboveground symptoms are virtually invisible during the early growing season. Visual SCN symptoms only occasionally appear in late July or August, or if dry soil conditions occur. Look at soybean roots for small white-colored SCN cysts or take an SCN soil sample including infected root material to confirm.

More information on soybean IDC symptoms, causes, and management: https://www.agvise.com/soybean-iron-deficiency-chlorosis-symptoms-causes-and-management/

Sidedress Corn Using the Pre-sidedress Soil Nitrate Test (PSNT)

As the corn crop begins to emerge, it is time to prepare for sidedress nitrogen applications. Sidedress nitrogen for corn can be applied any time after planting, but the target window is generally between growth stages V4 and V8, before rapid plant nitrogen uptake occurs. Split-applied nitrogen has become a standard practice in corn to reduce in-season nitrogen losses on vulnerable soils, such as sandy and clayey soils. More and more farmers now include topdress or sidedress nitrogen as part of their standard nitrogen management plan. These farmers have witnessed too many years with high in-season nitrogen losses through nitrate leaching or denitrification.

The target timing for PSNT sampling is when corn is 6 to 12″ tall. Twelve-inch corn is often V4 or V5 (like in the picture above). Do not hesitate in collecting soil samples for the PSNT; the target window for sidedress-nitrogen applications in corn is between the V4 and V8 stages. 

Whether your nitrogen management plan includes a planned sidedress nitrogen application or not, the Pre-Sidedress Soil Nitrate Test (PSNT) is one tool to help make decisions about in-season nitrogen. You may also hear this test called the Late-Spring Soil Nitrate Test (LSNT) in Iowa. PSNT is an in-season soil nitrate test taken during the early growing season to determine if additional nitrogen fertilizer is needed. PSNT helps assess available soil nitrate-nitrogen prior to rapid plant nitrogen uptake and the likelihood of crop yield response to additional nitrogen.

The Pre-sidedress Soil Nitrate Test (PSNT), taken when corn is 6 to 12 inches tall, can help you decide the appropriate sidedress nitrogen rate. The PSNT requires a 0-12 inch depth soil sample taken when corn plants are 6 to 12 inches tall (at the whorl), usually in late May or early June. Late-planted corn may not reach that height before mid-June, but PSNT soil samples should still be collected during the first two weeks of June. The recommend soil sampling procedure requires 16 to 24 soil cores taken randomly through the field, staggering your soil cores across the row as you go. All soil cores should be placed in the soil sample bag and submitted to the laboratory within 24 hours or stored in the refrigerator.

You can submit PSNT soil samples using the online AGVISOR program by choosing the “Corn Sidedress N” crop choice and submitting a 0-12 inch soil sample for nitrate analysis. AGVISOR will generate sidedress nitrogen fertilizer guidelines, using the PSNT critical level of 25 ppm nitrate-N (0-12 inch depth). If PSNT is greater than 25 ppm nitrate-N, then the probability of any corn yield response to additional nitrogen is low. If spring rainfall was above normal, then the PSNT critical level of 20 to 22 ppm nitrate-N (0-12 inch depth) should be used. Iowa State University provides additional PSNT interpretation criteria for excessive rainfall, manured soils, and corn after alfalfa.

If the PSNT is taken after excessive rainfall, the soil cores will be wet and difficult to mix in the field. Therefore, it is best to send all soil cores to the laboratory to be dried and ground, ensuring a well-blended soil sample for analysis. Although in-field soil nitrate analyzers have improved over the years, the difficult task of blending wet, sticky soil cores in the field still remains. The only way to get accurate, repeatable soil analysis results is to dry, grind, and blend the entire soil sample in the laboratory before analysis. AGVISE provides 24-hour turnaround on PSNT soil samples. The soil samples are analyzed and reported the next business day after arrival. Soil test results are posted on the online AGVISOR program for quick and easy access. With AGVISE, you get not only great service but also the highest quality data with four decades of soil testing experience.

Pre-Sidedress Soil Nitrate Test (PSNT) resources

Please call our technical support staff if you have any questions on PSNT and interpreting the soil test results for sidedress nitrogen application.

Protect Nitrogen Fertilizer from Ammonia Volatilization

Recent rain and snow have brought much-needed precipitation to the northern Great Plains and upper Midwest regions. Some degree of drought conditions stretch from Alberta to Iowa, and agronomists and farmers are wondering the best ways to protect spring-applied nitrogen as the planting season continues. How much nitrogen might I lose if I cannot incorporate it? Does vertical tillage incorporate fertilizer enough? We have compiled some resources to help answer those questions.

There are three ways to lose fertilizer nitrogen: ammonia volatilization, denitrification, and nitrate leaching. In excessively wet soils, denitrification and nitrate leaching are a concern. However, for spring-applied nitrogen, ammonia volatilization is the main concern with dry soil conditions and unpredictable rainfall forecasts.

When you apply ammoniacal fertilizers (e.g. anhydrous ammonia, urea, UAN, ammonium sulfate) to the soil surface without sufficient incorporation, some amount of free ammonia (NH3) can escape to the atmosphere. Sufficient incorporation with tillage or precipitation is needed to safely protect that nitrogen investment below the soil surface. With dry soil conditions, this is important to remember because we must balance the need to protect nitrogen fertilizer while conserving soil water for seed germination and emergence.

Ammonia volatilization risk depends on soil and environmental factors (Table 1) and the nitrogen fertilizer source (Table 2). Typically, we are most concerned about ammonia volatilization for surface-applied urea or UAN. It is not easy to estimate how much nitrogen might be lost, and sometimes the losses can be substantial. Although you cannot change the soil type or weather forecast, you do have control over the nitrogen source and application method (Table 2) to protect your nitrogen investment.

Practices to reduce ammonia volatilization, in order of most effective: 

  • Apply urea in subsurface bands at least 3 inches below the soil surface. A shallow urea band (1 or 2 inches) acts like a slow-release anhydrous ammonia band, and nobody should ever apply anhydrous ammonia that shallow.
  • If nitrogen will be broadcast with incorporation, make sure the fertilizer is sufficiently incorporated at least 2 inches below the soil surface to ensure good soil coverage. A chisel plow or field cultivator is usually needed. The popularity of high-speed disks (vertical tillage) has led some people to think that it counts as a meaningful incorporation event. In reality, it just moves soil and crop residue around on the soil surface without really incorporating any fertilizer. Take a look after you run across the field and you will see white urea granules everywhere. There are soil-applied herbicide incorporation videos from the 1970s that show what a thorough incorporation job really requires.
  • If nitrogen will be broadcast without incorporation, try to time the fertilizer application right before rain (at least 0.3 inch of precipitation). Soils with good crop residue cover (no-till) may require more rain to sufficiently move urea or UAN into the soil surface.
  • If no rain is forecasted in the near future, consider applying a urease inhibitor on urea or UAN to provide temporary protection until rain arrives. The university research-proven urease inhibitor is NBPT, available in products like Agrotain (Koch) and its generic cousins. For generic products, make sure the active ingredient rate is 1.3 to 1.8 lb NBPT per ton of urea to ensure effective NBPT activity and protection. NBPT begins to breakdown after 7 to 14 days. In addition, it is important to remember that nitrification inhibitors like nitrapyrin and DCD do not protect against ammonia volatilization.

These practices should also be considered if you will be applying in-season nitrogen to corn or wheat later in the summer. it is always best to apply nitrogen below the soil surface, such as injected anhydrous ammonia or coulter-injected UAN, to protect nitrogen fertilizer. For surface-applied urea or UAN, you will want to time the fertilizer application just before a rainfall or consider NBPT to extend the rainfall window.

Resources on ammonia volatilization and urease inhibitors

Nitrogen extenders and additives for field crops, NDSU

How long can NBPT-treated urea remain on the soil surface without loss?, NDSU

Should you add inhibitors to your sidedress nitrogen application?, University of Minnesota

Split the risk with in-season nitrogen, AGVISE

Adjusting high soil pH and salinity with sugar beet-processing spent lime

The sugar beet processing industry uses large quantities of fine-ground, high-grade calcium carbonate (lime) to purify sucrose in the sugar extraction process. The by-product spent lime retains high reactivity and purity, making it an attractive liming material for acidic soils. Application of spent lime is a common practice through the sugar beet producing areas of the upper Midwest and northern Great Plains, where its primary function is the suppression of the soil-borne disease Aphanomyces root rot of sugar beet. The spent lime also contains about 20 lb P2O5 per ton, mostly as organic phosphorus impurities gained from sugar refining.

We often get questions about correcting high soil pH and salinity with spent lime. Salt-affected soils, saline and sodic, are a common problem across the northern Great Plains. These soils have high soil pH and present numerous agronomic and soil management problems. The soil amendment gypsum (calcium sulfate) is often applied to sodic soils (those with high sodium) to combat soil swelling and dispersion. The spent lime (calcium carbonate) also contains calcium, but it is very insoluble at high soil pH.

Each year, we get many questions about applying spent lime on soils with high pH and salinity. To answer these questions, AGVISE Laboratories installed a long-term demonstration project in 2008 to evaluate adjusting high soil pH and salinity with spent lime. We applied multiple spent lime rates and tracked soil test levels over seven years. There were no significant changes or trends in soil pH (Table 1) or salinity (Table 2). This is no surprise because the initial soil pH was high and buffered around 7.8-8.2, indicating the presence of natural calcium carbonate. If the soil already contains naturally occurring lime, what is the good of adding more lime? Moreover, calcium carbonate is very insoluble, so there is no expectation that more lime will decrease or increase salinity.

Since soil test levels did not change over seven years, we terminated the project in 2014. The research question was a conclusive dud. While spent lime is useful to amend acidic soils and suppress Aphanomyces root rot of sugar beet, it does not help on soils with high pH or salinity.

 

 

Table 1. Soil pH (1:1) following sugar beet-processing spent lime application on high pH soil.
Spent Lime Year Average
2008 2009 2010 2011 2012 2013 2014
ton/acre
1 7.8 7.7 7.9 7.8 7.7 8.0 8.0 7.80
2 7.9 7.9 8.1 7.9 7.9 8.0 8.0 7.94
3 7.9 7.9 8.1 7.9 7.9 8.1 8.1 7.95
4 7.8 7.8 7.9 7.7 7.8 8.1 8.0 7.85
5 7.8 7.8 8.0 7.9 7.9 8.0 8.0 7.90
6 8.0 7.9 8.2 8.0 8.0 8.1 8.1 8.00
Spent lime applied and incorporated September 2008. Soil sampled in fall.

 

Table 2. Soil salinity (electrical conductivity, EC 1:1) following sugar beet-processing spent lime application on moderately saline soil.
Spent Lime Year
2008 2009 2010 2011 2012 2013 2014
ton/acre ——————— dS/m ———————
1 1.5 1.2 1.8 1.1 1.6 1.2 1.8
2 1.9 2.1 2.3 2.5 2.3 2.0 2.0
3 1.9 2.2 2.6 2.5 2.4 1.9 1.9
4 1.0 1.3 1.4 1.2 1.5 1.9 1.9
5 1.7 2.2 2.2 2.3 2.2 1.7 1.7
6 2.6 2.1 2.1 2.9 2.5 1.9 1.9
Spent lime applied and incorporated September 2008. Soil sampled in fall.

Uffda, that’s a lot of potash!

Question: Can you really change the %K base cation saturation ratio?

This winter, we have gotten more questions from farmers asking about the base cation saturation ratio (BSCR) concept. The farmers had attended a series of meetings where the speakers encouraged farmers increase the %K saturation in their soils and apply high potassium fertilizer rates to soils, even though there was little to no chance to get a crop yield response. In short, the BSCR concept revolves around reaching a certain percentage (%) of each base cation in your soil to obtain the “ideal” soil. If you do not have the right percentage of each cation, then you are instructed to apply large amounts of fertilizer to reach this “ideal” balance of each cation. Potassium is the most common nutrient where people fall into the BSCR trap, often suggesting that extra potassium will “fix” their soil.

Since the 1940s, university and industry researchers from around the world have thoroughly debunked the BCSR concept. But sometimes, you just need to show people how this works in the real world to get their attention. To help farmers see the silliness of the BSCR concept, we conducted a simple field project in 2015 to show just one flaw in the failed BSCR concept, focusing on its primary claim that you can actually change the %K saturation in soil. We identified three soils in Manitoba, Minnesota, and North Dakota with low initial %K saturation. The goal was to increase %K saturation into the 4 to 6% range, which is recommended by BCSR promoters. We applied a staggering rate of 1000 lb/acre K2O (1666 lb/ acre potassium chloride, KCl, 0-0-60). You are probably thinking that 1000 lb/acre K2O is a lot of potash! And so did we. We called the project the “uffda” project because my Norwegian grandfather, who farmed in southern Minnesota 60 years ago, would have looked at the high rate and said, “Uffda, that’s a lot of potash!”

But, we failed to achieve the “ideal” 4 to 6% K saturation (Table 1). As expected, soil test K (part per million, ppm) increased substantially, but the %K saturation did not reach the “ideal” soil range even with the enormous potassium fertilizer rate.

Table 1. Soil test potassium and potassium base saturation after application of 1000 lb/acre K2O (1666 lb/acre potassium chloride, KCl, 0-0-60).
Location Soil test K, ppm K saturation, %
initial final initial final
Northwood, ND 156 430 0.6 1.6
Benson, MN 154 290 1.9 3.7
Roseisle, MB 50 330 0.4 2.8

Do you need more proof? Let’s see what the plants said. The soybean plant tissue K concentrations did not change either because the soil test K (ppm) was sufficient and above the 150 ppm critical level (Table 2). Simply put, the proven university-developed soil fertility guidelines would have told you that more potassium was not needed. I know a few farmers who were convinced to follow the BCSR concept, which only wasted their valuable dollars and time on the failed idea.

Table 2. Soybean leaf potassium concentration did not increase with additional potassium fertilizer applied on soils with soil test potassium above the critical level (150 ppm).
Fertilizer K Rate Soybean leaf K, %
lb/acre K2O Northwood, ND

STK 150 ppm

Benson, MN

STK 190 ppm

0 3.2 1.9
20 2.6 1.8
100 2.7 1.8
200 3.0 1.8
1000 2.6 1.9
Soybean leaf K sufficiency level = 1.7 %K

All things considered, there are still good reasons to apply potassium fertilizer (moderate rates) to achieve profitable yield responses. Either way, the base cation saturation ratio (BCSR) concept is a really bad way to justify potassium fertilizer use, and it usually leads to very high fertilizer rates and costs. Here are some good reasons to include potassium in your soil fertility program:

  • Soil test K below 150 ppm (grid or zone soil test)
  • Soil test K below 200 ppm (composite soil test, high soil variability)
  • History of low plant tissue K when no potassium fertilizer is applied; potential compaction
  • Replicated strip trials showing profitable crop yield response to moderate potassium fertilizer rates
  • Chloride required for small grains; potassium chloride (0-0-60-50Cl) is the most common chloride source

Starter Fertilizer Display: How low can YOU go?

When profits are squeezed, more farmers are asking about optimal starter fertilizer rates and how low starter fertilizer rates can be. These questions are the result of wanting to keep fertilizer costs down, to plant as many acres per day as possible, and to take advantage of more efficient, lower rates of banded phosphorus fertilizer compared to higher rates of broadcast phosphorus fertilizer.

To illustrate the role of starter fertilizer rates and seed placement, we put together displays showing the distance between fertilizer granules or droplets at various rates and row spacings. You can see several pictures with canola, corn, soybean, sugar beet, and wheat. We greatly thank John Heard with Manitoba Agriculture for helping with the displays.

The displays show the normal seed spacing for several crops with different dry or liquid fertilizer rates alongside the seed. These displays help visualize the distance between the seed and fertilizer at several rates. University research shows that to achieve the full starter effect, a fertilizer granule or droplet must be within 1.5-2.0 inches of each seed. If the fertilizer granule or droplet is more than 1.5-2.0 inches away from the seed, the starter effect is lost. Some people wonder about these displays, but you can prove it to yourself pretty easily. Just run the planter partially down on a hard surface at normal planting speed. You will see what you imagine as a constant stream of liquid fertilizer, ends up being individual droplets at normal speed, especially with narrow row spacings and lower fertilizer rates.

These displays help illustrate the minimum starter fertilizer rate to maintain fertilizer placement within 1.5-2.0 inches of each seed for the full starter effect. In addition to an adequate starter fertilizer rate, additional phosphorus and potassium should be applied to prevent nutrient mining, causing soil test levels to decline in years when minimum fertilizer rates are applied.