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0309 PD: Potash may be impacting your dairy’s forage nutrient variability and rations

David Weber Published on 06 February 2009

There are many factors that influence forage variability. Weather, location and time of harvest are a few.

One other emerging factor influencing mineral levels in forages is the use of potash as a fertilizer source.

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Potash 101: The basics behind the fertilizer

Potash has been used as a common fertilizer source for hundreds of years. Up until the mid 1970s, almost all potash was potassium oxide, but essentially any potassium source was referred to as potash. Today, multiple potash sources exist, including potassium carbonate, potassium sulfate, potassium oxide and, as the rest of this article will discuss, potassium chloride. Potassium chloride appears to be the only source or at least the main source of potassium that is being used today in commercial fertilizers.

Potash has many favorable traits, especially that it provides high levels of potassium, which is essential for multiple aspects of proper crop growth, including:

Plant protection
Potassium serves as a protector of crops against disease and pests.

Weather adjustment
Supplemental potassium allows for plants to adjust to changing weather conditions.

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Nutrient absorption
High-quality potassium supplementation encourages nutrient absorption from the soil, resulting in larger, more nutritious crops.

The influence of potassium chloride
Potassium chloride became, and continues to be, a popular potash source because it is a cost-effective supply of key nutrients, providing high levels of potassium for use by the plant.

Producers often focus on the potassium supplied from the potash without paying close attention to the other nutrients, says Ev Thomas, a retired agronomist from the William H. Miner Agricultural Research Institute. As the compound name notes, potassium chloride is composed of two key nutrients, with 60 to 62 percent of the potash composed of potassium and the remaining made up solely of chloride.

How these two nutrients are absorbed by the plant and stay in the soil will ultimately influence soil composition, forage quality and the nutrients provided to the dairy cow ration. Here’s what we know about potassium and chloride and their role in the soil:

Potassium is readily taken up by the plant.
Plants, especially grasses, will take up as much potassium as they can. High uptake of potassium by this year’s crop can result in the need to apply potassium for next year’s crop, according to Thomas.

Some chloride can remain after harvesting, which increases the amount of chloride anions available to the plant from one crop harvest to the next.
Chloride will leach much more readily than potassium. While chloride levels can increase during the growing season, most would leach away over winter. Chloride levels will continue to increase in the soil since more potash is applied to meet plant potassium requirements.

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What potassium chloride potash means to your herd
By understanding how potassium and chloride perform in the field, producers can recognize how forage quality is influenced during harvest and feeding. Potassium and chloride are two of the macrominerals included in the dietary cation-anion difference (DCAD) equation. Both have scientifically been shown to influence cow performance and health.

Particularly in fresh cows, research shows how alarming forages high in chloride can be for performance and health. As Figure 1* illustrates, increasing levels of chloride in lactating diets has a negative effect on dry matter intake (DMI) and milk production. On both charts, the solid line shows cows’ response to rising chloride levels in winter weather while the dotted line accounts for cows’ response during summer months. Regardless of weather conditions, the research found lactating cows fed diets with higher chloride levels decreased DMI and milk production. To avoid these pitfalls, diets must be formulated to account for the variability in forage chloride levels to optimize milking string performance.

Chloride is continually recycled on the dairy, as shown in Figure 2*. Potassium exits the cows and the farm in many avenues, including animal perspiration and milk production. Chloride, on the other hand, does leave the dairy but at a slower rate, which means more chloride is left behind in manure and applied back onto the fields.

The rising chloride levels and the continuous potash supplementation have resulted in extreme forage variability when looking at macromineral levels. Our second annual forage testing program results (shown in Table 1* and Table 2*) found that producer forages had an average DCAD similar to book values, but the minimum and maximum values made forage especially variable. Some forages had chloride levels over 1 percent of ration dry matter, which can negatively affect lactating cow performance and health.

Maintain herd performance in the midst of variability
There are many opportunities to manage forages and fields, even when potash is applied. Thomas recommends the following:

Utilize forage testing
The only way to know your forage DCAD levels is through routine forage testing. Thomas notes that chloride levels are not always tested on standard forage analyses but can be provided for minimal cost now. To account for the chloride that may be regularly applied as a potash source, routine chlorine testing in all forages is advised. This information will allow ration formulation to meet cows’ needs.

Close-up cow rations should be formulated for a negative DCAD of -8 to -12 meq (milliequivalents ) per 100 grams (g) ration dry matter and lactating ration DCAD should be positively formulated for +35 to +45 meq/100g ration dry matter.

Include water in DCAD balancing.
It’s not uncommon for water to be high in chloride and also may be high in sulfur, which is also a negative ion. This means testing your water source is just as important as testing your forages. Remember to test all water sources, as chloride levels can change significantly even on the same farm. High levels of chloride in your water source should be accounted for when balancing DCAD levels in the diet.

Complete routine soil analyses.
Soil sampling is the best way to know which nutrients your fields need for optimal plant growth and productivity. This will provide information on the nutrients already in the soil and possibly identify high chloride levels. Work with your agronomist to match your soil profiles with fertilizer needs in the upcoming year.

Match feeds with stage of lactation.
High-chloride forages are suited for prefresh rations, says Thomas. This is due to the high anion levels, which decreases DCAD. After obtaining a wet chemistry forage analysis, work with your nutritionist to deliver the proper forages to the right groups of cows. Forages higher in potassium should be included in lactating rations, and those with high chloride levels should be in prefresh diets. Remember to measure both minerals in all forages.

When forages can’t provide the proper DCAD levels, supplemental feed ingredients that supply additional – potassium and sodium – and palatable anions – chloride and sulfur – may be necessary for lactating and close-up groups, respectively. The trick is to only add the ion you need. Adding salt will give both sodium and chloride and adding potassium chloride will provide both potassium and chloride.

Soil and forage variability continues to be a challenge for dairies today, especially when it’s your responsibility to provide dairy cows with a consistent feed source from one day to the next. Work with your nutritionist and agronomist to learn more about the influence of potash in your fields, forages and rations. PD

*References, tables and figures omitted but are available upon request at

David Weber
Field Technical Services for ARM & HAMMER
Animal Nutrition

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