When your potatoes need phosphorus, timing is everything

Nov 1, 2014

Potato Grower

Trudy Naugler Klassen, BSc., MSc., P.Ag., Agronomy Research Analyst at Ostara Nutrient Recovery Technologies Inc.

Timing is a critically important aspect of nutrient management. It impacts everything from crop health, to return on investment, to the environment. It’s no wonder that “Right Time” is one of the four pillars of 4R Nutrient Stewardship, in addition to Right Rate, Source and Place. For any nutrient, one of the main goals is to have the nutrient release and availability match with plant uptake as closely as possible. There needs to be sufficient nutrient availability for crop demand over the growing season, while minimizing soil nutrient loss.

Consider the timing aspect of phosphorus management for potato production. Phosphorus is an important nutrient for both potato yield and tuber quality. Potatoes can remove a considerable amount of P compared to other crops; for example, a 400-500 cwt/A yield could remove 60-80 lb P2O5/A. The majority of this P uptake occurs during the bulking growth stages, more than 40 days after emergence and continuing into the late bulking. The peak daily P uptake also occurs in this latter part of the season, meaning that the daily phosphorus uptake requirements are highest during bulking.

But how does phosphorus fertilizer timing match up with this nutrient uptake? We know recommended phosphorus application timing is generally at planting or early in the season, which seems ironic given that peak uptake occurs much later in the season. We also know that traditional phosphorus fertilizers are highly water soluble, dissolving quickly into the soil solution where they can undergo chemical reactions in the soil that can later limit the P availability to plants (calcium, aluminum, and iron are the most common elements that “tie up” soil P). If done in a timely manner before tissue levels have dropped below critical levels, in-season P applications can be of some help, but with phosphorus having limited mobility in the soil this is not as effective, especially if the roots are not close to the surface. When soil P concentrations fail to meet peak P demands, tuber size, yield and health can be diminished.

Recently, a new granular, slow-release, phosphorus fertilizer, Crystal Green®, entered the market that can help address some of these timing-related challenges. Crystal Green’s naturally slow release properties ensure P is released and available during peak uptake periods. The inherent solubility characteristics of the granule are responsible for the unique dissolution. Extremely low water solubility combined with citrate solubility results in a “plant-activated™” release – when roots come in proximity of the Crystal Green granules, they will directly replenish the soil solution while also having increased release due to organic acid root exudates. The result is sufficient phosphorus availability during critical stages such as bulking and maturation. In university trials, Crystal Green has shown to maintain critical petiole P concentrations throughout the season, as well as maximize marketable yield.

Applied as a preplant application or at planting, the nutrients from Crystal Green will release and be available at the right time due to the plant-activated, slow release characteristics, while mitigating the risks of runoff and leaching. As a 4R Nutrient Stewardship partner, Ostara Nutrient Recovery Technologies, the producers of Crystal Green, supports best management practices that enhance environmental protection, expand production, increase farmer profitability, and improve sustainability. Given the pressure on farmers and producers in the agricultural sector to reduce nutrient runoff, fertilizer technologies that help growers match nutrient release with crop nutrient demand provide an important tool to add to a growing arsenal of sustainable products and practices. Current research shows that the release properties of Crystal Green can help reduce the risks of phosphorus runoff to waterways, helping keep nutrients in the field, available for the crops that need it.

Combining Crystal Green with a traditional water-soluble phosphorus fertilizer can be a great strategy to match nutrient availability with crop demand throughout the season. The traditional P fertilizer will provide the early phosphorus availability that is critical to early plant growth and tuber set, and the Crystal Green will be releasing during peak uptake and bulking. This season long availability will be reflected in the petiole P concentrations, and most importantly in the marketable yield and premium tuber size.

For stewards of the land, crop nutrition is a fine balance of fertilizer rate, source, timing, and placement. Smart stewardship also means increasing the bottom line sustainably. Matching phosphorus release with potato crop demand is a means to maximize your phosphorus investment, by not only increasing the crop value with healthy, premium sized tubers, but by doing so to the benefit of the environment. Timing is everything, and utilizing best management practices that incorporate the 4R’s of nutrient stewardship are keys to increased efficiency and sustainable profitability.

Read this article in Potator Grower online.

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