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Fluid Journal : Fall 2010
Some studies have suggested that K may explain the early corn growth and yield response to starter in low-testing soils but provided poor evidence of a true starter K effect. Recent research with liquid 3-18-18 starter provided no clear clues, but suggested little or no true starter effects from K. Knowledge of the existence of a starter K effect, and the conditions in which it is more likely, is important to improve the efficiency and economics of fertilizer use. This is because many producers' fields test optimum or high in soil test K and most fertilization guidelines recommend starter for soils only under certain conditions. Another very important point to keep in mind for in-furrow starter application is that K compounds are the most common cause of salt damage, so some fluid fertilizers are expensive because they use low salt K compounds to minimize seedlings damage. A few decades ago starter fertilizers used in the Corn Belt were mostly granulated products, but use of liquid starter fertilizers predominates today. Larger corn planters have also brought about a steady change from the classic "2 x 2" placement method to in-furrow Fall 2010 The Fluid Journal 12 Iowa on-farm ﬂuid trials show mixed results regarding nutrient uptake, early growth, and actual grain yield after applying starter K. A Look At Effects Of In-furrow Applications Of Potassium On Corn The Fluid Journal • Ofﬁcial Journal of the Fluid Fertilizer Foundation • Fall 2010 • Vol. 18, No. 4, Issue #70 Dr. Antonio Mallarino, Mr. Nicolas Bergmann, and Dr. Daniel Kaiser Summary: Fluid starter containing potassium (K) and phosphorus (P) often increased early corn growth and uptake of both nutrients more than a higher broadcast rate, even in the high-testing soils, but this response did not translate into higher grain yield with starter. Starter K alone seldom increased early growth or K uptake (sometimes decreased it) and often increased early plant K concentration but this response often was not reflected in increased grain yield. Starter P-K or K applied in addition to broadcast fertilization never increased yield further. Larger and more frequent starter effects from P than from K are in agreement with results of basic studies conducted during the '70s and '80s, which showed a higher maximum root uptake rate for K than P in the nutrient- concentrated zone but more root proliferation for P. A grain yield response to broadcast fluid starter sometimes was observed in soils testing high in K, but not with soils high in P. An important result was that fluid starter often resulted in corn yield increases similar to those from much higher broadcast fertilizer rates. However, in-furrow starter was not an effective practice when it was applied in addition to broadcast P-K rates planned to maintain or build up soil test values for 2-year corn/soybean rotations. Placement of small amounts of nutrients in bands beside and below the seeds or in the seed furrow significantly increases the concentration of nutrients in the small soil volume where seedling roots grow. Common fluid starters are nitrogen (N)-P or NPK products or mixtures to which other nutrients often are added. Research summarized in thorough reviews indicates that starter fertilizer often increases early corn growth and nutrient uptake more than similar or higher broadcast rates. The growth response to starter usually is larger and more frequent where 1) conditions limit root growth or activity, 2) where there is concentration in the soil of nutrient forms plants can absorb, or 3) where there is nutrient diffusion to the root. Research has shown, however, that starter effects on grain yield are not consistent. Phosphorus is a relatively immobile nutrient, its diffusion to seedling roots is limited by cold soil temperature and it is critical for plants, especially during early growth. Research has shown that N also often explains corn response to starter, especially in soils testing high in P. application. Therefore, the goal of this study was to investigate corn response to in-furrow liquid starter K without the confounding effects of other nutrients. Small plot trials Early corn growth responded to one or more fertilizer treatments at five of six sites (Table 1). The only exception was site 1, under no-till management, where soil P was optimum, soil test for K was low (not shown), and the planting date was the latest of all the sites. Starter PK applied alone increased early growth in the five responsive sites while starter K alone increased growth in two sites but decreased it in three sites. Although the broadcast PK rate was almost ten times higher than the starter rate, broadcast fertilization alone increased growth more than starter PK only at site 4, while starter PK increased growth more than broadcast at site 5. Application of starter PK in addition to broadcast PK increased corn growth at sites 5 and 6 but starter K, in addition to broadcast fertilizer, never increased growth but decreased it at three sites. Therefore, the results demonstrated that starter P can stimulate early growth as much as or more than
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