Which Fertilizer Should Corn Producer Use As Starter: 10-34-0 Rr 32-0-0?
RASEL PARVEJ
BATON ROUGE, LOUISIANA
Louisiana corn producers mostly use ammonium polyphosphate such as 10-34-0 or 11-37-0 as starter fertilizer and apply it in the seed furrow or in a 2 by 2 band. These starter fertilizers mostly contain small amounts (10 or 11 percent) of nitrogen (N) and high amounts (34 or 37 percent) of phosphorus (P2O5). Starter fertilizer is usually applied at a lower rate (5 gal/acre) for in-furrow application due to the chance of salt injury from ammonium-N (NH4+-N) but can be applied at a higher rate (up to 10 gal/acre) for 2 by 2 banding or dribbling.
Although adequate soil moisture at planting can reduce the likelihood of salt injury, high rates of N fertilizer is still not recommended for in-furrow application.
The main purpose of applying starter fertilizer is to help the germinating corn seedling boost up early-season growth by easily accessible nutrients placed near the seeds, resulting in increased yield potential. However, corn grain yield response to 5 gal/acre of 10-34-0 or 11-37-0 starter fertilizer is very inconsistent with no yield response being common across the mid-South and Midwest. Mascagni et al. (2007) conducted 15 site-years research trials from 1991 to 2005 on starter fertilizer (10-34-0 or 11-37-0) for corn production in northeast Louisiana and found that starter fertilizer increased corn yield by 8 to 25 bu/acre in only 5 out of 15 trials (i.e., 33 percent accuracy; Fig. 1). They reported that the positive yield response to starter fertilizer came only from phosphorus (P) but not from nitrogen (N). This was because 5 gal/acre of in-furrow starter fertilizer (10-34-0) contains 19.8 lbs P (P2O5) but only 5.8 lbs N per acre, which is a very small amount to make any yield difference by N at planting.
The most important point that Mascagni et al. (2007) reported was that starter fertilizer increased corn yield only in coarse-textured soils such as sandy loam soils. They also reported that sandy loam soils were cold-natured soils with low organic matter content and nutrient holding capacity, where P deficiency symptoms were common early in the growing season (mid-March to mid-April). Cold soil temperature often causes reduced P uptake by young corn plants, due to slow root growth, resulting in temporary P deficiency especially in sandy loam soils, even though soil-test P levels are adequate (21 to 35 ppm P or 42 to 70 lb/acre P at 0- to 6-inch soil depth). However, this early season P deficiency especially in soils with sufficient P level can go away with warmer soil temperature and adequate moisture and usually does not negatively affect corn yield. If the Mehlich-3 soil-test P level is low (less than 21 ppm or 42 lb/acre) and producers already applied P fertilizer either in the Fall or Spring, there may be no benefit of using 10-34-0 or 11-37-0 starter fertilizer. This is also true for high P testing soils (more than 35 ppm or 70 lb/acre P) where additional P is not needed. For medium testing soils (21 to 35 ppm or 42 to 70 lb/acre), if producers do not apply any P fertilizer, there may or may not be a benefit of using 10-34-0 or 11-37-0 starter fertilizer especially in coarse-textured soils with early planting. No yield benefit from these starter fertilizers is common for corn production in fine-textured soils such as clayey soils. Since fertilizer-P when applied in soils can be fixed to unavailable forms as aluminum phosphate when soil pH falls below 5.5 and as calcium phosphate when soil pH exceeds 7.5, starter fertilizer 10-34-0 or 11-37-0 that mostly contains P, may be beneficial to ensure maximum fertilizer-P availability for early-season plant uptake especially for soils with pH outside of this range (6.0 to 7.5), deficient in soil-P, and no P fertilizer is applied during the Fall or Spring.
Corn requires 30 to 45 lbs N from planting to V6 stage (6 visible collar leaves and plant is about 12-18 inches tall) and this N requirement can only be fulfilled by either applying 65 to 98 lbs of urea (46-0-0) or 8.5 to 12.7 gals of UAN (32-0-0) per acre at planting. Urea (46-0-0) should be broadcasted followed by incorporation at or before planting. UAN (32-0-0) can be applied as 2 by 2 banding or dribbling at planting. If 10-34-0 or 11-37-0 starter fertilizer is used, producers need to apply 26 to 39 gals/acre to fulfill the 30 to 45 lbs N requirement at planting, which would not be economically sound since fertilizer price is at a record high. In addition, when corn is planted in high plant residue with or without cover crops, this high plant residue sometimes results in early-season N deficiency due to N immobilization by soil microbes. Providing 30 to 45 lbs of N using 32-0-0 during planting as a starter would offer more benefits in these soil conditions than 5.8 lbs of N using 10-34-0 or 11-37-0.
Overall, producers should use 32-0-0 (30-0-0-2S or 28-0-0-5S can also be used if 32-0-0 is not available but the rates need to be adjusted) as a starter fertilizer during corn planting to provide the need of 30 to 45 lbs N from planting to V6 stage and come back with the rest of the N rate as a sidedress during V6-8 stages. Note that producers should subtract the starter N rate from the total N rate during sidedressing. The total N rate depends on corn yield goal and soil type. Corn requires 1 lb of N per bushel of yield for sandy to silty loam soils and 1.25 lbs of N per bushel of yield for clayey soils.
Therefore, producers should apply 30 lbs of N for sandy to silty loam soils and 45 lbs of N for clayey soils during planting (Please read the article “Optimum nitrogen rate and timing for Louisiana corn” for more information regarding optimum N rate and timing). ∆
Rasel Parvej, Syam Dodla, Matthew Foster, and Rezaul Karim Louisiana State University AgCenter Scientists
Figure 1. Corn yield response to starter fertilizer in research trials conducted by Mascagni et al. (2007) on Mississippi River alluvial sandy loam/silt soils at the Northeast Research Station in St. Joseph, Louisiana. [NS, not significant at the 0.05 probability level; Source: Mascagni (Rick), H.J., D. Boquet, and B. Bell. 2007. Influence of starter fertilizer on corn yield and plant development on Mississippi River alluvial soils. Better Crops. Vol. 91(2)]