Research on Corn Yield Response to Starter
Starter fertilizer applications to corn have been well researched and documented. The scientific literature shows numerous cases where starter has produced positive, meager and no corn grain yield increases. This array of results means that positive grain yield responses are likely related to both environmental and cultural interactions. Several important studies are discussed below.
Starter Research Results by Geography and Type of Nutrients in Starter
- Researchers in Minnesota found a corn grain yield response to nitrogen (N), phosphorus (P) and potassium (K) starter fertilizer regardless of tillage practices. (Vetsch and Randall, 2002). These and other research results suggest that the primary geographic region that might consistently and positively respond to starter fertilizer are areas of the northern Corn Belt.
- In the central and northern Corn Belt states of Illinois, Wisconsin and Iowa, researchers found similar results when N, P, and K starter fertilizers were used. However, grain yield increases were much more consistent in soils that were low testing for P, poorly drained, or managed with no-till or reduced tillage (Wolkowski, 2000; Mallarino et al., 1999; Randall and Hoeft, 1988).
- Researchers in Indiana found a yield increase to starter P and K at only one site under conventional tillage (spring chisel plow) but found consistent yield increases if corn was managed under a no-tillage production system (Mengel et al., 1988).
Because starter fertilizer experiments are often conducted using N, P, and K fertilizers it is not always exactly clear which nutrient provided the yield increase; however:
- Researchers in Iowa conducted experiments in no-till high testing P soils with both P and N starter fertilizers and found that N was largely responsible for the yield increases (Bermudez and Mallarino, 2003).
- Other research supports responses to N-only starter fertilizer, most typically if cool wet soils are elevated with a chisel plow or strip tillage (Touchton and Karim, 1986).
Conclusions: It can further be concluded that if growers in the central Corn Belt states are using high rates of broadcast fertilizer (P and K) in a build-and-maintain fertilizer program, starter P and K yield responses would be even less consistent and unlikely, especially if conventional tillage practices are being utilized (Kaiser et al., 2005).
Research Results by Soil Type
Consistent grain yield responses to starter fertilizers may also be expected on soils that have low soil organic matter or soils that have coarse (sandy) soil surface textures. Many soils formed from Mississippi River alluvium that stretch from portions of central Minnesota to the Gulf of Mexico fit this description. Several studies report results by soil type:
- Researchers in Louisiana noted early P deficiencies on silt loam and sandy loam soils that have an organic matter content of less than 1 percent (Mascagni et al., 1996; Mascagni et al., 2007 ).
- These researchers found that starter N and P applications significantly increased corn grain yields in five out of 15 environments (and numerically increased yield in 12 of 15 environments) even when extractable soil P levels were high on these soils (Figure 4).
- Moreover, the average grain yield response was 12.5 bushels an acre when averaged across all years and locations, although yields were not always significant at the 0.05 probability level.
- In addition, it was concluded that the observed grain yield responses were more likely from the P in the starter fertilizer and the largest, most consistent grain yield responses were on the coarsest textured (sandiest) soils (Mascagni et al., 2007).
Figure 4. Influence of starter fertilizer on corn yield on Mississippi River alluvial sandy loam/silt soils at the NE Research Station at St. Joseph, Louisiana. Mascagni et al., 2007.
NS = Non-significant at the .05 probability level.
- Congruent research in other southern states on sandy loam soils when P and K levels were high showed consistent grain yield responses from starter fertilizers. Moreover, grain yields were significantly higher with N starter alone; however, they were slightly higher in other years when P and K starter was added (Touchton and Karim, 1986).
- Conversely, research in North Carolina showed no yield increase to P and N starter fertilizer when compared to just N starter fertilizer in sandy soils when P levels were high (Chaill et al., 2007).
Conclusions: It seems apparent from the reviewed literature that starter fertilizers of N, P and K in sandy loam and coarser-textured soils might be warranted even if P and K levels are high. However, it is impossible to tell if N, P and K are needed or just N, due to conflicting findings in these environments.
Hybrid Responses to Starter Fertilizer
Kansas State researchers studied five hybrids ranging in maturity from 103 to 113 RM, with and without starter fertilizer (N and P) in a no-tillage production system (Gordon, 1997). This Kansas study found that starter fertilizer significantly increased early season growth, N and P uptake at V6, and N and P concentration in the ear leaf. However, no hybrid by starter interaction was found (i.e., all hybrids responded similarly to starter application). The study also measured growing degree units (GDUs) to pollination. All hybrids required less heat units to begin pollination when starter fertilizer was used (Table 1). This is a key finding for dryland corn production in Kansas, where yield is often limited by late season drought stress. Furthermore, earlier pollination under these conditions can lengthen the grain filling period and increase corn grain yield potential.
Table 1. Starter fertilizer effect on grain yield and GDUs to pollination of corn hybrids. (Adapted from Gordon, 1997.)
*Significant at the 0.05 probability level.