Co-Granulated and Blended Zinc Fertilizer Comparison for Corn and Soybean

A new co-granulated formulation of monoammonium phosphate (MAP) including S and Zn could allow for more uniform nutrient distribution. A six site-year study evaluated the effects of blended phosphorus (P) sources [MAP and diammonium phosphate (DAP)] and zinc amounts (0, 2.2, and 5.6 kg Zn ha) compared to co-granulated fertilizer, MicroEssentials Sulfur-10 (MES10) (12-40-0-10S) and MicroEssentials Sulfur and Zinc (MESZ) (12-40-0-10S-1Zn), on corn and soybean response. Fertilizers were broadcast applied for corn and the carry-over effect on soybean was determined. Ear leaf P, S, and Zn concentrations at Novelty in 2013 and 2014 were within the sufficiency range regardless of treatment, even though initial soil test values were low-medium. Yields were similar to the N only control for all site-years except at Novelty in 2013, where MAP+ZnSO4 at 2.2 kg Zn ha, MAP+Super Zn at 5.5 kg Zn ha, and DAP+AMS were 540 to 570 kg/ha greater. The amount of Zn fertilizer (2.2 vs. 5.6 kg Zn ha) also showed no significant effect on yield. Applications of P or Zn generally increased their concentrations in post-harvest soil samples. Fertilizer applied for corn indicated some differences in soybean plant nutrient concentrations, but it had no effect on total plant nutrient uptake, grain yield or quality. At Novelty, soybean plant Zn concentration was greater at 5.6 kg Zn ha compared to 2.2 kg Zn ha, while Albany showed an increase in whole soybean plant Zn concentration with SuperZn compared to ZnSO4. Carry-over fertilizer from corn showed limited effects on soybean response the following year.


Introduction
Zinc (Zn) is essential to plant survival, with the average plant containing 20 ppm of the micronutrient based on dry weight (Mahler, 2004).Typical soils can contain 0.3 to 2.0 ppm (Mahler, 2004) of plant-available Zn, which is the most common deficient micronutrient in high pH soils (Graham, Asher, & Hynes, 1992).Zn is found in N metabolism pathways that can affect protein synthesis (Fageria, 2004).Deficiencies can cause interveinal chlorosis, bronzing, internode shortening, and epinasty.In severe deficiencies, the root apex can become necrotic.Although Zn is mobile in the plant, its mobility is poor and deficiency symptoms appear first in the upper, young plant leaves.Since Zn is a micronutrient, Zn toxicity is possible, but unlikely (Broadley, White, Hammond, Zelko, & Lux, 2007).Zn fertilizers are available in three major forms: Zn chelate, ZnO, and ZnSO 4 (Schulte, 2004).Water solubility greatly influences the availability and effectiveness of Zn fertilizer.In Zn chelate, commonly sold as ZnEDTA, a large organic molecule surrounds Zn and keeps it from leaching, oxidizing, and precipitating (Schulte, 2004).Zinc sulfate is the most common form, due to its low cost and greater solubility (Schulte, 2004), and has traditionally been a steadfast source in Zn fertilizer (Olsen, 1982).
Although soil may contain enough Zn to support a crop through the season, 90% of the Zn is in forms that make it unavailable (fixed, insoluble, or unexchangeable) (Broadley et al., 2007).In most soils, only 0.1 to 2 µg of Zn per gram are exchangeable (Broadley et al., 2007).Soils with large phosphate levels can cause an imbalance in a crops' physiology including a reduction in Zn uptake (Olsen, 1982).This phenomenon is known as P-induced Zn deficiency (Singh, Karamanos, & Stewart, 1986).Zinc-phosphorous interactions are well documented (Halim, can induce zinc deficiency in soils with low plant-available zinc (Robson & Pitman, 1983).In soil, P can decrease zinc's solubility (Huang, Barker, Langridge, Smith, & Graham, 2000).When P requirements are met in the plant, root growth is reduced and mycorrhizae infection less common (Amijee, Stribley, & Tinker, 1990).Deficiencies in plants could also be induced by a small concentration of Zn due to rapid growth response to P. Alternatively, large P-to-Zn ratios could cause a metabolic imbalance in cells and lead to P-induced Zn deficiencies (Singh et al., 1988).Zinc deficiency may increase in response to an expression of high-affinity phosphate transporters when P is deficient, likely because the plant utilizes resources from Zn for phosphate transporters (Huang et al., 2000).Increasing applications of both Zn fertilizer and P could help optimize yield (Schnappinger, Martens, & Hawkins, 1969), even though crops take up little Zn during the growing season.
More than 30% of the world's arable land has P-limiting yield potential (Vance, Uhde-Stone, & Allen, 2003).Phosphorus is an essential plant macronutrient that accounts for 3 to 5 g kg -1 of a plant's dry weight (Schalchtman, Reid, & Ayling, 1998).Phosphorus, a structural component in nucleic acids (DNA, RNA), transfers energy as adenosine triphosphate (ATP) and maintains cell structure with phospholipids.Though abundant in soil, P occurs primarily in a fixed form or outside of the rhizosphere and so is unavailable for plant uptake.When P is not available in adequate amounts, at least 0.2 mg L -1 in soil solution (Pierzynski, McDowell, Sims, & Sharpley, 2005), plants can become deficient.Visual signs of P deficiency include overall stunting of the plant, a purple tint from anthocyanin accumulation, and small necrotic leaf spots.Deficiency typically appears in the lower more mature leaves because P is mobile and translocates to new developing tissue (Briskin, Bloom, Taiz, & Zeiger, 2010).To overcome limited P availability in the soil and maintain soil test P levels, todays growers use P fertilizers commonly available as monoammonium phosphate (MAP) and diammmonium phosphate (DAP).
It is important to optimize sulfur (S) in crops to achieve high yields and grain quality (Tabatabai, 1984).As current environmental laws reduce sulfur emissions from power plants, crop sulfur deficiencies may become more common (Camberato, Maloney, Casteel, & Johnson, 2012).Correspondingly, the need to apply S fertilizers likely will increase in coming years.Sandy soils with small amounts of organic matter and no-till or heavy residue can increase the likelihood of sulfur deficiencies (Camberato & Casteel, 2010).Although S is considered a secondary plant nutrient (primarily because of amount needed), deficiency seriously affects plant growth and yields (Sawyer & Barker, 2012).As organic matter decomposes, it releases sulfate (SO 4 -2 ) into the soil through the process of mineralization (Hergert, 2000).For every one g kg -1 of organic matter, 2.25 to 3.36 kg ha -1 of sulfate are released annually into the soil, while 10 Mg ha -1 of corn (Zea mays L.) removes approximately 6.11 kg ha -1 of sulfur in grain alone (Schulte & Kelling, 1992).
A patented technology employed in co-granulated fertilizers combine nitrogen, P, S, and Zn into a single prill (MicroEssentials, Mosaic, Plymouth, MN).This allows for uniform distribution and possibly increased uptake of nutrients across a range of crops.MES10 (MicroEssentials Sulfur) contains MAP plus equal amounts of AMS (ammonium sulfate) and elemental sulfur (S) as 100 g kg -1 in the co-granulated material.The sulfate is immediately available for plant uptake, though the elemental sulfur must be oxidized by soil bacteria, which allows for season-long sulfur availability (Schulte & Kelling, 1992).MESZ is the same formulation as MES plus one percent ZnO.Microessential Sulfur and Zinc (MESZ) utilizes ZnO as the primary Zn source (Mosaic, 2007).Zinc oxide has the greatest percent of Zn at 72-80% compared to other Zn sources, but it is less water soluble than ZnSO 4 .
Researchers have studied the effects of co-granulated fertilizers in Iowa with corn (Sawyer & Barker, 2009), and in Arkansas with rice (Oryza sativa L.) (Slaton et al., 2010), winter wheat (Triticum aestivum L.) (Freeman, Ruffo, & Mann, 2014), and canola (Brassica napus L.) (Woolfork, Olson, Mann, & Perez, 2014); however, results have been mixed.Some studies show limited yield differences (Sawyer & Barker, 2009), while others indicate an advantage of MES and MESZ compared to a blend of the same nutrients (Slaton et al., 2010).MESZ increased yields 5.7% compared to MAP and 3.4% compared to MAP+AMS+ZnSO 4 (Freeman et al., 2014).In canola, Woolfolk et al. (2014) reported yield increases of 4% at 19 kg P 2 O 5 ha -1 and 7.1% at 56 kg P 2 O 5 ha -1 , which were related to less injury to germinating seedlings.Few studies report on the effects of the new co-granulated fertilizers on corn response in the Midwestern U.S., as well as their carry-over impact on soybean [Glycine max (L.) Merr.].The objective of this research was to evaluate corn response to MES10 and MESZ formulations to equivalent blends of DAP or MAP, S, and Zn at two amounts of Zn (2.2 and 5.6 kg Zn ha -1 ) for the impact on corn (ear leaf nutrient concentration at VT, grain yield, grain quality, and changes to soil test nutrient levels post-harvest) and soybean response (population, plant nutrient uptake, yield, and grain quality).Note.† Abbreviations: L, low; M, medium; VL, very low (Buchholz et al., 2004).

Corn
In 2011 and 2012, field research was conducted at the Greenley Memorial Research Center (39°56′N, 92°3′W) near Novelty, Missouri.In 2013 and 2014, field research was also conducted at the Hundley-Whaley Center (40°14′N, 94°20′W) near Albany, Missouri.Soil test Bray 1P at Novelty and Albany was very low (15 kg ha -1 ) to medium (36 kg ha -1 ) (Table 1).The Novelty sites were a Putnam silt loam (fine, smectitic, mesic Vertic Albaqualfs), while Albany sites were a Grundy silt loam (fine, smectitic, mesic Aquertic Argiudolls).Treatments were arranged in a randomized complete block design with five replications at Novelty and four replications at Albany.Initial (15 cm) soil samples from each replication were collected and analyzed by the University of Missouri Soil and Plant Testing Laboratory using the recommended soil test procedures for Missouri (Nathan, Stecker, & Sun, 2012).
Corn was planted in April or May, depending on yearly weather conditions using no-till (Novelty) or minimum tillage (Albany) into 3 by 9 to 15 m plots, with 76 cm row spacing.Corn followed soybean at all sites, except in 2013 at Albany, a continuous corn site.Management information is available in Table 2.
In 2013 and 2014 at Novelty, ten ear leaves were randomly selected from the middle two rows of each plot.Ear leaf samples were analyzed for P, SO 4 -S, and Zn concentrations (Bryson, Mills, Sasseville, Jones, & Barker, 2014).The two middle rows of the four-row corn plots were harvested using a plot combine (Wintersteiger Delta, Salt Lake City, UT or Massey 8, Haven, KS) measuring corn grain yields and moisture content.Corn grain yields were adjusted to 150 g kg -1 prior to analysis.Individual plot grain samples were collected during harvest and evaluated for oil, protein, and starch using a near infrared (NIR) spectroscopy (Foss Infratec, Eden Prairie, MN).

Soybean
Soybean was planted into the same plots as corn in April or May, depending on yearly weather conditions.The fields were no-till (Novelty) or minimum tillage (Albany), and plots were 3 by 9 to 15 m.In 2015, soybean was planted in July due to an extremely wet spring.Soybean was planted in 76 cm wide rows at Albany and in 19 cm rows at Novelty.Soybean followed corn in all years.Management information is available in Table 3. Whole plant tissue samples were taken in 2014 and 2015 at Novelty and Albany at R6 (Fehr & Caviness, 1971).Quadrats (0.23 m 2 ) were randomly selected from the middle two rows of each plot.The plant samples were ground, dried, and analyzed with standard extraction methods for P, S, and Zn concentrations (Bryson et al., 2014).
To determine soybean grain yields and moisture content, the two middle rows of soybean were harvested at Albany (Massey 8, Haven, KS), and a 1.5 m wide section of the plot (four, 38 cm wide rows) was harvested at Novelty (Wintersteiger Delta, Salt Lake City, UT).During harvest, individual plot grain samples were collected and evaluated for oil and protein concentration using near infrared (NIR) spectroscopy (Foss Infratec, Eden Prairie, MN).Soybean yields were adjusted to 130 g kg -1 prior to analysis.

Statistical Protocol
All corn data were analyzed with the Statistical Analysis System (SAS Institute, Cary, NC) using PROC GLIMMIX, and means were separated using Fisher's Protected LSD (P = 0.05).Corn data for Novelty in 2011 and 2012 were analyzed separately from 2013 and 2014 data due to the addition of SuperZn in the latter years.Data were combined by year and location when appropriate.Soybean data were combined over years for individual sites for all measurements.Planned contrasts were used to compare Zn sources (SuperZn vs. ZnSO 4 ) and Zn amounts (2.2 vs. 5.6 kg Zn ha -1 ).

Growing Conditions
Research at Novelty from 2011 to 2014 and at Albany in 2013 and 2014 experienced a wide range of precipitation during the growing seasons (March 31 to September 29) (Figure 1).At Novelty in 2011, corn experienced an abnormally dry spring (USDM, 2015) followed by average summer precipitation (532 mm) throughout the growing season.In 2012, the Midwestern U.S. experienced an extreme drought (USDM, 2015), with Novelty receiving only 273 mm of precipitation during the growing season.In 2013, precipitation was average at Novelty (453 mm), and above average at Albany (607 mm). jas.ccsenet.
In 2014, upstate Missouri experienced record yields due not only to cool summer temperatures (data not presented), but also to uniform distribution of precipitation, with Novelty receiving 771 mm and Albany receiving 751 mm.In 2015, precipitation at Albany and Novelty was above average, which delayed soybean planting.

Corn Response
Corn plant population was similar at all site-years (Novelty in 2011 and 2012, P = 0.86, and Novelty and Albany in 2013 and 2014, P = 0.92).Ear leaf tissue concentration at VT for P, S, and Zn were combined over the two years (Novelty in 2013 and 2014) where the measurements were collected due to an absence of a significant interaction between years.These sites had low soil test P and low-to-medium soil test Zn.Ear leaf P concentrations ranged from 2.38 to 3.13 g kg -1 (Table 4).All treatments, except the non-treated control, were similar and were within the sufficiency range for ear leaf P concentrations (2.5 to 5.0 g kg -1 ) (Jones et al., 1967;Bryson et al., 2014).The non-treated control had 2.4 g kg -1 P, which was below the plant sufficiency range (Jones et al., 1967;Bryson et al., 2014).Concentrations of ear leaf S and ear leaf P were similar.All treatments were similar, and they were up to 0.2 g kg -1 greater than the non-treated no N or no P controls.All treatments including P and N were within the ear leaf sufficiency range (1.5 to 4.0 g kg -1 ) for Zn (Jones, 1967;Bryson et al., 2014).Ear leaf S concentrations ranged from 1.6 to 2.1 g kg -1 and were greater than the no N and no P controls.Similar results for ear leaf P and S concentrations were reported in Iowa (Sawyer & Barker, 2010).There was no clear effect of Zn on P concentration, similar to other research evaluating P-Zn interactions (Keefer et al., 1972;Rehm et al., 1981).Ear leaf Zn concentrations were interesting because the N-only control treatment had the second highest Zn concentration, which indicated sufficient plant available Zn in the soil.An application of DAP+ZnSO 4 at 5.6 kg Zn ha -1 and N-only treatments had 4.13 to 9.43 mg kg -1 greater ear leaf Zn concentration than MES10 and the non-treated control.The non-treated, no N control was 5.15 to 9.43 mg kg -1 less than all other treatments for ear leaf Zn concentration, but this was probably due to N affecting Zn uptake.These data indicate no clear impact of the Zn treatments on ear leaf Zn concentration over the two years ear leaves were collected since the N-only control had ear leaf Zn concentrations similar to the Zn treatments.A corn fertilizer study in West Virginia with three amounts of Zn (0, 3.36, and 6.72 kg Zn ha -1 ) also observed no-yield response to Zn treatment (Stout & Bennett, 1983).An efficacy study of ZnO concluded that it and ZnSO 4 had similar plant nutrient recovery when incorporated in the soil; however, ZnSO 4 had a greater plant recovery than ZnO when the fertilizer was band-or surface-applied (McBeath & McLaughlin, 2014).In Michigan, a three-year study with 220 kg of fertilizer ha -1 comparing MAP and DAP observed no change in tissue P or Zn concentration and detected no yield difference between MAP and DAP (Yerokun & Christenson, 1990).In addition, P fertility did not appear to decrease Zn uptake, similar to Halim et al. (1968).
A significant two-way interaction occurred between treatments and site-years for corn grain yield; therefore, data were analyzed by individual site-years and reported separately (Table 5).In a planned comparison, contrasts comparing Zn amounts (2.2 vs 5.6 kg Zn ha -1 ), Zn sources (SuperZn vs. ZnSO 4 ), and P sources (MAP vs. DAP) showed no significant differences in yield for the four site-years (Novelty and Albany in 2014 and 2015) that were evaluated (data not presented).At Novelty in 2011, all treatments yielded 6,670 to 7,860 kg ha -1 greater than the non-treated, no-N control with yields from 9,090 to 10,280 kg ha -1 (Table 5).With the extreme drought in 2012, yields were low (1,120 to 1,770 kg ha -1 ).The non-treated control, N-only, and MESZ yielded 531 to 643 kg ha -1 greater than MAP, MAP+ZnSO 4 at 2.2 kg Zn ha -1 , MAP+ZnSO 4 at 5.6 kg Zn ha -1 , and MAP+AMS.At Novelty in 2013, MAP+SuperZn at 5.6 kg Zn ha -1 and DAP+AMS increased yields 560 to 2,850 over the non-treated control, N-only control, DAP+ZnSO 4 at 5.6 kg Zn ha -1 , and DAP+ZnSO 4 at 2.2 kg Zn ha -1 .All other treatments had similar grain yields.Grain yields at Albany in 2013 were similar among treatments (P = 0.57).In 2014, both Novelty and Albany experienced exceptionally high yields (12,700 to 16,800 kg ha -1 and 7,210 to 10,540 kg ha -1 , respectively), due to good overall precipitation (Figure 1) and low temperatures during pollination and grain fill (data not presented).At Novelty, DAP+ZnSO 4 at 2.2 kg Zn ha -1 , MAP+ZnSO 4 at 5.6 kg Zn ha -1 , MES10, and MAP+SuperZn at 5.6 kg Zn ha -1 had 763 to 4098 kg ha -1 greater yields than the non-treated control, DAP, DAP+ZnSO 4 at 5.6 kg Zn ha -1 , or DAP+SuperZn at 2.2 kg Zn ha -1 .At Albany in 2014, MAP alone yielded 1,570 to 3,300 kg ha -1 greater than the non-treated control, N-only, MES10, MESZ, DAP+SuperZn at 5.6 kg Zn ha -1 , DAP+ZnSO 4 at 5.6 kg Zn ha -1 , and MAP+AMS.Albany had medium soil test P, S, and Zn, which likely resulted in limited yield differences among treatments (Table 1).An increase in corn grain yield has been related to P uptake which has been greater than Zn fertility (Rehm et al., 1983), and there was no apparent Zn-P interaction which was similar to other research (Rehm et al., 1981).Note.† Abbreviations: AMS, ammonium sulfate; DAP, diammonium phosphate; MAP, monoammonium phosphate.‡ Data were combined over years.§ Treatments were not applied during these two years.
Grain oil, protein, and starch concentrations were observed at Novelty (2011Novelty ( , 2013Novelty ( , and 2014) ) and Albany (2013 and2014), but none of the treatments affected grain oil concentration at any site-year [(Novelty in 2011 and 2012, P = 0.41) (Novelty and Albany in 2013 and 2014, P = 0.16)] (data not presented).Grain protein at Novelty in 2013 and 2014 as well as Albany in 2013 and 2014 had no treatment-by-year interaction, so data were combined over years (Table 6).At Novelty in 2011, protein concentration ranged from 70 to 96 g kg -1 .All fertilizer treatments were similar, but they were 19 to 26 g kg -1 greater than the no N, non-treated control.Novelty in 2012 showed no significant difference (P = 0.11) among treatments, which likely was due to extreme drought (data not presented).At Novelty and Albany in 2013 and 2014, protein concentration with MAP+AMS was significantly greater than MAP+SuperZn at 5.6 kg Zn ha -1 and the non-treated control by 3 and 15 g kg -1 , respectively.All other fertilized treatments had similar protein concentrations that ranged from 83 to 85 mg kg -1 .At Albany in 2013 and 2014, protein concentrations ranged from 73 to 83 g kg -1 .DAP+AMS, MAP+ZnSO 4 at 5.6 kg Zn ha -1 , and DAP+SuperZn at 5.6 kg Zn ha -1 had 6 to 11 g kg -1 greater protein concentration than the non-treated control, N-only, MAP, MES10, and MAP+ZnSO 4 at 2.2 kg Zn ha -1 .At Novelty in 2011, the non-treated control had 64 to 170 g kg -1 higher starch concentration than all other treatments (Table 7).MAP had 68 to 124 g kg -1 greater starch concentration than all other fertilizer treatments.Novelty in 2012 showed no differences among treatments (P = 0.87).At Novelty in 2013 and 2014, the non-treated control was 52 to 96 g kg -1 greater than all treatments except DAP+AMS.At Albany in 2013 and 2014, DAP, DAP+ZnSO 4 at 5.6 kg Zn ha -1 , MAP+ZnSO 4 at 2.2 kg Zn ha -1 , and DAP+SuperZn at 2.2 kg Zn ha -1 had 59 to 100 g kg -1 greater grain starch concentration than MAP+SuperZn at 2.2 kg Zn ha -1 , DAP+SuperZn at 5.6 kg Zn ha -1 , DAP+SuperZn at 2.2 kg Zn ha -1 .At Albany in 2013 and 2014, all treatments had similar starch concentrations (P = 0.17).
Soil test S and Zn had a significant site-year-by-treatment interaction, but due to similar soil series, data were combined over years for individual sites and analyzed.Soil test Zn ranged from 0.56 to 2.44 mg ha -1 and 0.71 to 1.56 mg ha -1 at Novelty and Albany, respectively.All treatments had at least medium soil test Zn at the end of the growing season (Buchholz et al., 2004).When Zn was applied at Novelty in 2013 and 2014, soil test Zn generally increased compared to fertilizer treatments that had no Zn.DAP+SuperZn at 5.6 kg Zn ha -1 and MAP+ZnSO 4 at 5.6 kg Zn ha -1 had significantly greater soil test Zn than all other treatments, while all other treatments with P, S, or Zn, were similar.At Albany, DAP+ZnSO 4 at 2.2 kg Zn ha -1 and MAP+ZnSO 4 at 5.6 kg Zn ha -1 , and MAP had 1.1 to 1.5 mg kg -1 greater soil test Zn than DAP+AMS, MAP+AMS, N-only, and the non-treated control, but all other treatments were similar.This indicates that even though there was no crop yield response to Zn, soil buildup occurred.--kg ha -1 ---------plants ha -1 ---------------kg ha -1 -----------------------------g kg -1 ---------------------- Note.† Population and yield data were determined for all site-years.Grain oil and protein data were determined at all site-years except Albany in 2014.Data were combined over site-years unless denoted otherwise.
Soil test S ranged from 4.1 to 6.6 mg kg -1 and 4.2 to 6.2 mg kg -1 at Novelty and Albany, respectively.All treatments had medium soil test S.At Novelty, all treatments with S or Zn had similar soil test S levels (Buchholz et al., 2004).MESZ and MES10 had 0.98 to 2.56 higher soil test S amounts than the non-treated control, N-only, DAP, and MAP.At Albany, MAP+AMS had a 1.07 to 2.01 mg kg -1 greater soil test S concentration than DAP+SuperZn at 5.6 kg Zn ha -1 , MAP+ZnSO 4 at 2.2 kg Zn ha -1 , DAP+ZnSO 4 at 2.2 kg Zn ha -1 , DAP, and N-only.Treatments that included AMS, MES10, and MESZ had similar soil test S concentrations.

Soybean Response Following Corn
Soybean plant population ranged from 303,000 to 340,200 plants ha -1 , but was non-significant (P = 0.52) between treatments (Table 9).At Novelty and Albany in 2014 and 2015, whole-plant samples taken before physiological maturity at R6 (Fehr & Caviness, 1971) were analyzed for P, S, and Zn concentration.At Novelty in 2014 and 2015, no differences were seen in plant P (P = 0.69) or S (P = 0.26) concentration (Table 10).At Albany in 2015, no significance differences appeared between plant P (P = 0.64), S (P = 0.66), or Zn (P = 0.98) concentration; however, at Albany in 2014, P, S, and Zn concentrations were significantly different.At Albany in 2014, plant P concentration ranged from 2.48 to 3.81 g kg -1 .Plant P concentration in the DAP+AMS treatment was 0.57 to 1.33 g kg -1 greater than all treatments.The N-only control had a plant Zn concentration similar to 7 of the 16 treatments, indicating there may be no strong effect regarding application of P for soybeans between treatments applied for corn and plant P concentrations observed in soybean the following year.A 14-site study in Iowa showed increased P uptake at eight sites (Borges & Mallarino, 2003).
At Albany in 2014, whole-plant S concentration ranged from 1.95 to 2.99 g kg -1 (Table 10).Similar to plant P concentration, DAP+AMS had the greatest plant S concentration, which was 0.33 to 1 g kg -1 greater than all treatments except MAP+SuperZn at 5.6 kg Zn ha -1 and DAP+SuperZn at 5.6 kg Zn ha -1 .Interestingly, treatments including SuperZn generally had a greater plant S concentration than treatments including ZnSO 4 .Again, this could point to the lack of a good relationship between fertilizer treatments and plant S concentrations.Similarly, when S fertilizer was applied to wheat in a wheat-soybean rotation, no significant differences were reported in soybean S concentrations (Singh et al., 2014).
Plant Zn concentration was significantly affected at both locations in 2014 and Novelty in 2015 (Table 10).At Albany in 2014, plant Zn concentrations ranged from 24.2 to 35.6 mg kg -1 .Similar to both plant P and S concentration data, DAP+AMS had the highest plant Zn concentration at 35.6 mg kg -1 , which was 5.0 to 11.4 mg kg -1 greater than all treatments except DAP+SuperZn at 5.6 kg Zn ha -1 and MAP+SuperZn at 2.2 or 5.6 kg Zn ha -1 .In a planned contrast comparing Zn rate (2.2 vs. 5.6 kg Zn ha -1 ) and Zn source (SuperZn vs. ZnSO 4 ), SuperZn had significantly higher plant Zn concentration than ZnSO 4 (P = 0.0005), while Zn rate showed no significant difference (P = 0.12).At Novelty in 2014 and 2015, plant Zn concentration ranged from 26.1 to 34.7 mg kg -1 .MAP+SuperZn at 5.6 kg Zn ha -1 increased plant Zn concentration by 4.9 to 10.3 mg kg -1 over all treatments except DAP+ZnSO 4 at 5.6 kg Zn ha -1 .In a planned contrast comparing Zn rate (2.2 vs 5.6 kg Zn ha -1 ) and Zn source (SuperZn vs ZnSO 4 ), Zn at 5.6 kg Zn ha -1 increased plant Zn concentration compared to 2.2 kg Zn ha -1 (P = 0.0008), while Zn source was not significant (P = 0.72).These results showed completely different responses at Novelty compared to Albany.Nutrient concentration and total plant tissue weights were used to calculate total plant uptake of P, S, and Zn (Table 11).Although significant differences were observed in plant nutrient concentrations, all treatments were similar when total plant uptake was calculated [P (P = 0.52), S (P = 0.49), and Zn (P = 0.60)].In 2012 and 2013, grain yields ranged from 2,380 to 2,490 kg ha -1 , and all treatments yielded similarly (P = 0.85) (Table 9).Seed oil and protein content were measured to determine any impact of treatments on seed quality.Seed oil ranged from 191 to 197 g kg -1 , with no difference between treatments (P = 0.42).Protein concentration ranged from 352 to 360 g kg -1 , but also showed no effects of the treatments (P = 0.46).In 2014 and 2015, soybean population, yield, oil, and protein combined over years and locations (Novelty and Albany).Soybean plant population  ranged from 293,300 to 336,800 plants ha -1 and showed no difference among treatments (P = 0.15).Similarly, yields (2,900 to 3,200 kg ha -1 ) showed no differences among treatments (P = 0.16) (Table 9).Grain quality (oil, protein) was also similar among treatments (P = 0.37, P = 0.46, respectively).Between treatments, seed oil concentration had a small range, 180 to 190 g kg -1 , and protein concentration had a narrower range, 346 to 349 g kg -1 .
Fertilizer applications to corn in a corn-soybean rotation had inconsistent effects on soybean yield and seed quality.Anthony et al. (2012) and Buah, Polito, and Killorn (2000) reported no difference in yield between 0 and 56 kg P ha -1 .However, others have shown increased yields, but at low soil test P levels (Borges & Mallarino, 2000, 2003).An Iowa study at over 112 locations showed positive yield effects from P fertilizer at only 20 sites (Haq & Mallarino, 2005).Applications of S fertilizer have also had mixed results.Divito, Echeverria, Andrade, and Sadras (2015) reported increased yields with S application, while Singh et al. (2014) reported no response to S fertilizer.

Conclusion
Variation in precipitation over site-years strongly affected corn grain yields.Ear leaf P tissue concentration at VT showed fertilized treatments within the sufficiency range, with no significant difference among treatments.Ear leaf S tissue concentration at VT showed no significant differences, except for the non-treated control.All fertilized treatments were within the ear leaf S sufficiency range.All treatments were similar for ear leaf Zn concentration at VT, except for the non-treated control, which was significantly lower than all other treatments and for MES10, which was significantly lower than N-only and DAP+ZnSO 4 at 5.6 kg Zn ha -1 .Yields showed no significant differences at Novelty in 2013, and all treatments were similar at Novelty in 2011.In 2012, because of a severe drought, yields in the non-treated control were the greatest.At Novelty in 2014 and Albany in 2013 and 2014, adding S and/or Zn had no effect on yield.The rate of Zn fertilizer (2.2 vs 5.6 kg Zn ha -1 ) also showed no significant effect on yield.When P was determined post-harvest, soil samples reflected the application of P fertilizer.Generally, when Zn was applied, soil test Zn increased.At Novelty, MES10 and MESZ had the greatest increase in soil test S, while at Albany MAP+AMS had the greatest amount of soil test S. Carry-over fertilizer from corn experiments showed differences in plant nutrient concentrations, but this had no effect on total plant nutrient (P, S, or Zn) uptake, grain yield or quality.However, at Novelty plant Zn concentration was increased with 5.6 kg Zn ha -1 compared to 2.2 kg Zn ha -1 , while Albany showed an increase in soybean Zn concentration with SuperZn when compared to ZnSO 4 .This indicates that micro-nutrient uptake was affected by Zn rate and source, depending on the soil type.

Figure
Figure 1.P Bars pr

Table 4 .
Corn ear SO 4 -S concentration for Zn treatments at Novelty from 2013-2014.Data were combined over years.All P amounts were 80 kg P 2 O 5 ha -1

Table 8 .
Soil test P, Zn, and SO 4 -S after corn harvest at Novelty and Albany(2013)(2014).Phosphorus was applied at 90 kg P 2 O 5 ha -1 for all treatments including P

Table 10 .
Soybean whole plant P, S, and Zn concentrations as affected by Zn treatments at Albany and Novelty in 2014-2015 Note.