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Cornell Univ., Ithaca, NY 14853
* Corresponding author (qmk2{at}cornell.edu).
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ABSTRACT |
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 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: CNAL, Cornell Nutrient Analysis Laboratory • CP, crude protein • DM, dry matter • DMI, dry matter intake • dNDF, digestibility of neutral detergent fiber • FLG, forage-legume-grass • FYC, first year corn • LOI, loss-on-ignition • NDF, neutral detergent fiber • NY, New York • OM, organic matter • PSNT, pre-sidedress nitrate test • SBM, soybean meal • SP, soluble protein • TMR, total mixed ration • UAN, urea ammonium nitrate
Cornell Univ., Ithaca, NY 14853
* Corresponding author (qmk2{at}cornell.edu).
Received for publication February 23, 2007.
Decomposition of forage legume-grass (FLG) sods after turnover will supply N to the next corn (Zea mays L.) crop. For optimum economic grain production typically a starter N application is sufficient. However, the impact of eliminating sidedress N on yield and quality of silage corn in the year after sod turnover (FYC) is not well documented and little is known about the effects of timing of sod turnover (fall or spring) or sod composition (percentage legume) on N fertilizer needs of FYC. In 2005 and 2006, 13 on-farm and three research station N trials were conducted throughout New York (NY) to determine (i) N needs for optimum yield and quality of FYC and (ii) the impact of FLG composition and timing of sod kill on the likeliness of an economic N fertilizer response. On-farm trials included four sidedress N rates (0, 56, 112, and 168 kg N ha–1) with a small, banded starter application (34 kg N ha–1 maximum). The three research sites also contained a no starter control. Eliminating the starter resulted in significantly lower yields while sidedress N did not increase yield at any of the 16 sites. Nitrogen application increased crude protein (CP) levels but did not affect other silage quality parameters or estimated milk production. The increase in CP came at great economic (fertilizer) and environmental (low apparent N recovery) costs. We conclude a small starter application is sufficient for optimum yield and quality of FYC regardless of timing of sod turnover or its composition.
Abbreviations: CNAL, Cornell Nutrient Analysis Laboratory • CP, crude protein • DM, dry matter • DMI, dry matter intake • dNDF, digestibility of neutral detergent fiber • FLG, forage-legume-grass • FYC, first year corn • LOI, loss-on-ignition • NDF, neutral detergent fiber • NY, New York • OM, organic matter • PSNT, pre-sidedress nitrate test • SBM, soybean meal • SP, soluble protein • TMR, total mixed ration • UAN, urea ammonium nitrate
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INTRODUCTION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Many studies have looked at the rotational effects of and N credits from legumes on the dry matter (DM) production of the subsequent corn grain crop; these include studies with corn after alfalfa (Bundy and Andraski, 1993; Fox and Piekielek, 1988; Baldock and Musgrave, 1980; Morris et al., 1993; Schmitt and Randall (1994); Schmitt et al., 1996; El-Hout and Blackmer, 1990; Levin et al., 1987), birdsfoot trefoil (Lotus corniculatus L.) (Fox and Piekielek, 1988; Schmid et al., 1959), and red clover (Trifolium pretense L.) (Fox and Piekielek, 1988; Peterson and Varvel, 1989). In Wisconsin, Bundy and Andraski (1993) concluded, based on data from 24 sites, there was no need for additional N fertilizer for FYC after alfalfa. In Pennsylvania, Fox and Piekielek (1988) obtained the same results for FYC after alfalfa, birdsfoot trefoil, and red clover. Morris et al. (1993) found 6 responsive sites out of 29 first year corn sites after alfalfa in Iowa with an optimum N rate of 28 kg N ha–1 for the responsive sites consistent with a small starter N application. Schmitt and Randall (1994) reported that only one out of five sites in Minnesota showed a response to N fertilizer with an optimum N rate of 47 kg N ha–1. These Wisconsin, Pennsylvania, Iowa, and Minnesota studies suggest only 1 of 61 FYC grain trials required additional N beyond a small amount of starter N to optimize DM yield. However, information on silage corn N needs in the year after sod turnover is scarce.
Nitrogen release can vary depending on sod composition. For example, in the study by Fox and Piekielek (1988) N fertilizer recommendations could be reduced by 134, 100, and 100 kg ha–1 for grain corn after alfalfa, birdsfoot trefoil, and red clover, respectively, showing greater N release from the alfalfa stand. However, the biggest differences are generally observed when legume N credits are compared to grass N credits. In a long-term study on a Typic Hapludults soil in the Southern Piedmont Region, Adams et al. (1970) reported that, when no additional N was applied, grain yields for corn after alfalfa were higher than for corn after tall fescue (Festuca arundinacea Schreb.) suggesting greater N release from the alfalfa than the fescue stand.
In the northeastern U.S. forage sods are rarely pure stands; in 2005 estimates for NY indicate that more than 80% of the alfalfa grown is grown with a grass companion crop (Cherney et al., 2006). Current NY guidelines for N credits from sods suggest an estimated total N pool of 168, 224, 280, 336 kg ha–1 for sods consisting of 0, 1 to 25, 26 to 50, and >50% legume, respectively. Nitrogen availability in the year after sod turnover is expected to be 93, 123, 155, 185 kg ha–1 when the sod consists of 0, 10 to 25, 26 to 50, and >50% legume, respectively (Ketterings et al., 2003). These guidelines do not specify the aboveground biomass of the stand and field studies are needed to validate these N release estimates (N credits) for higher yielding modern corn silage hybrids and current management practices.
Current NY guidelines do not quantify timing of sod turnover as a factor in determining N credits from the sods either although N-leaching guidelines suggest that sod turnover should not occur until the soil temperature is below 7°C at a depth of 10 cm (generally early October in NY) (Ketterings et al., 2003). Additional research is needed to better quantify the probability of a corn yield response to additional N in the first year after sod turnover in late fall vs. early spring under NY growing conditions and for grass, alfalfa, and alfalfa–grass mixtures.
To date most studies have focused on grain corn. When growing corn for silage, DM yield and forage quality parameters such as CP, neutral detergent fiber (NDF), and digestibility of NDF (dNDF), need to be studied. Optimum N rates for DM yield and for quality might not be identical. For example, Cox et al. (1993) reported that in a 2-yr field study in central NY maximum economic DM yields for corn occurred at a N rate of 150 kg ha–1 while silage quality (expressed as NDF and in-vitro DM digestibility) increased linearly as N rate increased from 0 to 200 kg N ha–1. This study included first and second year corn following buckwheat [Fagopyrum sagittatum Gilib. (esculentum)] on a Honeoye silt loam soil (fine-loamy, mixed, active, mesic Glossic Hapludalfs). In contrast, O'Leary and Rehm (1990) reported that in southeastern and central Minnesota, on silt loam and sandy loam soils, corn DM yield increased linearly (three sites) or curvilinearly (five sites) with inconsistent corn silage quality responses with N applications of 0, 84, 168, and 252 kg N ha–1 and optimum N rates exceeding the highest N rate at four of the eight sites.
Given the humid climate in the northeastern United States, excess N will most likely result in N losses with potentially significant environmental and economic implications (Morris et al., 1993; Bundy and Andraski, 1993), and with the increase in the price of N fertilizer there is renewed interest in optimizing N use for crop production. The objectives of this study were to determine (i) the effects of starter and sidedress N applications on both DM yield and forage quality of FYC and (ii) the effect of sod composition and timing of sod kill on the likelihood of an economic response to N application.
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MATERIALS AND METHODS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Plot Design
Most trials (13 of 16) had four sidedress N treatments: 0, 56, 112, and 168 kg N ha–1. The remaining three (research station) trials also contained a no starter control resulting in five treatments. Trials were replicated four times (complete block design). Each experimental plot was four rows (3 m) wide and 18 m long with the exception of two on-farm sites, one of which was six rows (4.5 m) wide while the other was eight rows (6 m) wide.
Soil Sampling and Fertility Management
Soil samples were taken (eight per plot, 0–20 cm depth) at each of the 16 sites. Samples were kept cool while sampling in the field, oven-dried ( <50°C) for at least 48 h on arrival at the laboratory, and crushed to pass 2 mm before storage for later analysis following standard soil preparation procedures at Cornell University (Greweling and Peech, 1965). Soils were analyzed for pHwater, organic matter by loss-on-ignition (Storer, 1984), and Morgan extractable P, K, Ca, and Mg (Morgan, 1941). All soil analyses were performed at the Cornell Nutrient Analysis Laboratory (CNAL) using methods described in Wolf and Beegle (1995). Soil pH was measured in a 1:1 (w:v) water extract. Percent organic matter was calculated from loss-on-ignition (LOI) using the following formula: % organic matter (OM) = (% LOI x 0.7) – 0.23 (Renuka Rao, personal communication, 2007). For the Morgan extraction, samples were shaken in a 1:5 soil/solution (v/v) ratio for 15 min and filtered through a Whatman No. 2 filter paper. Morgan extractable PO4–P was measured colorimetrically (Murphy and Riley, 1962) using an Alpkem automated rapid flow analyzer (RFA/2–320) (OI Corp., College Station, TX). Potassium, Ca, and Mg were analyzed using a JY70 Type II ICP–AES (Jobin Yvon, Edison, NJ).
Initial soil test results (Table 2 ) showed that four sites were low or medium in P (below the agronomic optimum). Sites low or medium in P carry recommendations for additional P through either manure or fertilizer while the chance of a response to P in the starter band for soils high or very high in P is minimal (Ketterings et al., 2005). Since no manure was applied to any of the sites starter fertilizer applications were used to supply the P at these sites. The research station sites in Essex County received an additional 90 kg ha–1 of K2O (pre-plant incorporated). No other nutrients were limiting production at any of these sites and pH levels were optimal for corn production.
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At the time of harvest, soil samples (eight per plot) were taken between sidedressed rows to determine end-of-season soil nitrate levels. The samples were also taken at a 0 to 30 cm depth, reflecting current NY nitrate sampling guidelines. This nitrate test indicates how much N is left in the soil profile at the end of the growing season. Given the humid climate in the northeastern United States there is a high likelihood that any nitrate remaining in the soil at the end of the growing season will be lost before the subsequent growing season and thus, the end-of-season soil nitrate test is an indicator of post-harvest N loss potential. Samples were kept cool while in the field, oven-dried ( <50°C) for at least 48 h on arrival at the laboratory, and crushed to pass 2 mm before being analyzed for Morgan extractable nitrate (Morgan, 1941). Nitrate analysis was performed colorimetrically using an Alpkem automated rapid flow analyzer (RFA/2–320) (OI Corp., College Station, TX).
Harvest, Silage Quality Analyses, and the End-of-Season Stalk Nitrate Test
Harvest was initiated when the whole-plant moisture content was between 600 and 700 mg kg–1. A minimum of two rows of 12 m length were harvested per plot. All plants in the harvested area were counted to determine stand density at harvest. A five plant subsample from each plot was chopped in the field for moisture content and forage quality analyses using a Model #120312 Mighty Mac, a gas-powered chipper-shredder (Mackissic Inc., Parker Ford, PA). Samples were well-mixed, subsampled to fill a 3.78 L plastic bag, sealed, and kept in a cooler before drying in a 60°C forced-air oven for a minimum of 48 h.
Forage subsamples were analyzed at Cumberland Valley Analytical Services, Inc., Hagerstown, MD, for moisture content (Association of Official Analytical Chemists, 1990b), CP (Association of Official Analytical Chemists, 1990d), soluble protein (SP) (Krishnamoorthy et al., 1982), NDF, and 48 h digestibility of NDF (dNDF) (Goering and Van Soest, 1970), lignin (Goering and Van Soest, 1970), starch (Holm et al., 1986), ash (Association of Official Analytical Chemists, 1990c), and fat (Association of Official Analytical Chemists, 1990a). Milk2006, a model developed at the University of Wisconsin, was used to estimate milk yields (Shaver, 2006). Milk per Mg is an assessment of overall quality integrating CP, NDF, dNDF, starch, ash, and fat.
A 20-cm portion of stalk (between 15 and 35 cm above the ground) was collected from an additional five plants in the harvest area as described in Binford et al. (1990). These samples were dried at 60°C in a forced air oven for a minimum of 48 h, ground to pass a 425 µm screen, and analyzed for extractable nitrate using a 0.025 M aluminum sulfate [Al2(SO4)3] solution, an extraction ratio of 1:100 (w/v) and a shaking time of 15 min. Extractable nitrate (NO3) was determined using a VWR SympHony nitrate ion electrode (Catalog #14002–818, VWR Corp., West Chester, PA) following Miller (1998).
Statistical Analysis
Data were analyzed using PROC MIXED of the Statistical Analysis System (SAS Institute, Cary, NC). Individual site assessments were performed with N treatment as the fixed effect and block as the random effect. The three sites that contained a no starter treatment were analyzed together with N treatment as the fixed effect and location x block as the random effect. Overall analysis was performed on all 16 sites (the 13 on-farm and three research station trials, excluding the plots containing the no starter treatment) with N treatment as the fixed effect and location x block as the random effect. Mean separations were done using the LSMEANS procedure with TUKEY adjustment at P 
0.05.
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RESULTS AND DISCUSSION |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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In our NY study, sidedress N did not result in a yield increase in any of the sites, independent of sod composition, timing of sod kill, and type of tillage. Average DM yields at these sites were 17.0, 17.4, 17.6, and 17.6 Mg ha–1 for sidedress rates of 0, 56, 112, and 168 kg N ha–1, respectively (Table 3). These results are consistent with both the current N recommendation system for FYC after FLG sods in NY (Ketterings et al., 2003) and the corn grain studies by Bundy and Andraski (1993), Fox and Piekielek (1988), Morris et al. (1993), and Schmitt and Randall (1994), expanding the number of nonresponsive sites in these five studies to 70 out of 77 sites while the optimum N rate for the six responsive sites in Iowa was 28 kg N ha–1, consistent with a small starter N application.
Forage Quality
Although N uptake at the 16 sites varied greatly (Table 4
), N sidedressing did not impact NDF, dNDF, lignin, and starch at any of the sites (Table 3); however, there were significant increases in both CP and SP. This is consistent with findings by Sheaffer et al. (2006) who reported that N fertilization increased forage CP concentrations but had little effect on other forage quality components. Cox et al. (1993) and O'Leary and Rehm (1990) also reported that N fertilization increased whole plant CP concentrations; however, these studies showed less consistent results in terms of other silage quality parameters.
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An increase in CP could result in a decrease in protein purchases from off-farm sources. Total mixed ration (TMR) is currently a commonly recognized method for feeding a dairy herd. Cherney et al. (2004) indicate that a TMR which contains corn silage as approximately 58% of DM is typically found in the Northeast, while CP is approximately 19% of DM in the TMR. If we assume that a typical dry matter intake (DMI) is approximately 22 kg d–1 (Cherney et al., 2004) the DMI of corn silage and CP would be 12.8 and 4.2 kg d–1, respectively. Given a CP content of 71.4 g kg–1 (starter only treatment in our study), the CP intake from corn silage would amount to 0.9 kg d–1 or approximately 22% of the total CP in the TMR. The application of 168 kg N ha–1 sidedress N increased the CP content of the silage to 78.1 g kg–1; this would increase the CP content from corn silage to 1.0 kg d–1 or approximately 24% of the total CP in the TMR. Therefore, the increase in corn silage CP of 6.7 g kg–1 would account for 2% of CP needed in the daily TMR.
Given an average DM yield of 17.4 Mg ha–1, a 6.7 g kg–1 increase in CP equates to an additional 117 kg CP ha–1. A common fertilizer used for sidedressing is urea ammonium nitrate (UAN). If we assume a fertilizer cost of U.S.$287 Mg–1 UAN (32%N) or U.S.$896 Mg–1 of actual N, the 117 kg ha–1 increase in CP upon addition of 168 kg N ha–1 cost U.S.$150 ha–1 in fertilizer expenses alone. If we assume that soybean meal (SBM) with 48% CP is currently priced at U.S.$0.63 kg–1 (Ishler, 2007) the purchase of 117 kg CP ha–1 from SBM would equate to a cost of U.S.$73 ha–1. The increase in CP in the silage is therefore not large enough to be of economic value; it would be cheaper to buy the SBM. In addition, the application of 168 kg N ha–1 resulted, across all sites, in an increase in total N uptake of only 18.2 kg ha–1 (data not shown), reflecting an extremely low apparent N recovery of only 15%. Thus, the increase in CP with N fertilization greatly increased the potential for N loss to the environment.
Pre-sidedress and End-of-Season Soil and Stalk Nitrate Tests
The lack of yield response to N indicates that corn plants had sufficient N for optimum growth providing that a small starter application was applied. Yet, the PSNT results and NY interpretations suggested additional N was needed for 6 to 9 of the 16 sites (Table 4). Interpretation of the PSNT in NY does not differentiate between FYC or second year and greater year corn. Work performed in Iowa suggests that critical values are lower for FYC and a critical value of 14 mg kg–1 nitrate N was proposed to distinguish between soils that should and should not be fertilized with additional N (Morris et al., 1993). However, even when this interpretation is used for our NY study, additional N would have been called for at 5 of the 16 sites. These results show the PSNT is not a reliable tool for predicting a yield response to sidedress N for FYC. Furthermore, the lack of a response to additional N shows a PSNT is not needed to guide N management for FYC.
For several sites, soil nitrate levels at harvest were extremely low, most likely reflecting N leaching conditions during the latter part of the growing season. At other sites the end-of-season soil nitrate levels exceeded 10 mg kg–1 suggesting the potential for N losses over the fall, winter, and early spring (Ketterings et al., 2003). Nitrogen sidedressing increased soil nitrate levels at harvest at only 2 of the 16 sites. In relatively wet growing seasons such as 2005 and 2006 it is possible that nitrate moved below the 30-cm sampling depth but any remaining nitrate is not likely to remain in the soil profile in the humid Northeast (Morris et al., 1993; Bundy and Andraski, 1993).
Earlier work on stalk nitrate test interpretations for grain corn suggested an optimum range between 700 and 2,000 mg NO3–N kg–1 (e.g., Binford et al., 1992) and this range is commonly used in the northeastern United States (e.g., Agricultural Analytical Services Laboratory, 2007; Soil Nutrient Analysis Laboratory, 2007). Hooker and Morris (1999) developed interpretations for silage corn (earlier sampling than for grain corn) and reported a critical value of 500 mg NO3–N kg–1 while Fox et al. (2001) reported a 93% accuracy for a critical level of 250 mg NO3–N for silage corn. If we assume the optimum range of 250 to 2,000 mg NO3–N for silage corn as suggested by Fox et al. (2001), the stalk nitrate data from starter N only treatments in our NY study suggested excessive N for eight sites, optimum N supply for five sites, and N deficiency for three (Table 4). Since there were no yield responses at any of the sites, these results suggest the critical values for the end-of-season stalk nitrate test for NY might need to be lower than levels currently suggested for use in the Northeast.
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CONCLUSIONS |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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NOTES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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REFERENCES |
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TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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