Effect of Source and Rate of Nitrogen and Sulfur Fertilizer on Yield, Quality, and Mineral Composition of Stockpiled Tall Fescue

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Jeremy W. Singer, USDA-ARS, National Soil Tilth Laboratory, Ames, IA; Kenneth J. Moore, Roger L. Hintz, and Patricia K. Patrick, Department of Agronomy, Iowa State University, Ames, IA; and Paul Summer, Ajinomoto USA Inc., Eddyville, IA

Abstract

Field research was conducted for 2 years to determine the effects of N and S sources and rates on stockpiled tall fescue (Festuca arundinacea Schreb.) forage yield, quality, and mineral concentrations at different autumn harvest dates and a forage harvest the following spring. High lysine fertilizer (HLF), which contains approximately 6% total N and SO₄, produced dry matter (DM) yields similar to NH₄NO₃ when combining the autumn stockpiled yield with a harvest the following spring. However, NH₄NO₃ produced more stockpiled forage than HLF in 1 of 2 years. Combining autumn and spring harvests, each pound of fertilizer N increased forage yield by 24.8 to 27.5 lb DM during the 2-year study period. Adding N increased forage quality, regardless of the N source. But adding S did not improve forage quality or DM yield. Tall fescue harvested in late October or early November compared to early October had greater DM yield in 1 of 2 years (9%) and lower crude protein and in vitro dry matter digestibility (IVDMD) both years. Growers deciding between N sources should base their decisions on forage supply and cost because cumulative performance of tall fescue using both N sources was similar.

Introduction

Late summer growth of tall fescue is often allowed to accumulate for autumn and early-winter grazing in the Midwest. Application of fertilizer N increases DM yield and improves forage quality of stockpiled tall fescue (6,7,12,14). High lysine fertilizer is a manufacturing byproduct of crystallized lysine production that contains approximately 6% total N and SO₄. About 20% of the total N is in organic forms, which is not immediately available for plant uptake and requires microbial breakdown and conversion to plant available forms. This organic nitrogen is less susceptible to leaching and should be released for plant use over a longer period compared to commercial fertilizers such as NH₄NO₃ and urea.

Generally, fertilization with S has not increased forage yields, probably because of indirect S inputs from rainfall and soil S content. Buchholz and Whitney (4) reported that crop response to sulfur was likely in Kansas on soils with less than 2.6% organic matter. Sweeney and Moyer (17) reported that the addition of S fertilizer up to 30 lb/acre had little effect on spring tall fescue DM yields. Nevertheless, S has been reported to decrease lignification and improve fiber digestibility of some forages, but the results have been inconsistent and have varied with forage species (11).

Sulfur fertilization decreased lignin concentration and increased fiber digestibility in sorghum (1). However, Sweeney and Moyer (17) reported that applying S at 15 or 30 lb/acre did not affect concentrations of neutral detergent fiber (NDF) or IVDMD in tall fescue when harvested in the spring as hay in Kansas. Because HLF contains a significant quantity of sulfur, it is possible that fertilization of tall fescue with HLF may have a positive impact on stockpiled forage quality. The objectives of this experiment were to evaluate the effects of HLF fertilizer on yield, quality, and mineral composition of stockpiled tall fescue at two autumn harvest dates compared to inorganic N and S fertilizer sources and a forage yield the following spring.

Measuring Fertilizer Source & Rate Effects on Stockpiled Tall Fescue

The experiment was conducted near Ames, IA (42°00’N, 93°50’W) on plots that were established in April of 2002 using 'Kentucky 31' tall fescue on Clarion loam soil (fine-loamy, mixed, mesic, typic Hapladoll). Soil pH was 6.4 to 6.5 and organic matter was 3.6 to 5.9% during the study period. The tall fescue had last been harvested on 18 July 2003 and 28 June 2004. In early August both years, 2,4-D (2,4-Dichlorophenoxyacetic Acid) was applied to control broadleaf weeds. Treatments consisted of a no fertilizer control, HLF applied at rates of 320, 640, and 1280 lb/acre, NH₄NO₃ applied at rates of 68, 136, and 272 lb/acre, and CaSO₄ applied at rates of 118, 235, and 471 lb/acre. Actual fertilizer analysis of HLF averaged 6.2% S and 7.1% N. Application rates of NH₄NO₃ and CaSO₄ were adjusted to provide equivalent rates of elemental N and S as HLF, which were 23, 46, and 91 lb of N per acre and 20, 40, and 80 lb of S per acre. Treatments were applied 14 August 2003 and 17 August 2004 to different plots each year. Ammonium nitrate and CaSO₄ were applied with a Gandy granular fertilizer spreader (Gandy Co., Owatonna, MN). High lysine fertilizer was applied using a boom sprayer with 20-inch nozzle spacing operated at 30 psi. Following application, residual HLF was rinsed from foliage by application of 40 gal of water per plot. Plot size was 20 × 20 ft.

Plots were harvested on 1 and 29 October 2003 and 4 October and 3 November 2004 to determine yield and subsampled for laboratory analyses. Another harvest was made on 19 May 2004 and 31 May 2005 of the year following fertilization to determine the residual treatment effects on forage yield. All spring harvests were made on the same plots that were harvested the previous autumn. Plots were harvested with a sickle-bar plot harvester with a 5-ft effective cutting width at a 2-inch height. Dry matter was determined on subsamples after drying in a forced-air dryer at 140°F for 48 h. Samples were prepared for laboratory analysis by grinding to pass through a 0.04-inch mesh screen using a UDY cyclone mill (UDY Manufacturing, Fort Collins, CO).

All samples were analyzed to determine IVDMD, and concentrations of N, fiber, and mineral constituents. The NC-64 direct acidification procedure was used to determine IVDMD (9). Neutral detergent fiber was determined using the ANKOM 200 Fiber Analyzer (ANKOM Technology Corp., Fairport, NY) as described by Vogel et al. (19). Total N was determined by dry combustion (CHN- 2000, LECO Corp., St. Joseph, MI) using a modification of the Dumas Method, and multiplied by a factor of 6.25 to calculate crude protein (2). Ground samples were analyzed for NO₃-N and ammonium by leaching 0.1 g of the ground sample with 2 M KCl. Nitrate-N and ammonium concentration in the leachate were determined using a Lachat autoanalyzer (Lachat Instruments, Milwaukee, WI; Method 12-107-04-1-B).Concentrations of mineral elements were determined using methods described by Gavlak et al. (8).

The experimental design was a randomized complete block with four replicates. Treatments were applied in a split-plot arrangement with fertilizer treatments as main plots and harvest dates as subplots. Statistical significance of treatment effects was assessed by analysis of variance conducted using the General Linear Models procedure of SAS (SAS Institute Inc., Cary, NC). Mean comparisons were made using an F-protected least significant difference (16). All tests of significance were made at the 0.05 probability level. Growing season rainfall was collected at a weather station about 3 km from the experimental site.

Forage Yield

Total rainfall in September and October of 2004 was lower than in 2003 (Fig. 1). Yield of stockpiled tall fescue responded to N fertilization regardless of the source (Fig. 2). Ammonium nitrate provided a greater yield response at all rates in 2003 than HLF, but responses to these N sources were similar at all rates in 2004. Fertilizer treatments affected forage yields similarly at each autumn harvest date so treatment responses were averaged over harvest date. Dry matter yield of the second harvest was 8% greater than that for the first harvest in 2003 (1342 vs. 1458 lb DM/acre), averaged over fertilizer treatments. No difference in harvest date was detected in 2004 for forage yield (P = 0.222), probably because of the below-normal rainfall in September and October.

Fig. 1. Monthly rainfall during the 2003 and 2004 growing seasons and the long-term average near Ames, IA.

Fig. 2. Forage dry matter (DM) yield of stockpiled tall fescue in the autumn of 2003 and 2004 near Ames, IA in response to three rates of high lysine fertilizer (HLF), ammonium nitrate, and calcium sulfate, averaged over harvest dates. Nitrogen application rates for HLF and ammonium nitrate were 23, 46, and 91 lb/acre. Sulfur application rates for HLF and calcium sulfate were 20, 40, and 80 lb/acre. Vertical error bars represent the LSD (0.05).

The HLF and NH₄NO₃ had similar yields in the harvest made the following spring (Fig. 3), except at the 46-lb/acre N rate in 2004. In 2005, NH₄NO₃ yielded higher than HLF when at least 46 lb of N per acre was applied the previous summer. At the 91-lb/acre N rate, NH₄NO₃ yielded 13% greater than the HLF. The potentially greater carry-over N mineralized from the organic N component of HLF was not apparent during the study period. Cogger et al. (5) reported that the apparent N recovery for tall fescue from biosolid application increased dramatically after a second application. The lack of a residual response to one HLF application demonstrates that the organic component of this by-product does not contain recalcitrant organic material that would be released over a longer time period. Although forage yield did not differ by harvest date in autumn of 2004, the spring harvest was greater when tall fescue was harvested early compared to late (1849 vs. 1622 lb DM per acre), when yields were averaged across fertilizer treatment.

Fig. 3. Residual forage dry matter (DM) yield of tall fescue in the spring of 2004 and 2005 near Ames, IA in response to three rates of high lysine fertilizer (HLF), ammonium nitrate, and calcium sulfate harvested the spring following fertilizer application. Nitrogen application rates for HLF and ammonium nitrate were 23, 46, and 91 lb/acre. Sulfur application rates for HLF and calcium sulfate were 20, 40, and 80 lb/acre. Vertical error bars represent the LSD (0.05).

There was no difference between HLF and NH₄NO₃ for total DM yield combined over autumn and spring harvests (Fig. 4) of 2003-2004 and 2004-2005. Each pound of fertilizer N applied, regardless of source, resulted in a total yield increase of 27.5 and 24.8 lb DM per acre. Singer et al. (14) reported a per-acre response of 15 to 19 lb DM per lb N for stockpiled tall fescue in the Upper Midwest for autumn harvests. The greater response reported in this study is due to inclusion of residual forage yields in spring harvests, which displayed a carry-over effect in response to summer N applications. The spring fraction of the combined autumn and spring DM yield ranged from 49 to 41% in 2003-2004 and 50 to 47% in 2004-2005 from the low to high N rate.

Fig. 4. Forage dry matter (DM) yield response of tall fescue summed over autumn and spring harvests in 2003-2004 and 2004-2005 in response to three rates of fertilizer nitrogen applied as high lysine fertilizer or ammonium nitrate near Ames, IA.

Nitrogen and Sulfur Constituents

There was a significant year by treatment by date interaction for ammonium and nitrate-N, but not for total N (Table 1). Averaged across harvest date, total N concentration increased with N fertilization rate and did not differ between N sources in 2003 (1.77, 2.01, and 2.41% for the 23-, 46-, and 91-lb/acre N rates, respectively). In 2004, HLF and NH₄NO₃ had similar total N at the 23- and 46-lb/acre N rates (1.66 and 1.86%, respectively), but NH₄NO₃ had greater total N than HLF at the 91-lb/acre N rate (2.36 vs. 1.98%). There was also a tendency for total N to decrease at the late compared to early harvest date (P = 0.052).

Ammonium concentration increased as N rate increased for the early harvest date in 2003. In 2004, tall fescue DM in the HLF and NH₄NO₃ treatments had similar ammonium concentrations at all N rates except at 91 lb/acre in the early harvest, and N rate had a less consistent effect on ammonium concentrations except for NH₄NO₃ at the 91-lb/acre N rate for both harvests. Nitrate-N concentration was higher when N at 91 lb/acre was applied as either HLF or NH₄NO₃ in 2003 for the first harvest, indicating that more N was available than could be metabolized. In both years at the early harvest, forage receiving NH₄NO₃ had higher nitrate-N concentrations than HLF at the 91-lb/acre N rate. The concentration of nitrate-N in the forage did not pose a threat for acute nitrate toxicity for grazing livestock for any treatment (3).

Sulfur concentrations exhibited year by treatment and treatment by date interactions. At the early harvest date in 2003 and 2004, adding S at 80 lb/acre in HLF increased sulfur concentration compared to the 20-lb/acre S rate, but no differences were detected between the lower two rates or the upper two rates of HLF. The 20-lb/acre S rate of HLF increased forage sulfur concentration above the control in both harvests in 2004, but only the early harvest in 2003. Sulfur concentration of forage receiving HLF was greater than that in forages receiving NH₄NO₃ at all fertilizer rates in the early harvest of both years. Calcium sulfate application increased the S concentration in the early harvest compared to the control when at least 40 lb of S per acre was applied, but had no effect in the late harvest of 2003 compared to the control. In 2004, CaSO₄ increased S concentration up to the 40-lb/acre S rate in the early harvest but S rate had no effect on S concentration in the late harvest. Only the 80-lb/acre S rate of HLF increased S concentration in the late harvest of 2003. No differences in S concentration were detected for NH₄NO₃ at the late harvest in either year or HLF in 2004.

Forage Quality

Fertilization with HLF and NH₄NO₃ increased forage quality compared to the control (Table 2). Forage fertilized with HLF and NH₄NO₃ had similar IVDMD at each fertilizer rate, averaged across year (Table 2). Digestibility only increased after applying HLF at the highest rate, whereas higher digestibility was detected by applying N at 46 lb/acre as NH₄NO₃. Averaged across N source and rate, IVDMD increased 8% compared to the control treatment. Crude protein concentration was increased by N fertilization. Increases were similar for both N sources, except for the 46-lb/acre N rate in HLF in 2004 and the 91-lb/acre N rate in HLF both years, which was lower than the same rate using NH₄NO₃ (Table 2). Application of HLF and NH₄NO₃ lowered NDF concentration compared to the control (Table 2), but generally no additional benefit for reducing NDF was derived above an N rate of 46 lb/acre. Dry matter intake of forage by grazing livestock is inversely related to NDF concentration. Animals grazing tall fescue fertilized with HLF or NH₄NO₃ would be expected to consume greater amounts of forage and perform better than those grazing unfertilized pasture. Crude protein and IVDMD were lower in forage harvested at the later date.

Sulfur fertilization with CaSO₄ had no effect on forage quality, averaged across year. Improvements in digestibility related to S fertilization of other forage species have sometimes been attributed to increasing S concentrations above levels required for microbial growth in the rumen (10). The dietary requirement for S is 0.15% for beef cattle (13). Although concentrations of S in the forage were affected by fertilization with HLF, S concentrations for all treatments were above 0.15% (Table 1).

Mineral Composition

Nitrogen fertilization had no effect on P concentration of the forage, but CaSO₄ fertilization increased it by as much as 376 ppm in 2003 (Table 3). Potassium concentration increased with N fertilization and there was no difference due to N source. Sulfur fertilization had no effect on K concentration. Averaged across year and harvest date, calcium concentration decreased with 91 lb of N per acre, regardless of the N source, compared to N application at 23 and 46 lb/acre. Calcium concentration was unaffected by S fertilization. Magnesium concentration was not affected by fertilizer treatment. Forage sodium concentration was only increased with the highest HLF application in 2003 compared to the control. Averaged across year and harvest date, applying N at 46 or 91 lb/acre as HLF increased the Cl concentration of the forage compared to the same N rates applied as NH₄NO₃. Mineral concentrations were typical of those found in cool-season grasses (15) and, with the exception of Na, were adequate to meet the dietary requirements of grazing livestock (18). The main effect of harvest date was significant for P concentration, which declined at the late harvest date. All other mineral concentrations exhibited year by date interactions that also declined at the late harvest date, except for Ca, which increased.

Summary

High lysine fertilizer provided similar total forage DM yield and forage quality as the equivalent N rate using NH₄NO₃. Using NH₄NO₃ may provide greater autumn yield, but both sources had similar yield when combining the autumn stockpiled and a spring forage harvest. Each pound of fertilizer N resulted in a yield increase of between 24.8 and 27.5 lb DM during the 2-year study period. The addition of S had no benefit on forage quality or DM yield in this study. Growers deciding between N sources should base their decisions on forage supply and cost because cumulative performance of tall fescue using both N sources was similar.

Disclaimer

Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the United States Department of Agriculture.

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