Published online 3 January 2006
Published in Agron J 98:80-84 (2006)
DOI: 10.2134/agronj2005.0039
© 2006 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Effects of Fresh and Composted Dairy Manure Applications on Alfalfa Yield and the Environment in Arizona
E. C. Martina,*,
D. C. Slacka,
K. A. Tanksleyb and
B. Bassoc
a Dep. of Agric. and Biosyst. Eng., Univ. of Arizona, Tucson, AZ 85721
b Pima Community College, Tucson, AZ 85709; and
c Dep. of Cropping Syst., For.and Environ. Sci., Univ. of Basilicata, Potenza, Italy
* Corresponding author (edmartin{at}cals.arizona.edu)
Received for publication February 2, 2005.
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ABSTRACT
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The Unified Animal Feeding Operation Strategy requires that field application of animal waste, a common fertilization and disposal practice, may not exceed crop nutrient needs. Additional guidelines set forth by the Arizona Department of Environmental Quality state that animal waste applications on agricultural fields in designated Confined Animal Feeding Operations (CAFOs) must be made in a manner such that the total N applied to the field cannot exceed the uptake from the crop grown. Because alfalfa is grown year round and can take up large quantities of N, many operators of CAFOs apply animal waste to their production alfalfa fields as method of waste disposal. In this research, fresh and composted dairy manure was applied to plots in a production alfalfa (Medicago sativa L.) field to determine the impact on alfalfa yield, soil nitrogen (N), phosphorus (P), and electrical conductivity (EC) levels and the potential for nitrate (NO3) and phosphate (PO4) leaching. Unfertilized plots were maintained as controls. Fresh and composted manure was applied to fertilized plots after each harvest at a rate intended to replace N removed from the previous cutting. After 1.5 yr and 13 cuttings, soil analysis down to 150 cm depth showed no significant difference in soil N between treatments. At study end, NO3–N made up 1.1% of total N in the fertilized plots but only 0.6% in control plots. Changes in soil N were not significant. Soil P content increased in fertilized plots but remained stable in control plots. Final soil PO4 measurements were 16, 99, and 116 kg ha–1 in the control, manure-treated, and compost-treated plots, respectively. Leachate from three drainage lysimeters contained no detectable NO3 or PO4 from any of the treatments. LSD showed no difference in EC between the beginning and the end of study, and alfalfa yield did not vary among treatments.
Abbreviations: AZSCHED, Arizona irrigation scheduling computer program • CAFO, confined animal feeding operation • DM, dry matter • EC, electrical conductivity • LSD0.05, Fisher's least significant difference • MAC, University of Arizona's Maricopa Agricultural Center • RFA, rapid flow analyzer • TKN, total Kjeldahl nitrogen
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INTRODUCTION
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NEW RULINGS from the Arizona Department of Environmental Quality state that animal waste applications to agricultural fields in designated Confined Animal Feeding Operations (CAFOs) must be made in a manner such that the total N applied to the field does not exceed the uptake from the crop grown. One crop commonly grown on CAFOs is alfalfa (Medicago sativa L.) for animal feed. Alfalfa does not require N fertilizer because it forms a symbiotic relationship with microorganisms that convert atmospheric N into amino acids, but it uses soil N when it is available in high concentrations (Phillips and DeJong, 1984). Because of its deep rooting pattern, it is often recommended to help reduce nitrate (NO3) pollution (Peterson and Russelle, 1991). In Arizona, where alfalfa is grown year round, its potential as a manure N disposal crop is high. The practice of applying animal waste to crops as a method of disposal is common (James et al., 1996, Jokela, 1992; Miller and Donahue, 1995). However, improper applications may pose a threat to environmental quality if the soil is overloaded with nutrients (Andraski et al., 2000). Nitrogen applied in excess of crop needs may leach into groundwater (Jemison and Fox, 1994), contributing to nonpoint-source pollution (Lanyon, 1994; Daliparthy et al., 1994, Daliparthy et al., 1995; Matson et al., 1997; Basso and Ritchie, 2005).
The effects of the application of raw and composted animal manures on nitrate leaching have been evaluated by several researchers, but published results are inconsistent. Leclerc et al. (1995) found lower nitrate leaching from applications of composted manure than from inorganic fertilizer supplying the same amount of N over a 5-yr rotation. Several studies report a higher risk of nitrate leaching if manure is applied to soils high in organic matter or if applications are made in autumn-winter (Chambers et al., 2000; Chalmers, 2001; Yan-Wang et al., 2002). Daliparthy et al. (1994) found that manure had no effect on alfalfa yield when applied at 112 kg N ha–1 and had decreased yields at 336 kg N ha–1, probably due to a smothering effect. Schmitt et al. (1993, 1994) conducted a 2-yr study of manure applications (28, 56, and 112 m3 ha–1) to alfalfa in Minnesota and reported a positive or neutral effect on yield and no change in soil and plant N levels. A recent study by Lloveras et al. (2004) found that swine slurry manure applied at 187.4 and 374.8 kg N ha–1 had no effect on alfalfa yield relative to a control. The N balance (estimated amount of N fixed by the crop) differed significantly between the high N application rate and the control in one of two research sites. Basso and Ritchie (2005) found that NO3–N leached from manure-, compost-, and inorganic fertilizer-treated plots at 681, 390, and 311 kg N ha–1, respectively, over 6 yr of a maize-alfalfa rotation in Michigan. Yields did not differ among treatments or between treatments and unfertilized controls.
To qualify and quantify chemical and water movement through the soil profile in situ, many researchers have used lysimeters. During the past few decades, lysimeters have been used for a variety of purposes, including evapotranspiration measurements (Ritchie and Burnett, 1968; Ritchie, 1972), nitrate leaching quantification (Reeder, 1986; Owens, 2000; Martin et al., 1994; Basso et al., 1995), and management impacts on nitrate leaching (Rasse et al., 2000). Pakrou and Dillon (2000) showed that deep monolith lysimeters provide better results for estimating drainage and N fluxes to groundwater than the use of shallow or repacked lysimeters.
In this research, the effects of the application of fresh and composted dairy manure on a production alfalfa field were examined to determine the impact on alfalfa yield; soil N, P, and electrical conductivity (EC) levels; and the potential for NO3 leaching in the arid southwest.
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MATERIALS AND METHODS
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Site Description
Alfalfa was planted on 17 Nov. 2000 at the University of Arizona's Maricopa Agricultural Center (MAC) in Maricopa, Arizona (112°10' N, 33°05' E). The site's rainfall averages slightly more than 177 mm per year, but only 210 mm of rainfall were received during the 20-mo study period. The variety planted was Mecca II seeded at a rate of 28 kg ha–1. The soil type was a Casa Grande fine-loam (mixed, hyperthermic Typic Natrargid). The research field was split into 12 plots, each 6 m wide and 137 m long. Fresh and composted manure was applied to the surface of the treatment plots after each alfalfa cutting at a rate intended to replace the total N removed by the harvest. There were three treatments: no N added (Control), composted manure (Compost), and fresh manure (Manure). The field was divided into four replicate blocks with three plots per block in a modified, randomized, complete-block design. Three lysimeters previously existed in the field—one located in each of the first three blocks. One Control (no N), one Compost, and one Manure treatment plot was randomly assigned to each lysimeter. Other treatments were randomly assigned so that each block consisted of one replicate of each treatment.
Irrigation and Fertilizer Applications
The field had a near zero slope and was surface irrigated with siphon tubes. Irrigations were scheduled using the AriZona irrigation SCHEDuling (AZSCHED) computer program (Martin et al., 2003). AZSCHED is a computer model developed at the University of Arizona that integrates weather, soil data, and crop factors to provide irrigation recommendations. Weather data, including rainfall, were obtained from the Arizona Meteorological Network (Brown, 2004) station approximately 805 m north of the field location. AZSCHED computes crop water usage using the Modified-Penman equation to determine reference crop evapotranspiration combined with a heat unit-based crop coefficient (Martin et al., 2003). Irrigation amounts and dates were calculated by AZSCHED using a maximum allowed depletion of 50% of plant available water in the crop rootzone and an irrigation efficiency of 75% (Martin, 2000).
The fresh and composted manure were from a large (
2500 head) dairy, located about 100 km northwest of MAC. The fresh manure was scrapped from the yard within 10 d of analysis and application. The composted manure was made by frequent watering and turning of a 2:1 mixture of dry manure and landscape nursery cuttings. Its age was unknown because the dairyman was constantly adding, moving, and selling the composted manure. All fresh and composted manure samples were analyzed for N content (NO3, NH4, and total N), and five samples were analyzed for phosphate (PO4) and EC levels over the course of the study.
Total Kjeldahl nitrogen (TKN) was determined using the standard digestion of Schumann et al. (1973) in conjunction with the indophenol blue procedure and the Alpkem Rapid Flow Analyzer (RFA) II (Bremner and Mulvaney, 1982). Soil NO3 was extracted with deionized water and analyzed for NO3–N via Cd reduction by a modified Griess–Ilsovay method using the Alpkem RFA II. Analysis of NH4 was done on undigested samples using a 2 M potassium chloride (KCl) extraction (Keeney and Nelson, 1982) and the Alpkem RFA II. The TKN minus the original NH4 in the sample yielded the organic N originally present in the sample. The TKN plus the NO3 equaled the total N in the sample, which was used to calculate the amount of material needed to replace the N removed in each harvest. Soluble P (Olsen P) was determined by sodium bicarbonate (NaHCO3) extraction and subsequent colorimetric analysis (Olsen et al., 1954). Electrical conductivity levels were determined using an electrical conductivity electrode (Bremner and Mulvaney, 1982) and a 1:1 ratio of fresh/composted manure to water.
All fresh and composted manure was applied with a manure spreader (Lakeside All Purpose Spreader, V-style) in one or two applications. Weights of the spreader and tractor were taken before and after applications to determine the amount of material applied. An initial application of 43 and 35 kg N ha–1 was applied to the Compost and Manure plots, respectively (differences reflect normal spreader variation), to induce the alfalfa to use soil N instead of forming N-fixing nodules.
Plant Harvest and Analysis
The alfalfa was harvested when 10% of the field was at flowering. After mowing, the alfalfa was raked into a single windrow per plot. Forage yield was determined by collecting and weighing a random 2-m length of windrow from each plot. Subsamples were collected from the yield sample, weighed, and dried for 24 h at 65°C to determine dry matter (DM) yield. Dried samples were ground using a Wiley Mill Model 4 grinder with a 0.5-mm sieve before N content determination by the Kjeldahl digestion method previously described. We assumed that organic N removed by the Kjeldahl digestions approximated the total N content of the alfalfa because preliminary assays showed that harvested alfalfa contained <0.5 mg kg–1 of NO3 or NH4. Nitrogen concentrations were used with yield data to determine the total amount of N removed in each harvest.
Soil Analysis
Soil samples were taken from the field on three separate dates using a Giddings Probe and a 50.8-mm hollow core sampler. Samples were taken in October 2000, before treatment initiation; January 2002, when the crop was partially dormant; and August 2002, at the conclusion of the study. Each time, three soil cores were taken from each plot in 15-cm increments down to 45 cm, then 30-cm increments to a depth of 150 cm. All samples were analyzed for TKN, NH4, NO3, P, and EC in the same manner as the fresh and composted manure. A bulk density of 1.5 g cm–3 was assumed for the soil based on data from Post et al. (1988). For more details on extractions and analyses, see Tanksley (2003).
Lysimeters
Stainless steel drainage lysimeters (2.0 by 1.5 m by 1.8 m deep) were installed in 1994 and filled with soil to simulate the actual soil profile (Martin et al., 1999). The tops of the lysimeters were 0.5 m below the soil surface, allowing leachate collection from 2.3 m below the soil surface (Fig. 1
). Leachate was collected in a stainless steel container below ground and measured and sampled at the surface using a vacuum pump and a 20-L plastic carboy. Although suction was used to sample the drainage water, the lysimeters were not under any suction. The lysimeters were checked weekly for leachate that was analyzed for NO3 and PO4 content using the Alpkem RFA II.
Statistical Analysis
Statistical analysis was conducted using the general linear model of SAS (PROC GLM procedures) (SAS Institute, 1996). Field replicated measurements were analyzed using Fisher's least significant difference (LSD0.05) in the analysis of variance.
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RESULTS and DISCUSSION
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Yield and Plant Analysis
Alfalfa was cut and analyzed 13 times throughout the study, yielding approximately 40 t ha–1 DM and 1.2 t ha–1 N (Table 1). Yields did not differ among treatments, except in February 2002, when manure may have protected some plants from frost damage. Yields for that cutting were 1408, 1770, and 2550 kg ha–1 DM for the Control, Compost, and Manure plots, respectively. Nitrogen removal mirrored yields (Table 1), although the difference in N removed in February 2002 was not significant.
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Table 1. Summary data for dry matter alfalfa yield, N removed in harvest, and N added through fertilization for the 13 cuttings during the study period at Maricopa, AZ, 2001–2002.
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Irrigation and Cultural Practices
Irrigations were scheduled according to the recommendations of AZSCHED, with the condition that no irrigation could be scheduled within a week of harvest. This was done so that the harvest equipment could maneuver in the field. The total irrigation depth applied over the study period was 3943 mm. The total rainfall over the study period was 210 mm. There were no additional fertilizers or chemicals added to any of the plots throughout the study period. No herbicides or insecticides were required.
Fresh and Composted Manure Analysis
Total N applications exceeded removal by 61 and 53% in the Compost and Manure treatments, respectively (Table 1). Slightly more N was applied as composted manure than as fresh manure (Table 1) due to the difficulty in applying the correct amount of material with a manure spreader. The fresh manure had a higher NH4–N content and lower NO3–N content than the composted manure (Table 1). This was expected because the composted manure had some time to mineralize the NH4 into NO3 during the composting operation. Phosphate concentration and EC was higher for the fresh manure than for the composted manure (Table 2).
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Table 2. Phosphorus concentration and electrical conductivity values for selected samples of fresh and composted manure.
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Soil Sample Analysis
Soil analysis showed no differences between plots at the beginning of the study (Table 3). Soil NH4 levels were higher at the end of the study than at the beginning but did not differ between treatments (Table 3). Nitrate levels were higher in fertilized plots than in control plots by the end of the study (Table 3). At least 98% of soil N was in the organic form for all treatments and sampling dates. Neither total N nor organic N contents differed between treatments or sampling dates (Table 3). Electrical conductivity did not differ by treatment but fell from an average of 1.1 to 0.4 dS m–1 over the course of the study (Table 3). Soil PO4–P increased over the course of the study in fertilized plots but not in unfertilized controls (Table 3).
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Table 3. Nitrogen, phosphorus, and electrical conductivity values of the soil taken at the beginning, midpoint, and end of the study at a depth of 0–150 cm.
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Lysimeters
Lysimeters did not collect sufficient leachate to induce drainage over the course of the study, reflecting proper irrigation, efficient plant water uptake, and a lack of significant rainfall. At the end of the study, the field was heavily irrigated to induce leaching. Neither NO3–N nor soluble P were detected in leachate at the respective detection limits of 0.5 and 0.25 mg kg–1 (data not shown).
Nitrogen Mass Balance
A N mass balance calculation was performed to assess N flux between the atmosphere and field. The N remaining in the soil at the end of the study was estimated by adding the N applied as fresh and composted manure to the pre-study N and subtracting the N removed by the alfalfa cutting. Table 4 shows the mean N balance, suggesting that the addition of the N to alfalfa inhibited fixation. Alfalfa in control plots fixed approximately 1152 kg N ha–1. There was no net N fixation in Compost and Manure plots, where alfalfa consumed 383 and 354 kg N ha–1, respectively. This compares with a recent report that alfalfa fixed 1098 kg N ha–1 without added fertilizer but only 427 kg N ha–1 when fertilized with 50 m3 swine slurry ha–1 (Lloveras et al., 2004).
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CONCLUSIONS
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In this research, fresh and composted dairy manure was applied to plots in a production alfalfa field following recently released CAFO guidelines to minimize the potential for nutrient contamination of the environment. This study suggests that with proper application, fresh and composted manure can be applied to alfalfa in the arid southwest with minimal risk of nitrate leaching. However, the lack of significant rainfall during the study period may have helped to mask potential leaching risks. The N mass balance analysis showed that the Control treatment fixed more N (1152 kg N ha–1) than the Manure (–359 kg N ha–1) and Compost (–383 kg N ha–1) treatments, demonstrating inhibition of biologic N-fixation by N application through organic compounds. The accumulation of P in the soil may be of concern in areas where surface water is near. Levels of 115 kg ha–1 and 99kg ha–1 of PO4–P were found in the soil of the Compost and Manure plots, respectively, at the end of the study.
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ACKNOWLEDGMENTS
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The authors wish to acknowledge the contribution of Dr. Jay Subramani for his assistance in the statistical analysis of the data presented in this paper.
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ABSTRACT
INTRODUCTION
