Sheep Grazing in a Wheat Fallow System Affects Dryland Soil Properties and Grain Yield

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1 Iowa State University From the SelectedWorks of Andrew W. Lenssen September, 2011 Sheep Grazing in a Wheat Fallow System Affects Dryland Soil Properties and Grain Yield Upendra M. Sainju, United States Department of Agriculture Andrew W. Lenssen, United States Department of Agriculture Hayes B. Goosey Erin Snyder Patrick G. Hatfield Available at:

2 Soil Fertility & Plant Nutrition Sheep Grazing in a Wheat Fallow System Affects Dryland Soil Properties and Grain Yield Upendra M. Sainju* Andrew W. Lenssen USDA-ARS Northern Plains Agricultural Research Lab North Central Ave. Sidney, MT Hayes B. Goosey Erin Snyder Patrick G. Hatfield Dep. of Animal and Range Sciences 230 Linfield Hall Montana State Univ. Bozeman, MT Sheep (Ovis aries L.) grazing, an effective method of controlling weeds and pests in a wheat (Triticum aestivum L.) fallow system, may affect dryland soil properties and wheat yield. We evaluated the effects of fallow management for weed control and soil water conservation (sheep grazing, herbicide application [chemical], and tillage [mechanical]) and cropping sequence (continuous spring wheat [CSW], spring wheat fallow [SW-F], and winter wheat fallow [WW-F]) on soil nutrients and chemical properties in the 0- to 60-cm depth and wheat yield. The experiment was conducted in a Blackmore silt loam from 2004 to 2008 in southwestern Montana. Soil P and K concentrations at 0 to 30 cm were lower in the grazing than in the chemical or mechanical treatments. In contrast, soil Na, Ca, and Mg concentrations were greater in the grazing and mechanical than the chemical treatment. Soil Mg concentration at 30 to 60 cm was greater under CSW than WW-F. Soil SO 4 S concentration varied with fallow management and cropping sequence. Soil ph, cation exchange capacity (CEC), and electrical conductivity (EC) at 0 to 15 cm were greater in the mechanical than in the chemical or grazing treatments. Annualized wheat yield was greater under CSW than SW-F or WW-F but was not affected by fallow management. Sheep grazing affected soil nutrients probably by consuming wheat residues but returning them at various levels through feces and urine. In contrast, tillage increased ph, CEC, and EC, probably by incorporating crop residue, feces, and urine into the soil. By applying enough P and K fertilizers to wheat and using less intensive grazing, sheep grazing can be used to sustain wheat yields without seriously affecting soil nutrients and chemical properties. Abbreviations: CEC, cation exchange capacity; CSW, continuous spring wheat; EC, electrical conductivity; SW-F, spring wheat fallow; WW-F, winter wheat fallow. Integrated crop livestock systems were commonly used to sustain crop and livestock production throughout the world before synthetic fertilizers were introduced in the 20th century (Franzluebbers, 2007). The system is still used in many developing countries, especially in Africa and Southeast Asia, where fertilizers are scarce and expensive (Herrero et al., 2010). Extensive application of fertilizers in the 20th century increased crop yields but reduced environmental quality by increasing (i) N leaching from the soil profile to the groundwater, (ii) surface runoff of N and P from agricultural lands to streams and lakes, causing eutrophication, and (iii) emissions of greenhouse gases such as N 2 O, (Franzluebbers, 2007; Herrero et al., 2010). Increased soil acidity following the application of commercial fertilizers, especially N fertilizers, also led to the development of infertile soils that did not respond well to increased fertilizer application for sustaining crop yields (Herrero et al., 2010). In such cases, integrated crop livestock systems can be used as an option to improve soil quality and sustain crop yields (Franzluebbers, 2007; Maughan et al., 2009). The major benefits of these systems are: (i) the production of crops, meat, and milk, (ii) the production of crop residue for animal feed, (iii) the production of manure to apply as fertilizer, (iv) the use of animals as draft power for tillage, and (v) control of weeds and pests (Franzluebbers, 2007; Hatfield et al., 2007a,c; Herrero et al., 2010). Soil Sci. Soc. Am. J. 75: Posted online 11 Aug doi: /sssaj Received 14 May *Corresponding author (upendra.sainju@ars.usda.gov). Soil Science Society of America, 5585 Guilford Rd., Madison WI USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. SSSAJ: Volume 75: Number 5 September October

3 Table 1. Monthly total precipitation from 2004 to 2008 near the experimental site. Month yr avg. mm Jan Feb Mar Apr May June July Aug Sept Oct Nov Dec Total Table 2. Soil chemical properties at the 0- to 15 and 15- to 30-cm depths at the initiation of the experiment in April Property 0 15 cm cm Organic C, g kg P, mg kg K, mg kg Ca, mg kg Mg, mg kg Na, mg kg SO 4 S, kg ha Cation exchange capacity, cmol c kg Electrical conductivity, S m ph In the northern Great Plains, wheat fallow systems have been used as the conventional dryland farming practice since the last century (Halvorson et al., 2000, 2002). In these systems, land is typically fallowed from 14 to 20 mo. Fallowing is used to conserve soil water, release plant nutrients, control weeds, increase succeeding crop yields, and reduce the risk of crop failure (Aase and Pikul, 1995; Jones and Popham, 1997). Using tillage and herbicides to control weeds on fallowed land is effective but expensive, resulting in some of the highest variable costs for small grain production in Montana ( Johnson et al., 1997). Other disadvantages of using these practices are the exposure of soil to erosion due to tillage and an increased risk of contamination of herbicides in soil and water and risks to human and animal health (Fenster, 1997). Sheep grazing during fallow periods in wheat fallow systems can be used to effectively control weeds (Hatfield et al., 2007c) and insects, such as wheat stem sawfly (Cephus cinctus Norton [Hymenoptera: Cephidae]) (Goosey et al., 2005; Hatfield et al., 2007a). During fallow, sheep usually graze on crop residues and weeds. Although grazing can reduce the quantity of crop residue returned to the soil, the number of sheep grazed per unit area can be adjusted in such a way that crop residue cover in the grazing treatment will be similar to that in a conservation tillage system where soil erosion is minimal (Hatfield et al., 2007c). Animal feces and urine returned to the soil during grazing can enrich soil nutrients, improve soil quality, and increase crop yields (Franzluebbers and Stuedemann, 2008; Tracy and Zhang, 2008; Maughan et al., 2009). The distribution of feces and urine by animals during grazing at the soil surface can be uneven; however, distribution can be more uniform with sheep than with cattle (Bos taurus L.) grazing (Abaye et al., 1997). Hatfield et al. (2007b) reported that sheep grazing during fallow to control weeds did not influence soil organic matter and nutrient levels compared with an ungrazed treatment in north-central Montana. Abaye et al. (1997) found that sheep grazing increased the soil bulk density and extractable P and grass yields compared with cattle grazing. Levels of nutrients such as P, K, Ca, Mg, and SO 4 S in the soil can influence crop yields and quality. Similarly, soil properties such as ph, CEC, and EC can affect nutrient availability and plant growth due to chemical reactions and nutrient toxicity levels. Although sheep grazing can return part of the nutrients consumed in wheat residue through feces and urine to the soil, little is known about the effect of sheep grazing on dryland soil nutrients and chemical properties and crop yields compared with tillage or herbicide application to control weeds during fallow in wheat fallow systems. We hypothesized that sheep grazing would result in similar or increased dryland soil nutrients and chemical properties and wheat yields compared with tillage or herbicide application and that the effect would be more pronounced in CSW than in SW-F and WW-F. Our objectives were to: (i) evaluate the effects of fallow management for weed control (grazing, chemical, and mechanical) and cropping sequence (CSW, SW-F, and WW-F) on dryland soil P, K, Ca, Mg, Na, SO 4 S, CEC, EC, and ph levels at the 0- to 60-cm depth and wheat grain and biomass yields from 2004 to 2008; and (ii) relate soil nutrients and chemical properties with wheat yields in southwestern Montana. MATERIALS AND METHODS Site Description and Treatments The experiment was conducted from 2004 to 2008 at the Fort Ellis Research and Extension Center, Montana State University, Bozeman (45 40 N, W; altitude 1468 m). The site has a mean monthly air temperature ranging from 5.7 C in January to 18.9 C in July. The mean annual precipitation (113-yr average) is 465 mm, 60% of which occurs during the crop growing season (April September) (Table 1). The soil is a Blackmore silt loam (a fine-silty, mixed, superactive, frigid Typic Argiustoll) with 0 to 4% slopes and contains 250 g kg 1 sand, 500 g kg 1 silt, and 250 g kg 1 clay. Soil nutrient and chemical properties of samples from the 0- to 15- and 15- to 30-cm depths taken from two composite cores per plot in the spring of 2004 before the initiation of the experiment were not significantly different among treatments. As a result, average values across treatments are shown in Table 2. Previous cropping history for the last 10 yr was perennial grass pasture containing a mixture of smooth bromegrass (Bromus inermis Leyss.), intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth & D. R. Dewey], and Canada bluegrass (Poa compressa L.), followed by 1 yr of fallow. Treatments consisted of three fallow management practices for weed control and soil water conservation (grazing, chemical, 1790 SSSAJ: Volume 75: Number 5 September October 2011

4 and mechanical) as the main plot and three cropping sequences (CSW, SW-F, and WW-F) as the split-plot arrangement in a randomized complete block with three replications. The grazing treatment consisted of grazing with a group of western whitefaced sheep at a stocking rate of 29 to 153 sheep d ha 1 during fallow periods in fenced plots. Sheep grazed on weeds and wheat residue after grain harvest during 3 out of 8 mo of the fallow period in CSW to 10 out of 20 mo in SW-F. Grazing ended when about 47 kg ha 1 or less of wheat residue and weeds remained in the plot. The chemical treatment consisted of applying herbicides, such as a mixture of glyphosate [N-(phosphonomethyl)glycine] at 1.17 L ha 1 and the dimethylamine salt of dicamba (3,6-dichloro-2-methoxybenzoic acid) at 1.75 L ha 1, to control weeds at planting and during fallow periods. The mechanical treatment consisted of tilling the plots from two times in CSW (preplanting and post-harvest) to four times (preplanting, post-harvest, and fallow periods) in SW-F and WW-F to control weeds with a John Deere 100 Flexicoil harrow (Deere & Co., Moline, IL) to a depth of 15 cm. The split-plot size was 91.4 by 15.2 m. Crop Management The rates of N fertilizer applied to spring and winter wheat ranged from 200 kg N ha 1 in CSW and WW-F to 250 kg N ha 1 in SW-F. The rates depended on yield goals, which ranged from 3.9 Mg ha 1 in CSW to 4.8 Mg ha 1 in SW-F and WW-F. Soil NO 3 N content to a depth of 60 cm measured after grain harvest in the fall every year was used to adjust the N rate before N fertilizer was applied to spring and winter wheat. Nitrogen fertilizer as urea (45% N) was broadcast in April to May to both spring and winter wheat. For spring wheat, N fertilizer was incorporated to a depth of 15 cm using the Flexicoil harrow. For winter wheat, N fertilizer was applied at the surface. Because the soil contained higher levels of extractable P and K (Table 2) (Agvise Laboratories, 2009), no P and K fertilizers were applied. From 2004 to 2008, spring wheat (cv. McNeal, foundation seed, Montana State Univ., Bozeman) was planted at 90 kg ha 1 in late April to early May and winter wheat (cv. Promontory, foundation seed, Montana State Univ., Bozeman) was planted at 73 kg ha 1 in late September to early October using a double disk opener with a row spacing of 30 cm. Growing-season broadleaf weeds were controlled with selective post-emergence herbicides. In late August to early September, 2 d before grain harvest, total wheat yield containing stems, leaves, and grains were harvested from two 0.5-m 2 quadrats. These were oven dried at 60 C for 2 to 3 d, and the dry matter yield was determined after weighing. Grain yields for spring and winter wheat (at 12 13% moisture content) were determined from an area of 1389 m 2 using a combine harvester each year. The biomass (stems + leaves) yield was determined after deducting the grain yield from the total yield. After grain harvest, wheat residue containing stems and leaves was returned to the soil, except in 2004 when straw from ungrazed plots was removed. Because of the lack of access to a no-till drill and the presence of a large amount of crop residue, all cropped plots in the chemical and mechanical treatments were tilled with a tandem disk in the late fall following grain harvest to reduce the effect of the residues on planting with a conventional-tillage planter. In the grazing treatment, cropped plots were tilled after sheep grazing in the late fall. As a result, plots with CSW, SW-F, and WW-F treatments were tilled one time after wheat harvest in the chemical and grazing treatments and from two (in CSW) to four times (in SW-F and WW-F) during the preplanting, postharvest, and fallow periods in the mechanical treatment. Soil Sampling and Analysis In September to October, 2004 to 2007, soil samples were collected from the 0- to 60-cm depth with a hydraulic probe (5-cm i.d.) attached to a truck from five places within the plot. These were divided into 0 to 15, 15 to 30, and 30 to 60 cm and composited by depth. In 2008, samples were collected from 0 to 30 cm at five places within the plot, separated into 0 to 5, 5 to 10, and 10 to 30 cm, and composited by depth. The samples were air dried, ground, and sieved to 2 mm for determining soil nutrients and chemical properties. In 2008, an additional undisturbed soil core (5-cm i.d.) was also collected from 0 to 5, 5 to 10, and 10 to 30 cm to determine the bulk density by dividing the mass of the soil oven dried at 105 C by the volume of the core. Because of the nonsignificant effects of treatments and interactions, bulk density values of 1.20, 1.34, and 1.61 Mg m 3 at 0 to 5, 5 to 10, and 10 to 30 cm, respectively, were used to convert concentrations (g kg 1 ) of nutrients to contents (kg ha 1 ). Soil samples were analyzed for Olsen P, extractable K, Ca, Mg, Na, and SO 4 S, CEC, EC, and ph at the Montana State University soil testing laboratory, Bozeman, and Agvise Laboratories, Northwood, ND. Olsen P was determined by extracting the soil with a buffered alkaline solution (NaHCO 3 NaOH) and determining the P concentration in the solution with Mb blue color by using a colorimeter, as described in Kuo (1996). Extractable K, Ca, Mg, and Na were determined by atomic absorption and flame emission spectrometry after extracting the soil with 1 mol L 1 NH 4 OAc solution (ph 7.0) (Wright and Stuczynski, 1996). Sulfate-S was determined by the methylene blue method (Tabatabai, 1996). Soil ph was determined with a ph meter in 1:2 soil/water solution. The CEC was determined by the method described by Sumner and Miller (1996) for arid region soils. The EC was determined with a conductance meter in a 1:1 soil/water paste (Rhoades, 1996). Because of staffing and budget constraints, only soil samples to a depth of 15 cm from 2004 to 2006, to 60 cm in 2007, and to 30 cm in 2008 were analyzed for P, K, and ph. Similarly, samples to a depth of 15 cm in 2006, to 60 cm in 2007, and to 30 cm in 2008 were analyzed for Ca, Mg, Na, CEC, and EC. For SO 4 S, samples to a depth of 30 cm in 2006 and 2008 and to 60 cm in 2007 were used for analysis. Data Analysis Data on soil nutrients and chemical properties at each depth and wheat grain and biomass yields were analyzed using the MIXED procedure of SAS (Littell et al., 1996). Fallow SSSAJ: Volume 75: Number 5 September October

5 Table 3. Effects of cropping sequence and fallow management practice on annualized wheat grain and biomass (stems + leaves) yields from 2004 to Cropping sequence Fallow management Year CSW SW-F WW-F Chemical Mechanical Grazing Mean Mg ha 1 Annualized grain yield aa 2.90 ac 3.53 ab 3.92 aa 4.01 aa 4.05 aa 3.99 a ba 1.83 bb 1.15 ec 1.84 ca 1.92 ba 1.90 ba 1.89 b ba 1.45 cb 1.70 db 1.89 ca 1.90 ba 1.92 ba 1.90 b cb 1.18 cc 2.95 ba 1.89 ca 2.03 ba 2.00 ba 2.00 b ba 1.56 bcc 2.22 cb 2.09 ba 2.17 ba 2.14 ba 2.13 b Mean 3.05 A 1.78 C 2.31 B 2.32 A 2.42 A 2.40 A Annualized biomass yield aa 3.10 ac 3.57 ab 3.61 aab 3.41 ab 3.89 aa 4.42 a ba 1.65 bb 1.94 bcb 2.52 ba 2.17 bca 2.19 ba 2.29 b ca 1.57 bcb 1.64 cb 1.79 bb 2.51 ba 1.87 bcb 2.06 bc da 1.55 bcb 2.25 ba 1.78 ba 2.21 bca 2.00 ba 2.00 c da 1.17 cb 1.49 cab 1.08 cb 1.91 ca 1.58 ca 1.53 d Mean 2.58 A 1.49 C 1.83 B 1.79 B 2.20 A 1.91 B CSW, continuous spring wheat; SW-F, spring wheat fallow; and WW-F, winter wheat fallow. Fallow management practices: chemical, where weeds were controlled with herbicides; grazing, where weeds were controlled with sheep grazing; and mechanical, where weeds were controlled with tillage. Numbers followed by different lowercase letters within a column in a set are significantly different at P = 0.05 by the least square means test. Numbers followed by different uppercase letters within a row in a set are significantly different at P = 0.05 by the least square means test. management was considered as the main-plot variable and a fixed effect, cropping sequence as the split-plot variable and another fixed effect, and year as the repeated-measure variable. Random variables were replication and replication fallow management. Values were averaged across cropping sequence phases and used for a cropping sequence in the analysis. For wheat grain and biomass yields, data were annualized by dividing the values by 1 in CSW and 2 in SW-F and WW-F because wheat was absent during the fallow phase in SW-F and WW-F. Means were separated by using the least square means test when treatments and interactions were significant (Littell et al., 1996). Statistical significance was evaluated at P 0.05, unless otherwise stated. RESULTS AND DISCUSSION Annualized Wheat Grain and Biomass Yields Annualized wheat grain and biomass yields varied significantly among cropping sequences and years, and biomass yield varied among fallow management practices (data not shown). Interactions were significant for cropping sequence year for grain and biomass yields, and for fallow management year for biomass yield. Averaged across fallow management practices, both annualized grain and biomass yields were greater under CSW than SW-F and WW-F in all years except in 2007, when yields were greater under CSW and WW-F than SW-F (Table 3). Averaged across cropping sequences, grain yield did not differ among fallow management practices in all years. In contrast, biomass yield was greater in the grazing than the mechanical treatment in 2004 and greater in the grazing and mechanical than the chemical treatment in In 2006, biomass yield was greater in the mechanical than the chemical or grazing treatments. Both grain and biomass yields were greater in 2004 than in other years, regardless of cropping sequence and fallow management practice. Averaged across fallow management practices and years, grain and biomass yields were in the order: CSW > WW-F > SW-F. Averaged across cropping sequences and years, biomass yield was in the order: mechanical treatment > grazing treatment = chemical treatment. The greater annualized wheat grain and biomass yields under CSW than SW-F and WW-F in all years except in 2007 was due to continuous cropping. The absence of crops during fallow reduced the annualized yields under SW-F and WW-F. This is similar to the results of various researchers in dryland cropping systems in the northern Great Plains (Aase and Pikul, 1995; Lenssen et al., 2007; Sainju et al., 2009). In 2007, lower yields under CSW and SW-F than WW-F were probably due to the distribution of precipitation during the crop growing season. Although growing season precipitation for spring wheat (April September) under CSW and SW-F in 2007 was comparable with other years, monthly precipitation in July was 3 mm in 2007 compared with 17 to 45 mm in other years (Table 1). Lower precipitation in July, an active wheat growth period, probably reduced spring wheat yields under CSW and SW-F in Growing season precipitation for winter wheat under WW-F (October of the current year to September of the following year) was much higher than for spring wheat under CSW and WW-F because of the longer growing period. In dryland cropping systems, growing season precipitation amount and distribution can influence crop yields (Halvorson et al., 2000; Sainju et al., 2009). Greater wheat grain and biomass yields in 2004 than in other years could be a result of increased precipitation (Table 1) and higher soil P and K concentrations, as shown below. The nonsignificant effect of fallow management on wheat grain yield suggests that sheep grazing did not alter grain yields compared with tillage and herbicide application methods of weed 1792 SSSAJ: Volume 75: Number 5 September October 2011

6 Table 4. Analysis of variance for soil nutrients and chemical properties at the 0- to 60-cm depth from 2004 to Source P K Ca Mg Na SO 4 S CEC EC ph 0 15 cm Cropping sequence (CS) NS NS NS NS NS NS NS * NS Fallow management (FM) NS NS NS NS * * NS * NS CS FM ** * NS NS NS NS NS NS * Year (Y) *** *** *** *** *** ** *** *** *** CS Y NS NS NS NS NS NS NS NS NS FM Y NS NS NS NS NS NS NS NS NS CS FM Y NS NS NS NS NS NS NS NS NS cm CS NS NS NS NS NS * NS NS * FM NS NS NS NS * NS NS NS NS CS FM NS NS NS NS NS NS NS NS NS Y ND ND ND ND ND ** ND ND ND CS Y ND ND ND ND ND NS ND ND ND FM Y ND ND ND ND ND NS ND ND ND CS FM Y ND ND ND ND ND NS ND ND ND cm CS NS NS NS ** NS NS NS NS NS FM NS NS * NS * NS * * NS CS FM NS NS NS NS NS NS NS NS NS * Significant at P = 0.05; NS, not significant. ** Significant at P = *** Significant at P = Cation exchange capacity. Electrical conductivity. ND, not determined. control. Several researchers (Redmon et al., 1995; Landau et al., 2007; Snyder et al., 2007) have also reported that wheat grain yields were similar to or greater with animal grazing than without. In contrast, greater biomass yield with the mechanical than with the chemical and grazing treatments was probably a result of increased root growth or greater availability of soil P and K due to the higher frequency of tillage, as shown below. The result suggests that wheat grain and biomass may not always grow in the same proportion; rather, their growth may be altered by management practices. Variations in the amounts of wheat biomass residue returned to the soil among treatments and years and the removal of residue due to consumption by sheep during grazing were expected to influence soil nutrients and chemical properties, as discussed below. Soil Phosphorus, Potassium, and ph Soil P and K concentrations and contents varied among treatments and years, with significant cropping sequence fallow management interaction at 0 to 15 cm from 2004 to 2007 and fallow management at 0 to 30 cm in 2008 (Tables 4, 5, and 6). Both concentrations and contents of P and K were normally lower in the grazing than in the chemical and mechanical treatments for all cropping sequences and depths, with significantly lower values at 0 to 15 cm under SW-F from 2004 to 2005 and at 0 to 30 cm in 2008 (Tables 5 and 6). The cropping sequence did not alter P and K levels at any depth, although the levels declined from 2004 to The lower P and K levels in the grazing than in the chemical and mechanical treatments could be a result of wheat residue removal by sheep due to consumption during grazing. This was especially noted under SW-F compared with the other cropping sequences. Although parts of the P and K from the wheat residue were returned to the soil through sheep feces and urine in the grazing treatment (Follett and Wilkinson, 1995), the amounts were probably not enough to balance nutrient levels in the soil. Most of the P and K in the wheat residue was probably used to increase sheep live weight. Ogejo et al. (2010) reported that, in a day, an average sheep of 29 kg body weight consumed 28 g P and 160 g K through feeds and returned 0.02 g P and 9.0 g K through urine and 1.9 g P and 4.1 g K through feces to the soil. This means that only 7 to 8% of P and K consumed by the sheep were returned to the soil through feces and urine. Several researchers (Lorimor et al., 2000; Smith and Frost, 2000; Barker et al., 2001) also found that sheep weighing 27 to 65 kg returned 0.9 to 4.9 g P d 1 and 2.6 to 15.1 g K d 1 through feces due to variations in diet, age, weight, and gender. The fact that grazing especially reduced the P and K levels under SW-F compared with the other cropping sequences was probably related to the amount of wheat residue returned to the soil. The wheat biomass yield was lower under SW-F than CSW or WW-F (Table 3). It could be possible that sheep grazing further reduced the amount of residue returned to the soil, thereby reducing the P and K levels under SW-F. In the chemical and mechanicals treatments, wheat residue after grain harvest was returned to the soil, except in 2004, which could have helped to maintain P and K levels through nutrient cycling in these treatments. These findings are in contrast to those reported by Hatfield et al. (2007b), who found that soil P SSSAJ: Volume 75: Number 5 September October

7 Table 5. Effects of cropping sequence and fallow management practice on soil P and K concentrations and ph at the 0- to 15-, 15- to 30-, and 30- to 60-cm depths from 2004 to Cropping Fallow P concentration K concentration ph sequence management Year 0 15 cm cm cm 0 15 cm cm cm 0 15 cm cm cm mg kg 1 CSW chemical mechanical grazing SW-F chemical mechanical grazing WW-F chemical mechanical grazing LSD (0.05) 24.3 NS NS 160 NS NS 0.22 NS NS Means CSW 70.0 a 55.7 a 29.0 a 397 a 262 a 266 a 6.86 a 6.52 a 7.18 a SW-F 72.3 a 45.2 a 24.9 a 436 a 277 a 251 a 6.74 a 6.25 b 7.00 a WW-F 70.2 a 49.4 a 26.3 a 427 a 263 a 271 a 6.81 a 6.50 a 7.19 a a ND ND 529 a ND ND 6.80 bc ND ND b ND ND 502 a ND ND 6.96 a ND ND c ND ND 322 b ND ND 6.92 ab ND ND b b c CSW, continuous spring wheat; SW-F, spring wheat fallow; and WW-F, winter wheat fallow. Fallow management practices are chemical, where weeds were controlled with herbicides; grazing, where weeds were controlled by sheep grazing; and mechanical, where weeds were controlled with tillage. NS, not significant. Numbers followed by different letters within a column in a set are significantly different at P = 0.05 by the least square means test. ND, not determined. and K concentrations were not significantly different among sheepgrazed, ungrazed, and tilled treatments under dryland cropping systems in western Montana. Their studies, however, were limited to 2 yr in contrast to the 5 yr of study in this experiment. Similarly, Li et al. (2008) reported that soil P and K concentrations were not significantly different between sheep-grazed and ungrazed regions in the desert steppe in Inner Mongolia. Continuous removal of crop residue by sheep grazing during a longer period in this experiment probably reduced P and K levels. The differences in soil and climatic conditions among locations influencing the amount of crop residue returned to the soil and sheep grazing intensity can also affect soil P and K levels. Quiroga et al. (2009) reported that 10 yr of cattle grazing did not alter the soil P concentration in grazed and ungrazed treatments in Argentina. In contrast, Niu et al. (2009) in Australia observed that soil P and K concentrations were greater in sheep-camping than in noncamping sites due to increased animal excreta. Cattle and sheep grazing in pasture can result in similar or increased soil P and K concentrations compared with ungrazed land (Mathews et al., 1994; Abaye et al., 1997). The reductions in P and K concentrations from 2004 to 2007, regardless of treatment, (Table 5) suggest that these nutrients are being constantly removed from the soil. Grain harvest can remove substantial amounts of P and K from the soil (Schomberg et al., 2009). Because P and K fertilizers were not applied to the soil due to their high initial concentrations (Table 2), reduced P and K levels from 2004 to 2007 were probably related to increased P and K removal in grain and the lack of fertilizer application to replace these nutrients in the soil. Although wheat grain yields remained similar among years, except in 2004 (Table 3), P and K fertilizers might need to be applied to crops to sustain wheat yields if soil P concentrations fall below the threshold value of 12 mg P kg 1 and K concentrations below 120 mg K kg 1 (Agvise Laboratories, 2009). Because wheat grain yield was not affected by fallow management practices, less intensive sheep grazing that returns more crop residue to the soil may be used to maintain soil P and K levels and to reduce the rates of P and K fertilization. Soil ph also varied with treatment and year, with significant cropping sequence fallow management interaction at 0 to 15 cm and cropping sequence at 15 to 30 cm (Table 4). The soil ph at 0 to 15 cm was greater in the mechanical than in the chemical or grazing treatments under CSW and WW-F and at 15 to 30 cm was greater under CSW and WW-F than SW-F (Tables 5 and 6). Averaged across treatments, the ph at 0 to 15 cm varied among years (Table 5). The greater soil ph at 0 to 15 cm in the mechanical than in the chemical or grazing treatments could be a result of mixing of the soil and wheat residue due to tillage. This was especially true under CSW and WW-F, where wheat grain and biomass yields were greater than under SW-F (Table 3). Tillage may have brought up subsurface soils containing higher concentrations of basic cations, such as Ca, Mg, and Na (Table 2), thereby resulting in greater ph at the surface in the mechanical treatment. This is 1794 SSSAJ: Volume 75: Number 5 September October 2011

8 Table 6. Effects of cropping sequence (CS) and fallow management (FM) practice on soil P, K, Mg, Na, and SO 4 S contents, ph, and electrical conductivity (EC) at the 0- to 30-cm depth in Chemical property Soil depth cm Cropping sequence Fallow management Analysis of variance CSW SW-F WW-F Chemical Mechanical Grazing CS FM CS FM P content, a 36.2 a 32.3 a 34.5 a 35.7 a 30.8 a NS NS NS kg ha a 25.9 a 27.9 a 30.4 a 29.3 a 17.8 b NS * NS a 68.9 a 78.9 a 81.2 a 80.7 a 40.1 b NS * NS K content, a 261 a 253 a 263 a 271 a 222 b NS * NS kg ha a 164 a 184 a 176 a 191 a 139 b NS * NS a 697 a 807 a 792 a 859 a 577 b NS * NS ph a 6.65 a 6.78 a 6.45 a 6.94 a 6.72 a NS NS NS a 6.43 a 6.48 a 6.31 a 6.64 a 6.51 a NS NS NS a 7.16 a 7.27 a 7.06 a 7.34 a 7.31 a NS NS NS EC, S m a a a a a a NS NS NS b ab a a a a * NS NS a a a a a 0.27 a NS NS NS Mg content, a 294 a 285 a 278 a 288 a 304 a NS NS NS kg ha a 387 a 397 a 362 b 382 ab 417 a NS * NS a 2561 a 2651 a 2619 a 2593 a 2640 a NS NS NS Na content, a 12.2 a 11.6 a 11.7 a 12.5 a 12.8 a NS NS NS kg ha a 16.4 a 16.6 a 15.2 b 15.2 b 18.4 a NS * NS a 87.5 a 83.7 a 84.8 ab 76.6 b 95.0 a NS * NS SO 4 S content, b 9.5 a 8.9 ab 8.5 ab 10.0 a 7.4 b * * NS kg ha b 8.9 ab 10.1 a 9.0 ab 10.6 a 7.1 b * * NS ab 28.8 b 40.8 a 34.0 ab 40.8 a 28.8 b * * NS * Significant at P = 0.05; NS, not significant. CSW, continuous spring wheat; SW F, spring wheat-fallow; and WW F, winter wheat-fallow. Fallow management practices: chemical, where weeds were controlled with herbicides; grazing, where weeds were controlled with sheep grazing; and mechanical, where weeds were controlled with tillage. Numbers followed by different letters within a row in a set are significantly different at P = 0.05 by the least square means test. again in contrast to that reported by several researchers (Cayley et al., 2002; Hatfield et al., 2007b; Li et al., 2008), who found that soil ph was not different among sheep-grazed, ungrazed, and tilled treatments in Australia, Mongolia, and the United States. Sheep urine and feces have ph values ranging from 8.0 to 8.3 (Ogejo et al., 2010). Because of the small amount of urine and feces returned to the soil compared with the amount of feed consumed by the sheep (Ogejo et al., 2010), sheep grazing had little impact in raising the soil ph compared with the other fallow management practices. A greater amount of basic cations through increased residue returned to the soil may have increased the ph more under CSW and WW-F than SW-F. Soil Calcium, Magnesium, Sodium, Sulfur, Cation Exchange Capacity, and Electrical Conductivity Soil Ca, Mg, Na, SO 4 S, CEC, and EC varied significantly among treatments and years at multiple soil depths (Tables 4 and 6). Soil Ca and CEC at 30 to 60 cm were greater in the mechanical than in the chemical treatment from 2006 to 2007 and at 0 to 5 cm were greater in the mechanical than in the chemical or grazing treatments under CSW and WW-F in 2008 (Tables 7 and 8). Averaged across fallow management practices, Ca and CEC at 10 to 30 cm were greater under CSW and WW-F than SW-F, but CEC at 5 to 10 cm was greater under WW-F than CSW in 2008 (Table 8). Averaged across cropping sequences, Mg at 5 to 10 cm and Na at 15 to 60 cm were greater in the grazing than the chemical or mechanical treatments, but SO 4 S at 0 to 30 cm was greater in the mechanical than the grazing treatment in 2008 (Table 6). Magnesium at 30 to 60 cm and SO 4 S at 15 to 30 cm were greater under CSW than WW-F from 2006 to 2007 (Table 7), but SO 4 S at 0 to 30 cm was greater under SW-F or WW-F than CSW in 2008 (Table 6). The EC at 0 to 15 and 30 to 60 cm was greater under SW-F and WW-F than CSW and greater in the mechanical than the chemical or grazing treatments (Tables 6 and 7). The greater Ca and Mg levels under CSW than SW-F or WW-F was probably due to the greater amount of crop residue returned to the soil (Table 3). The return of nutrient inputs through crop residue can increase soil nutrient levels (Schomberg et al., 2009). This resulted in increased CEC but decreased EC under CSW than SW-F or WW-F because CEC measures total cations (Ca, Mg, Na, and K) in the soil (Sumner and Miller, 1996) but EC measures soluble salts containing both cations and anions (Rhoades, 1996). The SO 4 S content was variable among cropping sequences. While greater SO 4 S content under CSW than WW-F from 2006 to 2007 could be a result of increased crop residue returned to the soil, greater SO 4 S content under SW-F and WW-F than CSW in SSSAJ: Volume 75: Number 5 September October

9 Table 7. Effects of cropping sequence and fallow management practice on soil Ca, Mg, and Na concentrations, SO 4 S content, cation exchange capacity (CEC), and electrical conductivity (EC) at the 0- to 60-cm depth from 2006 to Chemical property Soil depth cm Cropping sequence Fallow management Year CSW SW-F WW-F Chemical Mechanical Grazing Ca content, mg kg a 3541 a 3531 a 3591 a 3701 a 3412 a 3353 b 3783 a a 3494 a 3763 a 3607 a 3852 a 3558 a ND a 4871 a 4972 a 4265 b 5646 a 4937 ab ND 4950 Mg content, mg kg a 535 a 525 a 519 a 538 a 531 a 491 b 567 a a 714 a 699 a 691 a 703 a 756 a ND a 888 b 949 b 951 a 1023 a 967 a ND 981 Na content, mg kg a 18.0 a 17.2 a 18.3 a 16.8 a 18.5 a 16.1 b 19.7 a a 24.1 a 22.2 a 21.3 b 21.8 b 27.1 a ND a 28.6 a 27.6 a 27.4 b 28.2 ab 32.6 a ND 29.4 SO 4 S content, kg a 20.1 a 21.4 a 23.9 a 23.4 a 18.5 b 19.3 b 24.6 a ha a 14.8 ab 14.1 b 16.2 a 16.0 a 13.6 a 12.7 b 17.8 a a 31.6 a 31.4 a 30.1 a 32.6 a 29.1 a ND 30.6 CEC, cmol c kg a 23.1 a 22.9 a 23.2 a 23.9 a 22.3 a 21.8 b 24.6 a a 24.3 a 25.4 a 24.7 a 25.9 a 24.8 a ND a 32.6 a 33.6 a 30.1 b 37.6 a 33.5 ab ND 33.7 EC, S m b a a ab a b a b a a a a a a ND a a a b a ab ND CSW, continuous spring wheat; SW-F, spring wheat fallow; and WW-F, winter wheat fallow. Fallow management practices: chemical, where weeds were controlled with herbicides; grazing, where weeds were controlled with sheep grazing; and mechanical, where weeds were controlled with tillage. Numbers followed by different letters within a row in a set are significantly different at P = 0.05 by the least square means test. ND, not determined. Table 8. Effects of cropping sequence and fallow management practice on soil Ca content and cation exchange capacity (CEC) at the 0- to 5-, 5- to 10-, and 10- to 30-cm depths in Cropping Fallow Ca content CEC sequence management 0 5 cm 5 10 cm cm 0 5 cm 5 10 cm cm Mg ha 1 cmol c kg 1 CSW chemical mechanical grazing SW-F chemical mechanical grazing WW-F chemical mechanical grazing LSD (0.05) 0.27 NS NS 2.0 NS NS Means CSW 2.18 a 2.18 a 13.0 a 23.3 a 21.7 b 27.7 a SW-F 2.08 a 2.23 a 11.8 b 22.6 a 22.2 ab 25.6 b WW-F 2.10 a 2.37 a 13.0 a 22.7 a 23.5 a 27.8 a CSW, continuous spring wheat; SW F, spring wheat-fallow; and WW F, winter wheat-fallow. Fallow management practices: chemical, where weeds were controlled with herbicides; grazing, where weeds were controlled with sheep grazing; and mechanical, where weeds were controlled with tillage. NS, not significant. Numbers followed by different letters within a column are significantly different at P = 0.05 by the least square means test SSSAJ: Volume 75: Number 5 September October 2011

10 2008 may be a result of increased mineralization of organic S during fallow in 2008 with adequate precipitation (Table 1). Sulfur can be mineralized from soil organic matter and leached into the lower profile (Williams and Haynes, 1992), especially during fallow when soil temperature and water content increase, resulting in increased microbial activity (Halvorson et al., 2002). The greater Ca, SO 4 S, CEC, and EC levels in the mechanical than the chemical or grazing treatments were probably due to greater wheat biomass residue returned to the soil, followed by its incorporation into the soil due to tillage. Biomass residue returned to the soil after grain harvest was greater in the mechanical than the chemical or grazing treatments (Table 3). It could be possible that greater amount of nutrients returned to the soil through increased residue, followed by a greater turnover rate of plant nutrients to soil nutrients through higher tillage frequency, could have increased these levels in the mechanical treatment. Greater nutrient inputs from crop residues, followed by rapid mineralization of the residue due to tillage, can increase soil nutrient levels (Schomberg et al., 2009). This, however, did not occur with Mg and Na. Higher Mg and Na levels in the grazing than in the chemical or mechanical treatments might be a result of greater inputs in sheep feces and urine. It may be possible that sheep feces and urine contained comparatively higher concentrations of Mg and Na than other nutrients. Magnesium and Na concentrations were 0.76 and 80 mg kg 1, respectively, in sheep urine and 1.08 and 345 mg kg 1, respectively, in feces compared with Ca and S concentrations of 0.09 and 1.30 g kg 1, respectively, in urine and 2.58 and 0.91 g kg 1, respectively, in feces (Ogejo et al., 2010). Variations in the amounts of nutrients returned to the soil in sheep urine and feces and crop residues with sheep grazing compared with nutrients in ungrazed residues in the other fallow management practices show that grazing redistributed nutrient levels and affected soil properties. These results were in contrast to those obtained by Li et al. (2008), who reported that sheep grazing did not alter Ca, Mg, Na, or SO 4 S concentrations or EC in a desert steppe in Inner Mongolia. The reasons for increased Ca, Mg, Na, SO 4 S, and CEC levels from 2006 to 2007 were not known because wheat grain and biomass yields and precipitation were similar in 2006 and 2007 (Tables 1 and 3). CONCLUSIONS Sheep grazing to control weeds during fallow periods in wheat fallow systems had a negative ( 209 to 4%) effect on extractable soil P, K, and SO 4 S levels, a moderate ( 27 to 15%) effect on Ca, ph, CEC, and EC, and a positive (2 21%) effect on Mg and Na compared with herbicide application and tillage treatments. Such effects were probably a result of reduced wheat residue return to the soil due to consumption by sheep during grazing (for P, K, and SO 4 S), mixing of residue due to tillage (for Ca, ph, CEC, and EC), and return of nutrients to the soil through sheep feces and urine (for Mg and Na). Reduced soil P and K levels with grazing were especially noted under the SW-F system where wheat biomass residues returned to the soil were less than under the other cropping sequences. Such changes in soil properties with grazing, however, did not affect wheat grain yield, probably because the soil contained high levels of these nutrients. Annualized grain and biomass yields were greater, however, under CSW than SW-F and WW-F due to continuous cropping. The cropping sequence had a mixed effect on soil nutrients and chemical properties. Provided that adequate amounts of P and K are applied through fertilization if their levels in the soil fall below the threshold values of 12 and 120 mg kg 1, respectively (Agvise Laboratories, 2009), sheep grazing will have a minimal effect on wheat yields. The other option for maintaining soil nutrient levels and chemical properties and sustaining wheat yields would be less intensive sheep grazing that increases the amount of wheat residue and nutrients returned to the soil, which could reduce or eliminate the need for P and K fertilization. REFERENCES Aase, J.K., and J.L. Pikul, Jr Crop and soil response to long-term tillage practices in the northern Great Plains. Agron. J. 87: doi: / agronj x Abaye, A.O., V.G. Allen, and J.P. Fontenot Grazing sheep and cattle together or separately: Effects on soils and plants. Agron. J. 89: doi: /agronj x Agvise Laboratories Interpreting a soil test report. Agvise Laboratories, Northwood, ND. Barker, J.C., J.P. Jublena, and F.R. Walls Animal and poultry manure production and characterization. North Carolina State Univ. Coop. Ext., Raleigh. Cayley, J.W.D., M.R. McCaskill, and G.A. Kearney Changes in ph and organic carbon were minimal in a long-term field study in the western district of Victoria. Aust. J. Soil Res. 53: Fenster, C.R Conservation tillage in the northern Great Plains. J. Soil Water Conserv. 32: Follett, R.F., and S.R. Wilkinson Nutrient management in forages. p In R.F Barnes et al. (ed.) Forages. Vol. 2. Iowa State Univ. Press, Ames. Franzluebbers, A.J Integrated crop livestock systems in the southeastern USA. Agron. J. 99: doi: /agronj Franzluebbers, A.J., and J.A. Stuedemann Early response of soil organic fractions to tillage and integrated crop livestock production. Soil Sci. Soc. Am. J. 72: doi: /sssaj Goosey, H.B., P.G. Hatfield, A.W. Lenssen, S.L. Blodgett, and R.W. Kott The potential role of sheep in dryland grain production systems. Agric. Ecosyst. Environ. 111: doi: /j.agee Halvorson, A.D., A.L. Black, J.M. Krupinsky, S.D. Merrill, B.J. Wienhold, and D.L. Tanaka Spring wheat response to tillage and nitrogen fertilization in rotation with sunflower and winter wheat. Agron. J. 92: Halvorson, A.D., B.J. Wienhold, and A.L. Black Tillage, nitrogen, and cropping system effects on soil carbon sequestration. Soil Sci. Soc. Am. J. 66: doi: /sssaj Hatfield, P.G., S.L. Blodgett, T.M. Spezzano, H.B. Goosey, A.W. Lenssen, R.W. Kott, and C.B. Marlow. 2007a. Incorporating sheep into dryland grain production systems: I. Impact on overwintering larval populations of wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae). Small Rumin. Res. 67: doi: /j.smallrumres Hatfield, P.G., H.B. Goosey, T.M. Spezzano, S.L. Blodgett, A.W. Lenssen, and R.W. Kott. 2007b. Incorporating sheep into dryland grain production systems: III. Impact on changes in soil bulk density and soil nutrient profiles. Small Rumin. Res. 67: doi: /j.smallrumres Hatfield, P.G., A.W. Lenssen, T.M. Spezzano, S.L. Blodgett, H.B. Goosey, R.W. Kott, and C.B. Marlow. 2007c. Incorporating sheep into dryland grain production systems: II. Impact on changes in biomass and weed density. Small Rumin. Res. 67: doi: /j.smallrumres Herrero, M., P.K. Thorton, A.M. Notenbaert, S. Wood, S. Msangi, H.A. Freeman, et al Smart investments in sustainable food productions: Revisiting mixed crop livestock systems. Science 327: doi: /science Johnson, J.B., W.E. Zidack, S.M. Capalbo, J.M. Antle, and D.F. Webb Pests, pesticide use, and pesticide costs on larger central and eastern Montana farms with annually-planted dryland crops. Spec. Rep. 23. Dep. of Agric. 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11 Jones, O.R., and T.W. Popham Cropping and tillage systems for dryland grain production in the southern High Plains. Agron. J. 89: doi: /agronj x Kuo, S Phosphorus. p In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical analysis. SSSA Book Ser. 5. SSSA, Madison, WI. Landau, S., I. Schoembaum, D. Barkar, E.D. Unger, A. Genizi, and J. Kigel Grazing, mulching, and removal of wheat straw in a no-till system in a semiarid environment. Aust. J. Agric. Res. 58: doi: /ar06422 Lenssen, A.W., G.D. Johnson, and G.R. Carlson Cropping sequence and tillage system influence annual crop production and water use in semiarid Montana. Field Crops Res. 100: doi: /j.fcr Li, C., X. Hao, M. Zhao, G. Han, and W.D. Willms Influence of historic sheep grazing on vegetation and soil properties of a desert steppe in Inner Mongolia. Agric. Ecosyst. Environ. 128: doi: /j.agee Littell, R.C., G.A. Milliken, W.W. Stroup, and R.D. Wolfinger SAS system for mixed models. SAS Inst., Cary, NC. Lorimor, J., W. Powers, and A. Sutton Manure characteristics. Manure management system series. MWPS-18, Section 1. Midwest Plant Serv., Ames, IA. Mathews, B.W., L.E. Sollenberger, V.D. Nair, and C.R. Staples Impact of grazing management on soil nitrogen, phosphorus, potassium, and sulfur distribution. J. Environ. Qual. 23: doi: / jeq x Maughan, M.W., J.P.C. Flores, I. Anghinoni, G. Bollero, F.G. Fernandez, and B.G. Tracy Soil quality and corn yield under crop livestock integration in Illinois. Agron. J. 101: doi: /agronj Niu, Y., G. Li, L. Li, K.Y. Chan, and A. Oates Sheep camping influences soil properties and pasture production in an acidic soil of New South Wales, Australia. Can. J. Soil Sci. 89: doi: /cjss08004 Ogejo, J.A., S. Wildeus, P. Knight, and R.B. Wilke Estimating goat and sheep manure production and their nutrient contribution in the Chesapeake Bay watershed. Appl. Eng. Agric. 26: Quiroga, A., R. Fernandez, and E. Noellemeyer Grazing effect on soil properties in conventional and no-till systems. Soil Tillage Res. 105: doi: /j.still Redmon, L.A., G.W. Horn, E.G. Krenzer, Jr., and D.J. Bernardo A review of livestock grazing and wheat grain yield: Boom or bust. Agron. J. 87: doi: /agronj x Rhoades, J.D Salinity: Electrical conductivity and total dissolved solids. p In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical analysis. SSSA Book Ser. 5. SSSA, Madison, WI. Sainju, U.M., A.W. Lenssen, T. Caesar-TonThat, and R.G. Evans Dryland crop yields and soil organic matter as influenced by long-term tillage and cropping sequence. Agron. J. 101: doi: /agronj x Schomberg, H.H., D.M. Endale, M.B. Jenkins, R.R. Sharpe, D.S. Fisher, M.L. Cabrera, and V. McCracken Soil test nutrient changes induced by poultry litter under conventional tillage and no-tillage. Soil Sci. Soc. Am. J. 73: doi: /sssaj Smith, K.A., and J.P. Frost Nitrogen excretion by farm livestock with respect to land spreading requirements and controlling nitrogen losses to ground and surface waters: 1. Cattle and sheep. Bioresour. Technol. 71: doi: /s (99) Snyder, E.E., H.B. Goosey, P.G. Hatfield, and A.W. Lenssen Sheep grazing on wheat summer fallow and the impact on soil nitrogen, moisture, and crop yield. Proc. Am. Soc. Anim. Sci. West. Sect. 58: Sumner, M.E., and W.P. Miller Cation exchange capacity and exchange coefficients. p In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical analysis. SSSA Book Ser. 5. SSSA, Madison, WI. Tabatabai, M.A Sulfur. p In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical analysis. SSSA Book Ser. 5. SSSA, Madison, WI. Tracy, B.J., and Y. Zhang Soil compaction, corn yield response, and soil nutrient pool dynamics within an integrated crop livestock system in Illinois. Crop Sci. 48: doi: /cropsci Williams, P.H., and R.J. Haynes Balance sheet of phosphorus, sulfur, and potassium in a long-term grazed pasture supplied with superphosphate. Fert. Res. 31: doi: /bf Wright, R.J., and T.M. Stuczynski Atomic absorption and flame emission spectrometry. p In D.L. Sparks (ed.) Methods of soil analysis. Part 3. Chemical analysis. SSSA Book Ser. 5. SSSA, Madison, WI SSSAJ: Volume 75: Number 5 September October 2011