RICE CULTURE. Soil Properties and Carbon, Nitrogen, and Phosphorus Availability in White River Region Fields

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1 RICE CULTURE Soil Properties and Carbon, Nitrogen, and Phosphorus Availability in White River Region Fields M.C. Savin, P. Tomlinson, and R.J. Norman ABSTRACT About 40% of rice grown in Arkansas is produced in the White River Region; however, soil fertility remains a serious problem. Soil properties have been measured in fields typical of the region to determine if there are soil-quality parameters that are characteristic of these fields. The goal was to be able to target properties for further assessment to determine the degree to which they limit crop productivity. Soil samples were collected in the spring (preflood) and fall (post-harvest) of Microbial biomass carbon (C), dissolved organic C, inorganic nitrogen (N), and C and N cycling enzyme activities were statistically equal to or greater than those measured in the DeWitt silt loam (soil typical of the Grand Prairie Region). Total C and N and available phosphorus (P) were more variable than measured in the DeWitt soil. Bulk density was not greater in White River than the DeWitt soil, only one soil had a higher electrical conductivity, and while ph was higher in some White River soils, values ranged from 6.1 to 7.2. In general, while a greater range of values was measured among fields in the White River Region as compared to the DeWitt soil, most C, N, and P concentrations overlapped with, and were not consistently greater or less than, what was measured in the DeWitt soil. As a result, none of the measurements suggested a characteristic difference in White River Region soils. INTRODUCTION Although approximately 40% of the total rice crop in Arkansas is produced in the White River Region, rice yields are commonly lower than average yields in other 315

2 AAES Research Series 550 systems such as the Grand Prairie. Problems common to the White River Region include low soil fertility, alkaline soils with seasonal salinity problems, weed control problems, heavy disease pressure, and variability within fields. Because of these problems soils have been managed intensively, and while there are productive counties in this region, the long history of intensive rice production has no doubt led to a reduction in soil quality. Crop yield potential is affected not only by the above-mentioned problems, but can be diminished when soil quality is reduced. Soil quality can be defined as the ability of a soil to perform essential ecosystem services (Karlin et al., 1997), in this case plant growth or specifically, rice crop production. Soil properties were measured in 2005 (see Savin et al., 2006) and 2006 to characterize biological, physical, and chemical soil properties from fields typical of the White River Region. The ultimate goal is to be able to improve the soil quality of White River Region fields to enhance the soil fertility, consistently increase crop yields, and reduce variability within fields, thus alleviating three problems common to the White River Region. In this paper, we report properties related to C, N, and P in soils specifically selected for sampling in 2006 because yields have been below expected and cannot be explained easily due to disease, weed pressure, or management practices. Values for soil properties are compared among White River Region fields and to a DeWitt silt loam soil collected in the Grand Prairie Region. The objective was to determine whether properties can be targeted for future analysis and soil quality impovement. PROCEDURES Five growers fields in the White River Region selected by Arkansas county extension agents were sampled to a depth of 10 cm in April or May of 2006 before fields were flooded. Two of those fields were sampled previously in The other three grower fields were specifically chosen because of yield problems that have not been easily explained. Four of the fields grew rice and were resampled after harvest in early October. Soils included a Foley-Calhoun (Fc) and Lafe silt loam, and Foley-Calhoun- McCrory (Fm) complex in Jackson County, and what was predominantly mapped as a Jackport silty clay loam and Henry silt loam in Poinsett County. In addition, fields (two in the spring and one in the fall) in Arkansas County at the Rice Research and Extension Center in Stuttgart (DeWitt silt loam) were sampled as soil typical of the Grand Prairie to provide a comparison to the White River Region soils. Eight soil cores were collected from across a field and composited per replication and three replications were collected per field. There was one exception to the sampling design in spring One field was subdivided into plots that were sampled separately for each replication because of an experiment in progress (Henry silt loam). Plot boundaries were no longer marked during the fall sampling, so samples were composited from across the field, similar to the sampling protocol used in all other fields. In addition to the 2006 samples, soil had been sampled in ten fields in 2005 (eight White River Region fields and two DeWitt silt loam fields in Stuttgart) in the same manner described here (see Savin et al., 2006). Ranges of values for both spring and fall across 316

3 B.R. Wells Rice Research Studies 2006 both years are reported in this paper with White River Region soils separated from the Stuttgart DeWitt silt loam soils. The following soil properties were measured. Bulk density was obtained by ovendrying a known volume of soil (5-cm dia, 10-cm length cores). Particle size distribution was measured using the hydrometer method (Arshad et al., 1996). Urease enzyme activity was measured by production of ammonium following incubation of soil with added urea (Tabatabai, 1994). The other three enzyme activities were based on the production of the colored compound p-nitrophenol after cleavage of a substrate (Parham and Deng, 2000; Tabatabai, 1994). Values for ph and EC were obtained using 1:10 (wt:vol) soil:water ratios and measured by electrode and ph meter and by conductivity meter. Microbial biomass C and N were obtained using the chloroform-fumigation-extraction method (Vance et al., 1987; Cabrera and Beare, 1993), with dissolved organic C (DOC) measured in the filtered, unfumigated soil extracts. Filtered 1:10 (wt:vol) soil:2 M KCl extracts were analyzed colorimetrically for nitrate and ammonium (Mulvaney, 1996) using a nutrient autoanalyzer (Skalar Instruments, Norcross, Ga.). Potentially mineralizable N was measured as the production of ammonium-n following a 7-day incubation at 40 C under waterlogged conditions (Bundy and Meisinger, 1994). Filtered and acidified water-soluble P (1:10 soil:di water ratio) was measured colorimetrically (Self-Davis et al., 2000) on a nutrient autoanalyzer (Skalar Instruments, Norcross, Ga.). Mehlich-III-extractable P was analyzed on filtered extracts (1:10 soil:extract (wt:vol) ratio) (Mehlich, 1984) by inductively coupled plasma-emission spectroscopy (Spectro Analytical Instruments, Fitchburg, Mass.). Each property was compared among fields in 2006 in the spring and again in the fall using PROC GLM in SAS and least significant differences to separate means (P < 0.05). RESULTS AND DISCUSSION The range of values for properties measured among all soils collected in 2005 and 2006 in the White River Region was greater than in the DeWitt soil (Table 1). In 2006, all soils except one were classified as silt-loam by particle-size analysis. The predominantly Jackport silty clay loam was classified as a clay loam. Although there were differences among fields, ph in White River was equal to or higher than DeWitt soil and all values ranged from 5.6 to 7.2 (Table 2). Electrical conductivity (EC) was under 1.4 ds/m, and bulk density was 1.2 to 1.3 g cm -3 in all fields. While there were significant differences among fields in the fall, no White River fields had a higher bulk density than the Dewitt soil. Values were 1.0 and 0.1 % or less for soil C and N, respectively, with the lowest total C and N measured in Jackport soil and the highest in the Henry and Fm complex; these three soils represented the problem fields (Tables 2 and 3). For C pools, most soils had similar-sized microbial biomass (C mic ), with one exception, the Fm complex. Biomass in that soil in the spring was more than twice the amount measured in other soils. Soils with greater microbial biomass are considered to be healthier than soils with lower biomass because microbes retain nutrients in a relatively labile form. However, in the fall C mic was lower and not different among 317

4 AAES Research Series 550 fields. Microbial biomass N (N mic ) concentrations tended to increase in White River soils from spring to fall, with N mic being as high or higher in White River soil compared to the DeWitt silt loam in the fall (Table 3). Because C mic did not increase, this suggests a shift away from fungal contributions towards more bacteria during the growing season. Because fields were flooded throughout summer, anaerobic bacteria could have been active while aerobic organisms such as fungi were inhibited. In addition to immobilizing nutrients, microorganisms are the primary agents responsible for decomposition and nutrient cycling. Dissolved organic C was measured as an amount of substrate in soil solution (thus potentially available for decompostion by microbes). While the two fields with DeWitt soil were different than each other in the spring, DOC was not significantly different between White River and DeWitt soils, and there were no differences in DOC among any fields in the fall (Table 2). Inorganic N concentrations (nitrate plus ammonium) also tended to be lower in the fall (Table 3). One field with Dewitt soil had the highest inorganic N, but the lowest potentially mineralizable N (Table 3). In contrast, the other field with DeWitt soil had relatively low inorganic N, but among the highest potentially mineralizable N. This inverse relationship between inorganic N and potentially mineralizable N was not observed in the White River soil; however, inorganic N was not significantly lower than the Dewitt silt loam in the spring or fall. Because nutrient concentrations provide a measure of the size of pools but not activity in the soil, enzymes were measured. Urease catalyzes the breakdown of urea (important following urea fertilization) and is presumed to be ubiquitous in surface soils while β-glucosaminidase (NAGase) is involved in the breakdown of chitin, an abundant polymer of amino sugars in soil. Urease activity was similar between the DeWitt and White River soils in the spring, but was markedly lower in the DeWitt soil in the fall (Table 3). Similar to available N concentrations, NAGase was significantly different among fields in the spring, but no fields had lower activity than the DeWitt soil and activity was similar across all fields in the fall. There were more significant differences in P among fields in the spring and fall than C and N, and there were White River fields with significantly higher and lower Mehlich-III-extractable P (M-3 P) and water-soluble P (WSP) than in DeWitt soil (Table 4). There was a positive linear relationship between WSP and M-3 P (data not shown), but not between P availability and enzyme activity as soils with the lowest phosphatase did not necessarily have the lowest available P (Table 4). Furthermore, the DeWitt soil was significantly lower in alkaline phosphatase (microbially associated enzyme) in both spring and fall than all White River soils. SIGNIFICANCE OF FINDINGS This study was undertaken because rice is grown on silt-loam topsoil overlying clay layers in both the Grand Prairie and White River regions, but fields in the two regions do not perform the same. Our goal was to identify soil properties that could be targeted to improve soil quality to alleviate yield limitations in White River Region 318

5 B.R. Wells Rice Research Studies 2006 soils. After the 2005 sampling, it was determined that properties were just as variable among fields, even within the same soil type, as between ecological regions (Savin et al., 2006). Fields sampled in 2006 were chosen specifically because of unexplained rice yield problems. Similar to results in 2005, properties were variable among fields in 2006, and exhibited greater variability among White River Region soils than measured in the DeWitt (Grand Prairie) soil (Table 1). This is not unexpected because a greater number of fields were sampled in the White River Region. Despite the variability, in general, a similar range in values was measured for White River and DeWitt soils. Appropriate methods to improve fertility and consistency of yields are more likely to be successful if limiting soil properties are improved. In this study, we quantified levels of several properties including some dynamic ones related to C, N, and P availability and cycling, and did not detect consistently lower (or higher) values in White River Region soils than in DeWitt soil. Futher analysis of how the interactions of several properties and processes combine to affect rice yields, and studies targeting the availability of micronutrients, may reveal limitations in regard to fertility problems. ACKNOWLEDGMENTS This project was funded by the Rice Research and Promotion Board and the University of Arkansas Division of Agriculture. The authors greatly appreciate the assistance of Arkansas county extension agents Rick Thompson, Craig Allen, and Randy Chlapecka for finding appropriate fields and assisting with sample collection, and for growers in the selected counties who allowed access to their fields. We appreciate the technical assistance of R. Maricela Blair, Aaron Daigh, Nick Pairitz, and Ashley Rashé. LITERATURE CITED Arshad, M.A., B. Lowery, and B. Grossman Physical tests for monitoring soil quality. pp In: J.W. Doran and A.J. Jones (eds.). Methods for Assessing Soil Quality. SSSA Spec. Publ. 49. SSSA, Madison, Wis. Bundy, L.G. and J.J. Meisinger Nitrogen availability indices. pp In: R.W. Weaver, S. Angle, P. Bottomley, D. Bezdicek, S. Smith, A. Tabatabai and A. Wollum (eds.). Methods of Soil Analysis, Part 2 Microbiological and Biochemical Properties. Soil Science Society of America, Madison, Wis. Cabrera, M.L. and M.H. Beare Alkaline persulfate oxidation for determining total nitrogen in microbial biomass extracts. Soil Science Society of America Journal 57: Karlen, D.L., M.J. Mausbach, J.W. Doran, R.G. Cline, R.F. Harris, and G.E. Schuman Soil quality: A concept, definition, and framework for evaluation. Soil Science Society of America Journal 61:4-10. Mehlich, A Mehlich 3 soil test extractant: A modification of Mehlich 2 extractant. Communications in Soil Science and Plant Analysis 15:

6 AAES Research Series 550 Mulvaney, R.L Nitrogen--Inorganic forms. pp In: D.L. Sparks, A.L. Page, P.A. Helmke, R.H. Loeppert, P.N. Soltanpour, M.A. Tabatabai, C.T. Johnston and M.E. Sumner (eds.). Methods of Soil Analysis, Part 3. Chemical Methods. Soil Science Society of America, Madison, Wis. Parham, J.A. and S.P. Deng Detection, quantification and characterization of β-glucosaminidase activity in soil. Soil Biology and Biochemistry 32: Savin, M.C., P.J. Tomlinson, and R.J. Norman Labile C and N pools in soil quality assessment of White River Region fields. In: R.J. Norman, J.-F. Meullenet, and K.A.K. Moldenhauer (eds.). B.R. Wells Rice Research Studies University of Arkansas Agricultural Experiment Station Research Series 540: , Fayetteville, Ark. Self-Davis, M.L., P.A. Moore, Jr., and B.C. Joern Determination of waterand/or dilute salt-extractable phosphorus. In: G.M. Pierzynski (ed.). Methods of Phosphorus Analysis for Soils, Sediments, Residuals, and Water. [Online]. Available by Southern Extension/Research Activity - Information Exchange Group (SERA-IEG) 17 Tabatabai, M.A Soil enzymes. pp In: R.W. Weaver (ed.). Methods of Soil Analysis: Microbial and Biochemical Properties. Part 2. Soil Science Society of America, Madison, Wis. Vance, E.D., P.C. Brookes, and D.S. Jenkinson An extraction method for measuring soil microbial biomass C. Soil Biology and Biochemistry 19:

7 B.R. Wells Rice Research Studies 2006 Table 1. Ranges of values measured for soil properties in spring and fall of 2005 and 2006 for White River soils compared to those in the DeWitt soil (representing the Grand Prairie region). Property z White River Grand Prairie ph EC (ds m -1 ) Bulk density (g cm -3 ) Sand (%) Silt (%) Clay (%) Total soil C (%) C mic (µg C g -1 ) DOC (µg C g -1 ) M-3 P (µg P g -1 ) WSP (µg P g -1 ) Alkaline Pase (µg nitrophenol g -1 hr -1 ) Acid Pase (µg nitrophenol g -1 hr -1 ) Total soil N (%) N mic (µg N g -1 ) NO 3 (µg N g -1 ) NH 4 (µg N g -1 ) Ni (µg N g -1 ) Potentially min. N (µg N g -1 ) Urease (µg NH 4+ -N g -1 hr -1 ) NAGase (µg nitrophenol g -1 hr -1 ) z Abbreviations for properties include: electrical conductivity (EC), microbial biomass carbon (C mic ), dissolved organic carbon (DOC), Mehlich-III-extractable phosphorus (M-3 P), water soluble phosphorus (WSP), phosphatase (Pase), microbial biomass nitrogen (N mic ), nitrate (NO 3- ), ammonium (NH 4+ ), inorganic nitrogen (Ni), mineralizable nitrogen (min. N), and β-glucosaminidase (NAGase). 321

8 AAES Research Series 550 Table 2. Total soil C, microbial biomass C (C mic ), dissolved organic C (DOC), ph, electrical conductivity (EC), and bulk density in eight fields in three Arkansas counties in the spring (preflood) and fall (post-harvest) of 2006 (n=3). Total C C mic DOC ph EC Bulk density County/Soil z Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall (%) (µg C g -1 ) (ds m -1 ) (g cm -3 )---- Arkansas 1/DeWitt 0.85bc y NA x 51.9b NA 22.52b NA 6.0d NA 0.51e NA 1.22a NA Arkansas 2/DeWitt 0.87b NA 50.6b NA 33.62a NA 5.6e NA 0.76bc NA NA NA Arkansas3/DeWitt NA 0.71b NA 42.2a NA 25.27a NA 5.9c NA 0.66b NA 1.31a Jackson 1/Fc w 0.77cd 0.72b 44.8b 60.6a 14.14b 13.28a 6.7a 7.2a 0.56de 0.68b 1.31a 1.24ab Jackson 2/Lafe 0.70d NA 46.0b NA 24.20b NA 6.2cd NA 0.74bc NA 1.27a NA Jackson 3/Fm 0.92b 0.92a 119.3a 51.8a 35.73a 24.24a 6.3bcd 6.1c 0.85b 0.71b 1.31a 1.25ab Poinsett 1/Jackport c 47.4b 50.1a 18.61b 23.63a 6.5ab 7.2a 1.20a 1.37a 1.27a 1.18b Poinsett 2/Henry 1.03a 1.00a 48.2b 64.3a 13.15b 15.19a 6.4bc 6.7b 0.65cd 0.71b 1.31a 1.28a z The last three soils listed in the column were the poor-yielding producer fields. y Different letters within a column indicate significant differences in that property among fields (P < 0.05). x NA = not applicable. w Fc soil is Foley-Calhoun and Fm soil is a Foley-Calhoun-McCrory complex. 322

9 B.R. Wells Rice Research Studies 2006 Table 3. Total soil N, microbial biomass N (N mic ), inorganic N (nitrate plus ammonium), potentially mineralizable N (Pot. N min ), and urease and β-glucosaminidase (NAGase) activities for eight fields in three Arkansas counties in the spring (preflood) and fall (post-harvest) of 2006 (n=3). Total N N mic Ni Pot. N min Urease NAGase County/Soil z Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall Spring Fall (%) (µg N g -1 + ) (µg NH 4 -N g -1 hr -1 ) --- (µg g -1 hr -1 )- Arkansas 1 /DeWitt 0.09ab y NA x 5.2c NA 28.59a NA 3.9d NA 12.53b NA 28.10c NA Arkansas 2 /DeWitt 0.09ab NA 7.6ab NA 6.69d NA 22.4a NA 14.31b NA 19.28d NA Arkansas 3 /DeWitt NA 0.08b NA 6.1c NA 3.12ab NA 9.7a NA 3.44c NA 16.75a Jackson 1 /Fc w 0.08b 0.07b 5.0c 9.2ab 4.67d 3.67a 12.4bc 8.9a 9.53b 17.28a 18.87d 14.52a Jackson 2 /Lafe 0.09a NA 6.2bc NA 13.26c NA 12.7bc NA 11.16b NA 27.75c NA Jackson 3/ Fm 0.10a 0.10a 9.2a 7.5bc 18.73b 1.50b 18.5a 16.9a 11.39b 12.39b 25.70c 21.10a Poinsett 1 /Jackport 0.06c 0.06c 2.0d 7.0c 3.00d 1.94ab 6.2cd 7.2a 9.52b 19.91a 36.80b 14.12a Poinsett 2 /Henry 0.10a 0.09a 6.6abc 10.0a 6.97d 3.19ab 16.2ab 10.1a 24.39a 17.96a 44.47a 19.07a z The last three soils listed in the column were the poor-yielding producer fields. y Different letters within a column indicate significant differences in that property among fields (P < 0.05). x NA = not applicable. 323

10 AAES Research Series 550 Table 4. Mehlich-III P (M-3 P), water soluble phosphorus (WSP), and alkaline and acid phosphatase (Pase) in eight fields in three Arkansas counties in the spring (pre-flood) and fall (post-harvest) of 2006 (n=3). M-3 P WSP Acid Pase Alkaline Pase County/soil z Spring Fall Spring Fall Spring Fall Spring Fall (µg P g -1 ) (µg nitrophenol g -1 hr -1 ) Arkansas 1/DeWitt 27.04c y NA x 1.39c NA a NA 10.32de NA Arkansas 2/DeWitt 16.48de NA 1.81bc NA ab NA 0.00e NA Arkansas 3/DeWitt NA 18.21c NA 1.62a NA c NA 19.98d Jackson 1/Fc w 37.93b 35.05a 3.22a 1.83a c b 55.54abc 79.22ab Jackson 2/Lafe 13.70e NA 0.42d NA a NA 50.37bc NA Jackson 3/Fm 10.17f 9.71d 0.18d 0.18c ab a 30.40cd 41.52c Poinsett 1/Jackport 19.05d 16.08c 1.92b 0.87b 82.50d 67.36d 58.70ab 68.28b Poinsett 2/Henry 39.32a 25.74b 1.93b 0.48c b ab 84.01a 84.77a z The last three soils listed in the column were the poor-yielding producer fields. y Different letters within a column indicate significant differences in that property among fields (P < 0.05). x NA = not applicable. w Fc is Foley-Calhoun and Fm soil is a Foley-Calhoun-McCrory complex. 324