Zachary N. Senwo

Amino acid composition of soil organic matter

Abstract This study investigated the amino acid composition of soil organic matter extracted from ten surface soils in addition to surface soils from two long-term cropping systems [continuous corn (CCCC), corn-soybean-corn-soybean (CSCS), and corn-oats-meadow-meadow (COMM)] at two sites in Iowa: the Clarion-Webster Research Center (CWRC) and the Galva-Primghar Research Center (GPRC). Results showed that, with the exception of asparagine pluse aspartic acid and glutamine plus glutamic acid, the other 13 amino acids studied, expressed as perecentages of total amino acids extracted, were generally very uniform among the soils. The total amino acids extracted from the ten soils were significantly correlated with organic carbon (C) ( and clay content (, but not with total nitrogen (N), pH, or sand content. Expressed as percentages or organic C and N in soils, the amounts extracted ranged from 10.9% to 32.4% and from 12.0% to 27.4%, respectively. The amino acid N identified, expressed as percentages of organic N extracted, ranged from 32% to 50% and the C/N ratios of the extracted organic matter ranged from 10.1 to 14.9. The type of rotation did not significantly affect the total amino acid content of the soils from the same N treatment, but it did affect the total amino acid content of soils from the control plots. The total amino acids measured under the different crop rotations at the CWRC site were in the order: COMM>CCCC>CSCS. The order for the GPRC site was: CSCS>COMM>CCCC. The amino acid N identified, expressed as percentages of organic N extracted from soils at the CWRC site, ranged from 33.1% to 50% and for the GPRC site ranged from 26.5% to 51.4%. The C/N ratios of the organic matter extracted ranged from 10.4 to 14.1 and from 6.5 to 14.3 for the soils from CWRC and GPRC sites, respectively.

Proteomic Analysis of Soybean Roots under Aluminum Stress

Toxic levels of aluminum (Al) in acid soils inhibit root growth and cause substantial reduction in yields of Al-sensitive crops. Aluminum-tolerant cultivars detoxify Al through multiple mechanisms that are currently not well understood at genetic and molecular levels. To enhance our understanding of the molecular mechanisms involved in soybean Al tolerance and toxicity, we conducted proteomic analysis of soybean roots under Al stress using a tandem combination of 2-D-DIGE, mass spectrometry, and bioinformatics tools and Al-tolerant (PI 416937) and Al-sensitive (Young) soybean genotypes at 6, 51 or 72 h of Al treatment. Comparison of the protein profile changes revealed that aluminum induced Al tolerance related proteins and enzymes in Al-tolerant PI 416937 but evoked proteins related to general stress response in Al-sensitive Young. Specifically, Al upregulated: malate dehydrogenase, enolase, malate oxidoreductase, and pyruvate dehydrogenase, in PI 416937 but not in Young. These enzymes contribute to increased synthesis of citrate, a key organic acid involved in Al detoxification. We postulate that simultaneous transgenic overexpression of several of these enzymes would be a robust genetic engineering strategy for developing Al-tolerant crops.

Tillage, cropping systems, and nitrogen fertilizer source effects on soil carbon sequestration and fractions.

Quantification of soil carbon (C) cycling as influenced by management practices is needed for C sequestration and soil quality improvement. We evaluated the 10-yr effects of tillage, cropping system, and N source on crop residue and soil C fractions at 0- to 20-cm depth in Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama, USA. Treatments were incomplete factorial combinations of three tillage practices (no-till [NT], mulch till [MT], and conventional till [CT]), two cropping systems (cotton [Gossypium hirsutum L.]-cotton-corn [Zea mays L.] and rye [Secale cereale L.]/cotton-rye/cotton-corn), and two N fertilization sources and rates (0 and 100 kg N ha(-1) from NH(4)NO(3) and 100 and 200 kg N ha(-1) from poultry litter). Carbon fractions were soil organic C (SOC), particulate organic C (POC), microbial biomass C (MBC), and potential C mineralization (PCM). Crop residue varied among treatments and years and total residue from 1997 to 2005 was greater in rye/cotton-rye/cotton-corn than in cotton-cotton-corn and greater with NH(4)NO(3) than with poultry litter at 100 kg N ha(-1). The SOC content at 0 to 20 cm after 10 yr was greater with poultry litter than with NH(4)NO(3) in NT and CT, resulting in a C sequestration rate of 510 kg C ha(-1) yr(-1) with poultry litter compared with -120 to 147 kg C ha(-1) yr(-1) with NH(4)NO(3). Poultry litter also increased PCM and MBC compared with NH(4)NO(3). Cropping increased SOC, POC, and PCM compared with fallow in NT. Long-term poultry litter application or continuous cropping increased soil C storage and microbial biomass and activity compared with inorganic N fertilization or fallow, indicating that these management practices can sequester C, offset atmospheric CO(2) levels, and improve soil and environmental quality.

Influence of Tillage, Cropping, and Nitrogen Source on the Chemical Characteristics of Humic Acid, Fulvic Acid, and Water-Soluble Soil Organic Matter Fractions of a Long-Term Cropping System Study

The characterization of organic matter in agroecosystems is important because of its involvement in many important soil ecosystem processes. Humic acid, fulvic acid, and water-extractable organic matter from a 9-year agroecosystem study investigating the effects of tillage, cropping system, and N source was characterized using multidimensional fluorescence spectroscopy with parallel factor analysis (PARAFAC). The fluorescence spectra suite containing all three types of organic matter fractions was modeled by five PARAFAC components. The distribution of component concentrations was unique to each type of organic matter fraction, indicating that these operational extracted fractions reflect differing chemical pools of soil organic matter. The three treatment factors (tillage, cropping, and N source) investigated in this study did not affect the component distribution of the humic and fulvic acid fractions that are regarded as the refractory pools of soil organic matter. In contrast, the component distribution of the more labile water-extractable organic matter fraction was significantly affected by the N source treatment. The results of this study support the use of multidimensional fluorescence spectroscopy with PARAFAC as a method to investigate how management practices of agroecosystems affect the dynamics and chemical nature of soil organic matter pools.

Nitrogen and Phosphorus Accumulation in Pasture Soil from Repeated Poultry Litter Application

Poultry litter (PL) is a traditionally inexpensive and effective fertilizer to improve soil quality and agricultural productivity. However, over application to soil has raised concern because excess nutrients in runoff could accelerate the eutrophication of fresh water. In this work, we determined the contents of total phosphorus (P), Mehlich 3 extracted P, total nitrogen (N), ammonium (NH4)‐N, and nitrate (NO3)‐N, in pasture soils receiving annual poultry litter applications of 0, 2.27, 2.27, 3.63, and 1.36 Mg/ha/ yr, respectively, for 0, 5, 10, 15, and 20 years. Samples were collected from three soil depths (0–20, 20–40, and 40–60 cm) of the Hartsells series (fine‐loamy, siliceous, subactive, thermic, Typic Hapludults) on a 3–8% slope in the Sand Mountain region of north Alabama. PL application increased levels of total P, Mehlich‐3 extractable P, and total N significantly. However, the change in NH4‐N and NO3‐N contents by the PL application was not statistically significant. Correlation analysis indicated that the contents of total P, Mehlich 3 extracted P, and total N were more related to cumulative amounts of poultry litter applied than the years of application or annual application rates alone. This observation suggested that N and P from poultry litter accumulated in soil. Predicting the build‐up based on the cumulative amounts of PL application, rather than isolated factors (i.e., application year or rate), would improve the accuracy of evaluating long‐term impacts of poultry litter application on soil nutrient levels.

Enzymatic Quantification of Phytate in Animal Manure

Phytate (inositol hexaphosphate) has been identified as a major organic phosphorus (P) form in soil, animal manure, and other environmental samples. Although a number of methods are available for quantitative isolation and determination of phytate, they are time‐consuming and not amenable to routine analysis. We developed a simple, rapid method for enzymatic determination of phytate in animal manure. Animal manure was extracted by H2O, 1 M hydrochloric acid (HCl), 0.1 M sodium acetate (NaOAc, pH 5.0) with or without 0.05 M ethylenediaminetetraacetate (EDTA), and 0.25 M or 0.5 M sodium hydroxide (NaOH)–0.05 M EDTA. Extracts were diluted (1/10–1/150) and adjusted to pH 5.0 in sodium acetate buffer. The diluted extracts were then incubated at 37 °C for 1 h in the absence and presence of fungal 3‐phytase (PHY) and potato acid phosphatase (PAP). Enzymatic hydrolyzable organic P was calculated as the difference in inorganic P (Pi) between the mixtures with and without enzymes. Our data indicated that enzymatic incubation of properly diluted and pH‐adjusted HCl or NaOH/EDTA extracts released phytate P. The complementary substrate specificity of the two enzymes is considered to enhance the effectiveness of enzymatic hydrolysis. Consequently, we recommend this method of combining PAP and PHY for quantifying phytate P. Additional research is being conducted to verify the effectiveness of this method for general use across a wider range of soils and manures.

Pyrosequencing Reveals Bacteria Carried in Different Wind-Eroded Sediments

Little is known about the microbial communities carried in wind-eroded sediments from various soil types and land management systems. The novel technique of pyrosequencing promises to expand our understanding of the microbial diversity of soils and eroded sediments because it can sequence 10 to 100 times more DNA fragments than previous techniques, providing enhanced exploration into what microbes are being lost from soil due to wind erosion. Our study evaluated the bacterial diversity of two types of wind-eroded sediments collected from three different organic-rich soils in Michigan using a portable field wind tunnel. The wind-eroded sediments evaluated were a coarse sized fraction with 66% of particles >106 μm (coarse eroded sediment) and a finer eroded sediment with 72% of particles <106 μm. Our findings suggested that (i) bacteria carried in the coarser sediment and fine dust were effective fingerprints of the source soil, although their distribution may vary depending on the soil characteristics because certain bacteria may be more protected in soil surfaces than others; (ii) coarser wind-eroded sediment showed higher bacterial diversity than fine dust in two of the three soils evaluated; and (iii) certain bacteria were more predominant in fine dust (, , and ) than coarse sediment ( and ), revealing different locations and niches of bacteria in soil, which, depending on wind erosion processes, can have important implications on the soil sustainability and functioning. Infrared spectroscopy showed that wind erosion preferentially removes particular kinds of C from the soil that are lost via fine dust. Our study shows that eroded sediments remove the active labile organic soil particulates containing key microorganisms involved in soil biogeochemical processes, which can have a negative impact on the quality and functioning of the source soil.

Significance of Enzyme Activities in Soil Nitrogen Mineralization

This study was undertaken to assess the relationship between nitrogen (N) mineralization in soils treated with eight lime application rates, with four field replications, and the activities of six amidohydrolases involved in N cycling and four glycosidases involved in carbon (C) cycling in soils. Nitrogen mineralization was studied at 20 or 30 °C for 20 weeks, and with the exception of N‐aceyl‐β‐D‐glucosaminidase (NAGase; EC 3.2.1.30) activity, which was assayed at both temperatures, the enzyme activities were assayed at 30 °C at their optimal pH values. Results showed that among the eight enzyme activities studied, NAGase activity was the most significantly correlated with the cumulative amounts of N mineralized in 32 soil samples at 20 °C (r = 0.87***) and at 30 °C (r = 0.95***). The cumulative amounts of N mineralized at 30 °C were also significantly correlated with arylamidase and L‐aspartase activities, with r values of 0.61*** and 0.52**, respectively. Because NAGase activity is involved in both N and C cycling, the cumulative amounts of N mineralized at 30 °C were also significantly correlated with the activities of β‐glucosidase (r = 0.80***) and β‐galactosidase (r = 0.58***). Activities of other N enzymes that were significantly correlated with the cumulative amounts of N mineralized at 30 °C in 20 weeks were those of L‐asparaginase (r = 0.61***), urease (r = 0.57***), amidase (r = 0.54**), and L‐glutaminase (r = 0.41*). It seems that the activity of NAGase can be used as an index of N mineralization in soils.

Concentration and distribution of iron and manganese fractions in Alabama Ultisols

Information on metal forms and contributions of soil properties on metal distribution in Alabama soils is either limited or meager. This study chemically partitioned and evaluated soil Fe and Mn distributions and applied stepwise multiple regressions to identify the soil properties influencing their distributions in some Alabama Ultisols. Iron and Mn distributions among metal fractions were generally dependent on total metal content, soil properties, and degree of chemical weathering. Distributions among metal fractions showed that Fe was mainly in the residual fraction (> 85%), whereas Mn was predominantly oxide-bound and in the residual fraction (> 90%). The proportion of Fe fractions in the soils was in the order: residual > oxides (crystalline FeO, amorphous FeO, MnO) > organic > exchangeable, whereas Mn was in the order: oxide-bound (MnO, amorphous FeO, crystalline FeO,) > residual > exchangeable > organic fraction. Stepwise multiple regression analysis showed that pH accounted for 33% of the total variability in exchangeable Fe, whereas SOM accounted for 47.1% of the total variability in exchangeable Mn. Clay and sand contents accounted for 42.2 and 52.3%, respectively, of the total variability in the residual Fe fraction, whereas silt accounted for 19.7% of the total variability in residual Mn distribution in these soils.

Amino Compounds in Poultry Litter, Litter-Amended Pasture Soils and Grass Shoots

Amino compounds (ACs), i.e., amino acids and amino sugars, are the major forms of organic nitrogen (N) in animal manure and soil. To increase our understanding on the effect of long-term poultry litter (PL) application on soil AC pools and turnover, in this study, we determined the contents of 21 ACs in 23 PL samples, 15 soil samples collected from 0–20, 20–40, and 40–60 cm layers of five pasture plots with 0, 5, 10, 15 and 20 years of PL applications, and 5 grass shoot samples grown on these pasture fields. The contents of 21 ACs were simultaneously determined by methanesulfonic acid hydrolysis/extraction and anion chromatography-pulsed amperometry. PL application increased soil total and individual AC contents with a distribution pattern similar to that of AC in PL. The highest AC-N concentrations were observed in the soils with 10- or 15-year PL applications, inconsistent with the order of annual application rates or cumulative applied PL amounts. Application of PL increased the AC contents in grass shoots whereby the highest increase of most ACs was with the shoots from the fields that received PL for 5 years. These observations suggested that both freshly applied and residual PL had contributions to the soil AC-N, and that PL application also accelerated AC-N transformation in soil.