Evaluation of the soil rhizosphere has been limited by the lack of robust assessments that can explore the vast complex structure and diversity of soil microbial communities. Our objective was to combine fatty acid methyl ester (FAME) and pyrosequencing techniques to evaluate soil microbial community structure and diversity. In addition, we evaluated biogeochemical functionality of the microbial communities via enzymatic activities of nutrient cycling. Samples were taken from a silt loam at 0–10 and 10–20 cm in an organic farm under lettuce (Lactuca sativa), potato (Solanum tuberosum), onion (Allium cepa L), broccoli (Brassica oleracea var. botrytis) and Tall fescue pasture grass (Festuca arundinacea). Several FAMEs (a15:0, i15:0, i15:1, i16:0, a17:0, i17:0, 10Me17:0, cy17:0, 16:1ω5c and 18:1ω9c) varied among the crop rhizospheres. FAME profiles of the soil microbial community under pasture showed a higher fungal:bacterial ratio compared to the soil under lettuce, potato, onion, and broccoli. Soil under potato showed higher sum of fungal FAME indicators compared to broccoli, onion and lettuce. Microbial biomass C and enzyme activities associated with pasture and potato were higher than the other rhizospheres. The lowest soil microbial biomass C and enzyme activities were found under onion. Pyrosequencing revealed significant differences regarding the maximum operational taxonomic units (OTU) at 3% dissimilarity level (roughly corresponding to the bacterial species level) at 0–10 cm (581.7–770.0) compared to 10–20 cm (563.3–727.7) soil depths. The lowest OTUs detected at 0–10 cm were under broccoli (581.7); whereas the lowest OTUs found at 10–20 cm were under potato (563.3). The predominant phyla (85%) in this soil at both depths were Bacteroidetes (i.e., Flavobacteria, Sphingobacteria), and Proteobacteria. Flavobacteriaceae and Xanthomonadaceae were predominant under broccoli. Rhizobiaceae, Hyphomicrobiaceae, and Acidobacteriaceae were more abundant under pasture compared to the cultivated soils under broccoli, potato, onion and lettuce. This study found significant differences in microbial community structure and diversity, and enzyme activities of nutrient cycling in this organic farming system under different rhizospheres, which can have implications in soil health and metabolic functioning, and the yield and nutritional value of each crop.

Nitrogen (N) management and spatial variability of soils have received considerable attention in recent years. The effect of long‐term cropping systems on net N mineralization was studied in soils obtained from replicated plots from two sites: Galva‐Webster Research Center (CWRC site) at Kanawha and Galva‐Primghar Research Center (GPRC site) at Sutherland in Iowa, USA. Each experiment consisted of three cropping systems: continuous corn (CCCC), corn‐soybean‐corn‐soybean (CSCS), and corn‐oats‐meadow‐meadow (COMM), and treated before corn with (+N) and without (0N) ammoniacal fertilizer. Other studies involved assessing the effect of eight lime application rates (0–17,920 kg ha⁻¹ effective calcium carbonate equivalent, ECCE) on net N mineralization and nitrification in soils at the Northeast Research Center (NERC site) at Nashua, Iowa. The means of cumulative N mineralized at 30°C for 24 weeks in soils from the CWRC and GPRC sites, expressed as percentage of organic N, were generally greater in N‐treated plots than in control plots. The greatest amounts of N mineralized were in soils from the COMM rotation plots. Application of the log transformation of the data to calculate the potential mineralizable N (N _o) and the first‐order constants (k) showed that the data obeyed the exponential equation model. Expressed as percentages of total organic N in soils, the cumulative amounts of N mineralized ranged from 2.7 to 3.4% at 20°C and from 5.8 to 7.5% at 30°C. The cumulative amounts of N mineralized at 20°C and 30°C in soils from the plots under CSCS rotation were not affected by lime application. The Q₁₀ values of N mineralization ranged from 1.9 to 2.2. Increasing the rate of lime application decreased the N _o values at 20°C, but not at 30°C. Liming soils markedly increased the nitrification rate, from 27% of the NH₄ ⁺‐N added for untreated soils (0 kg ECCE ha⁻¹) to 76% for the soil treated with 17920 kg ECCE ha⁻¹. N mineralization and nitrification rates varied among the replicated plots.

Problems arising from conventional tillage (CT) systems (such as soil erosion, decrease of organic matter, environmental damage etc.) have led many farmers to the adoption of no-till (NT) systems that are more effective in improving soil physical, chemical and microbial properties. Results from this study clearly indicated that NT, mulch tillage (MT), and winter rye cover cropping systems increased the activity of phosphatase, β-glucosidase and arylsulfatase at a 0–10 cm soil depth but decreased the activity of these enzymes at 10–20 cm. The increase in enzyme activity was a good indicator of intensive soil microbial activity in different soil management practices. Poultry litter (PL) application under NT, MT, and rye cropping system could be considered as effective management practices due to the improvement in carbon (C) content and the biochemical quality at the soil surface. The activities of the studied enzymes were highly correlated with soil total nitrogen (STN) soil organic carbon (SOC) at the 0–10 cm soil depth, except for acid phosphatase where no correlation was observed. This study revealed that agricultural practices such as tillage, PL, and cover crop cropping system have a noticeable positive effect on soil biochemical activities under cotton production.

Poultry litter, an inexpensive source of nutrients and available in abundant amounts in the southeastern USA, may increase N cycling and reduce N losses compared with inorganic N fertilization if applied for crop production. We evaluated the effect of long‐term application of poultry litter and inorganic N fertilizer on crop N uptake, soil N fractions, and N losses in conservation and conventional tillage with or without cover crop at the 0‐ to 20‐cm depth in a Decatur silt loam (clayey, kaolinitic, thermic, Typic Paleudults) in northern Alabama. 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 NH₄NO₃ and 100 and 200 kg N ha⁻¹ from poultry litter). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH₄–N, and NO₃–N. Crop N uptake varied among treatments and years and total uptake from 1997 to 2005 was greater in rye/cotton–rye/cotton–corn than in cotton–cotton–corn and greater with NH₄NO₃ than with poultry litter at 100 kg N ha⁻¹ After 10 yr, STN and PON contents at 0 to 20 cm were greater in NT with poultry litter than in other treatments, except in CT with poultry litter, resulting in N storage at 38 kg N ha⁻¹ yr⁻¹ with poultry litter compared with loss at 4 kg N ha⁻¹ yr⁻¹ with NH₄NO₃. The MBN, PNM, and NO₃–N contents were greater with poultry litter than with NH₄NO₃, regardless of tillage. Calculation of estimated N balance showed that poultry litter conserved N at 191 to 556 kg N ha⁻¹ compared with –75 to 201 kg N ha⁻¹ with NH₄NO₃. Poultry litter application can increase soil N storage and mineralization and reduce the potential for N loss compared with inorganic N fertilization, thereby reducing the need for N fertilization and environmental N contamination.

The enzyme maltase (glucoinvertase; glucosidosucrase; maltase-glucoamylase; α-glucopyranosidase; glucosidoinvertase; α-d-glucosidase; α-glucoside hydrolase; α-1,4-glucosidase EC 3.2.1.20), is involved in the exo-hydrolysis of 1,4-α-glucosidic linkages and certain oligosaccharides into glucose which is an important energy source for soil microbes. This enzyme originates from different sources, which include plants, seaweeds, protozoa, fungi, bacteria, vertebrates, and invertebrates. The assay of soil maltase using maltose as substrate and the released glucose determined using a glucose oxidase–peroxidase system has not been explored or investigated to the best of our knowledge. A simple assay protocol using this system is proposed to evaluate and characterize maltase activity in soils. The protocol involves the release of glucose (determined using a glucose oxidase–peroxidase colorimetric approach) when 1 g soil is treated with toluene and incubated with 5 mM maltose in 67 mM sodium acetate buffer (pH 5.0) at 37 °C for 1 h. The optimal activity using this procedure was at pH 5.0 and decreased at temperatures above 70 °C. The calculated K_m values ranged from 0.8 to 6.5 mM, and are comparable to those of enzymes purified from microorganisms. The Arrhenius equation plots for the activity in the four soils were linear between 20 and 70 °C. The activation energy values ranged from 34.1 to 57.2 kJ mol⁻¹, the temperature coefficients (Q₁₀) ranged from 1.5 to 1.9 (avg. = 1.7), and the coefficients of variation (CV) of the proposed assay protocol for the soils used was <6%. While we recognize the availability of established assay protocols to determine soil α-glucosidase (referred in other literature as maltase) activity based on the p-nitrophenol (artificial product) released from p-nitrophenyl-α-d-glucopyranoside (artificial substrate), our interest was to assay its activity by determining the glucose (natural product) released from maltose (natural substrate).