Soil Freeze-Thaw Processes: Implications for Nutrient Cycling

Soil freeze-thaw processes can regulate nutrient availability to plants by influencing nutrient leakage from plant tissues, nutrient release from soil organisms, mineral weathering, various inorganic nutrient transformations, and nutrient transport in both soil solution and sediment. These aspects of freeze-thaw processes are given in this review. A frequently reported observation is that soil water content controls the extent of freeze-thaw impacts on several chemical, physical, and biological processes and components important for nutrient cycling. Practices affecting soil water content, such as tillage and crop residue management, may therefore provide opportunities for managing freeze-thaw impacts on nutrient use efficiency in crop production

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

Unraveling the mysteries of dog evolution

The increased battery of molecular markers, derived from comparative genomics, is aiding our understanding of the genetics of domestication. The recent BMC Biology article pertaining to the evolution of small size in dogs is an example of how such methods can be used to study the origin and diversification of the domestic dog. We are still challenged, however, to appreciate the genetic mechanisms responsible for the phenotypic diversity seen in 'our best friend'

Linking soil microbial community structure to potential carbon mineralization: A continental scale assessment of reduced tillage

Potential carbon mineralization (Cmin) is a commonly used indicator of soil health, with greater Cmin values interpreted as healthier soil. While Cmin values are typically greater in agricultural soils managed with minimal physical disturbance, the mechanisms driving the increases remain poorly understood. This study assessed bacterial and archaeal community structure and potential microbial drivers of Cmin in soils maintained under various degrees of physical disturbance. Potential carbon mineralization, 16S rRNA sequences, and soil characterization data were collected as part of the North American Project to Evaluate Soil Health Measurements (NAPESHM). Results showed that type of cropping system, intensity of physical disturbance, and soil pH influenced microbial sensitivity to physical disturbance. Furthermore, 28% of amplicon sequence variants (ASVs), which were important in modeling Cmin, were enriched under soils managed with minimal physical disturbance. Sequences identified as enriched under minimal disturbance and important for modeling Cmin, were linked to organisms which could produce extracellular polymeric substances and contained metabolic strategies suited for tolerating environmental stressors. Understanding how physical disturbance shapes microbial communities across climates and inherent soil properties and drives changes in Cmin provides the context necessary to evaluate management impacts on standardized measures of soil microbial activity

A Modified Molybdenum Blue Method for Orthophosphate Determination Suitable for Investigating Enzymatic Hydrolysis of Organic Phosphates

In characterizing organic phosphorus (Po) by phosphatase hydrolysis, the quantity of hydrolyzable Po is represented by the difference in orthophosphate [i.e., inorganic P (Pi)] determined after and prior to enzymatic incubation. Therefore, precise determination of Pi is of major importance for accurate application of the enzymatic hydrolysis approach. The strong acid conditions required for conventional molybdenum blue methods interferes with Pi determination due to rapid hydrolysis of labile Po and precipitation of enzymes (proteins). The molybdenum blue method of Dick and Tabatabai in 1977 reduced errors pertaining to nonenzymatic hydrolysis of Po. This study revisited the method, finding that the absorption coefficient at 850 nm was 45–49% higher than at 700 nm, and linear up to at least 80 nmol Pi in 1-mL assay solution. Therefore, adaptation of the readings at 850 nm improved the sensitivities of Pi determination by about 45%. Enzyme precipitation during Pi determination was prevented by addition of 2% sodium dodecyl sulfate (SDS) before color-forming reagents were added. This method modification provides increased sensitivity for Pi determination, thereby improving the accuracy of Po analysis by phosphatase hydrolysis

Effect of Drying on Phosphorus Distribution in Poultry Manure

Laboratory drying may alter manure phosphorus (P) distribution. The effects of freeze, air (22 °C), and oven (65 °C) drying on sequentially fractioned poultry manure P were examined. Higher drying temperatures resulted in lower percentage of dry matter. Increased H2O- and decreased sodium bicarbonate (NaHCO3)-extractable P with drying provided evidence that drying increases poultry manure P solubility. Labile fractions were predominantly inorganic P (Pi), whereas sodium hydroxide (NaOH) and hydrochloric acid (HCl) fractions had significant amounts of organic P (Po). Drying altered H2O- and NaHCO3-extractable Pi but had no consistent effect on Po in these fractions. This work suggests that variations due to drying should be taken into consideration when evaluating manures for P availability or when comparing data in which different drying methods have been utilized

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, 1M hydrochloric acid (HCl), 0.1M sodium acetate (NaOAc, pH5.0) with or without 0.05M ethylenediaminetetraacetate (EDTA), and 0.25M or 0.5M sodium hydroxide (NaOH)–0.05M EDTA. Extracts were diluted (1/10–1/150) and adjusted to pH5.0 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

Potato Growth and Yield Characteristics under Different Cropping System Management Strategies in Northeastern U.S.

Cropping systems and management practices that improve soil health may greatly enhance crop productivity. Four different potato cropping systems designed to address specific management goals of soil conservation (SC), soil improvement (SI), disease suppression (DS), and a status quo (SQ) standard rotation, along with a non-rotation (PP) control, were evaluated for their effects on potato crop growth, nutrient, and yield characteristics under both irrigated and non-irrigated (rainfed) conditions in field trials in Maine, USA, from 2004 to 2010. Both cropping system and irrigation significantly (p < 0.05) affected most potato crop parameters associated with growth and yield. All rotations increased tuber yield relative to the non-rotation PP control, and the SI system, which included yearly compost amendments, resulted in overall higher yields and a higher percentage of large-size tubers than all other systems with no irrigation (increases of 14 to 90%). DS, which contained disease-suppressive green manures and cover crops, produced the highest yields overall under irrigation (increases of 11 to 35%). Irrigation increased tuber yields in all cropping systems except SI (average increase of 27–37%). SI also resulted in significant increases in leaf area duration and chlorophyll content (as indicators of photosynthetic potential) and root and shoot biomass relative to other cropping systems, particularly under non-irrigated conditions. SI also resulted in higher shoot and tuber tissue concentrations of N, P, and K, but not most micronutrients. Overall, cropping systems that incorporate management practices such as increased rotation length and the use of cover crops, green manures, reduced tillage, and particularly, organic amendments, can substantially improve potato crop growth and yield. Irrigation also substantially increased growth and yield under normal field conditions in Maine, but SI, with its large organic amendments, was essentially a substitute for irrigation, producing comparable results without irrigation