Mingchu Zhang

Spectroscopic Characteristics and Biodegradability of Cold and Hot Water–Extractable Soil Organic Matter under Different Land Uses in Subarctic Alaska

Cold (22 oC) and hot water (80 oC) extractions have been used to estimate labile organic carbon (C) and nitrogen (N) in soils. Sequentially extracted cold and hot water organic matter (WEOM) from 14 Alaskan soils under different land uses were characterized by ultraviolet and fluorescence spectroscopies. Compared to cold WEOM, the ultraviolet (UV) absorptivity at 254 nm and fluorescence index were significantly (P < 0.05) decreased in hot WEOM of all soils. The biodegradability, assessed in a 21-d solution incubation, of hot WEOC and WEON was significantly (P < 0.05) greater than that of cold WEOC and WEON in all soils. The biodegradability of cold or hot WEOC was correlated with the protein-like component, indicating that a protein-like fluorophore is a labile fraction in both cold and hot WEOM pools. Information derived from this work contributed to better understanding of subarctic soil WEOM properties and their biodegradability.

Characteristics of Soil Water-Soluble Organic C and N Under Different Land Uses in Alaska

Abstract Land use conversion induces quantitative change of soil water-soluble organic matter (WSOM), but knowledge of such change is still limited. In this study, field moist and air-dried soils sampled from subarctic Alaska under three land use managements (i.e., forest, agriculture, and grassland converted from agricultural use and under a Conservation Reserve Program [CRP]) were extracted with deionized water and separated by filtration into different size fractions (2.5 &mgr;m, 0.45 &mgr;m, and 1 kDa). Water-soluble organic C (WSOC), water-soluble organic N, and fluorescence spectroscopy of each fraction were determined. There were few differences in quantitative data between samples from different land uses with air-dried samples, implying that air-dried samples were not suitable for characterizing the impact of soil management practices on soil WSOM. For field moist soil samples, the WSOC contents decreased in the order forest > CRP > agricultural land. Furthermore, WSOC was dominated by large (>0.45 &mgr;m) and small (<1 kDa) size molecules in CRP and forest soils, whereas small molecules predominated in agricultural soils. The WSOM of different size fractions and land use displayed three similar fluorophore components (two humic-like and a tyrosine-like), indicating that the impact of land use was mainly on the quantity, rather than on the composition, of WSOM. In conclusion, our data suggested that the long-term agricultural land use could lower the WSOM levels in soils; however, the decreasing trend could be reversed by conversion of agricultural land to grassland under conservation.

Irrigation-Induced Changes in Phosphorus Fractions of Caribou Sandy Loam Soil Under Different Potato Cropping Systems

Abstract Sequential fractionation is a common method used in evaluating the impacts of soil management practices on soil phosphorus (P) distribution. However, to our knowledge, this method has not been used in investigating the effects of irrigation on the changes in soil P fractions. In this work, we measured sequentially extracted P by deionized H2O, 0.5 M sodium bicarbonate (pH 8.5), 0.1 M sodium hydroxide (NaOH), and 1 M hydrochloric acid (HCl) in Caribou sandy loam soil samples from 10 potato fields under different 3-year crop rotations both with and without irrigation. As inorganic fertilizer was applied to these fields, irrigation and rotation management practices mainly affected the distribution of inorganic P fractions, but had no significant changes of organic P fractions. The impact of crop rotation was mainly reflected by H2O-extractable P. Irrigation had greater influence on stable or recalcitrant P in NaOH, HCl, and residual fractions. Higher levels of NaOH-extractable inorganic P were observed in soil from rainfed fields, whereas higher levels of HCl-extractable P were observed in soils under irrigated management. Our data indicate that irrigation may eventually decrease P availability and runoff potential in these potato soils over the long term because of the partial transfer of P in the sink from the active NaOH fraction to more stable HCl and residual fractions. Whereas information and knowledge derived from this study may shed some light on the transformation mechanism of soil P fractions for sustainable agricultural production, more field data from short- and long-term experiments are needed to confirm our observations.

Populations of the northern grasshopper, Melanoplus borealis (Orthoptera: Acrididae), in Alaska are rarely food limited.

ABSTRACT In some systems, grasshoppers appear to be food limited in most years, whereas in other systems top down forces, for example, predators, are more often implicated in population regulation. Sustainable strategies to manage grasshopper populations through habitat management require knowledge of the forces that regulate grasshopper populations. This experiment was undertaken to determine whether populations of Melanoplus borealis (Fieber), a common pest species in Alaska, are food-limited in Alaska. Cages were set up in a fallow field near Delta Junction, AK, in 3 yr (2007–2009). In 2007 and 2008, fertilizer was added to half the plots to increase primary production, and, in all years, cages within each plot were stocked with 0, 5, 9, or 13 fourth-instar M. borealis (equivalent to 0, 20, 36, or 52 grasshoppers/m2). Grasshoppers in each cage were counted weekly. Near the end of the growing season, surviving female grasshoppers (≈40% of the original number) were collected. Femur length was taken as a measure of adult size, and functional ovarioles were counted as a measure of current fecundity. If the grasshoppers were food limited, we expected to see significant effects of either density or fertilizer on grasshopper survival, size, or fecundity. The fertilizer treatment greatly increased primary production in both years. Neither fertilizer treatment nor grasshopper density had consistent effects on survival, size, or potential fecundity, leading us to conclude that food is seldom limiting to populations in the interior of Alaska at densities <50 m-2.

Soil quality under different land uses in a subarctic environment in Alaska

As the demand for food, feed, fiber, and, most recently, bio-energy increases, more land may be converted from native conditions for arable uses. Our objective was to evaluate soil quality under native forest, arable land being used for continuous barley (Hordeum valgare L.) production and land that had been tilled and subsequently enrolled in the Conservation Reserve Program (CRP) for at least 18 years. Several physical, chemical, and biological soil quality indicators were measured and a soil deterioration index (DI) was calculated using forest soil as the reference. Results indicated that most organic matter under forest resided on soil surface and was not mixed with mineral soil due to lack of activities by large soil fauna (e.g., earthworms). Soil samples from disturbed areas had a higher organic matter content, which caused most soil quality indicators to be considered ‘improved’ and resulted in better DIs for agricultural and CRP land than for forest soils. This study emphasized the importance of choosing an appropriate reference point for soil quality assessments, especially when data representing one or more key soil processes are missing.

RESPONSE OF TURFGRASS GROWTH IN A BLACK CHERNOZEMIC SOIL AMENDED WITH MUNICIPAL SOLID/BIOSOLID WASTE COMPOST

High transportation cost is a barrier which prevents land application of compost far away from where the compost is produced. As a result, use of compost in lawns is becoming a popular alternative in municipalities where compost is produced from municipal solid/biosolid waste. A four-year (2002 to 2005) field experiment was conducted on turfgrass [20% Kentucky Blue (Poa pratensis L.) + 80% Creeping Red Fescues (Festuca rubra L.)] grown on a Black Chernozem soil near Edmonton, Alberta, Canada, to determine the effect of rate and frequency of spring application of compost (prepared from soild/biosolid waste of city of Edmonton) on biomass, sward color, concentration and uptake of nutrients of sward, and soil chemical properties. There were three compost treatments: 50 Mg ha−1 annual; 100 Mg ha−1 (1st year) + 50 Mg ha−1 (2nd year) split, and 150 Mg ha−1 once in three years (2002, 2003 and 2004) applications. In addition, there were check (no fertilizers or compost) and annual nitrogen-phosphorus-potassium-sulfur (NPKS) fertilizer application (100 kg N + 20 kg P + 42 kg K + 20 kg S ha−1 annual) treatments. In the fourth year (2005), residual effect of applied compost on turfgrass growth was determined. Annual application of compost at 50 Mg ha−1 had more green color of leaf, and higher sward N concentration and biomass production of turfgrass for prolonged periods than the check treatment. In comparison with annual application, high initial compost and split applications generated greater turfgrass growth only in the first two years, but produced higher cumulative biomass over the three- or four-year period. Both annual and cumulative biomass yields were highest in treatments receiving NPKS fertilizers. After four growing seasons, there was no residual mineral N in soil from both compost and NPKS fertilizer, and no residual sulfate-S in soil from NPKS fertilizer treatments. The amounts of extractable P and exchangeable K in soil were greater in compost treatments than in the NPKS fertilizer treatment. There was downward movement of extractable P into the 15–30 cm soil depth in one-time initial and split compost and NPKS fertilizer treatments, and of sulfate-S in all compost treatments. In conclusion, annual application of compost in spring at 50 Mg ha−1 is recommended for sustainable color and growth of turfgrass.

Soil properties and barley yield under a twenty-years experiment of tillage, straw management and nitrogen application rate in the sub-arctic area of Alaska

Abstract A tillage and straw management study was started near Delta Junction Alaska (64°49′N, 147°52′W) USA in 1983 to determine the impact of tillage, straw management, and nitrogen fertilizer application rate on soil properties and barley (Hordeum vulgare L.) grain yield. In October 2003, soil samples were collected from the 0–5, 5–10, 10–25 cm depths in the treatments: no tillage (NT); disked once each spring (DO); disked twice (each for spring and fall, respectively) (DT); straw and stubble retention (SS); straw and stubble removal (NSS); and 11 and 131 kg N ha−1 nitrogen fertilizer application rates, to determine soil total nitrogen and carbon concentration, cation exchange capacity, mineral N, Mehlich-3 extractable phosphorus, exchangeable potassium, pH, electrical conductivity and bulk density. From 1983 to 2003 grain yield was measured from each treatment except in those years in which yield was lost due to birds, weeds, or chemical fallow. The no-tillage treatment tended to increase soil total organic C and N concentrations at 0–5 cm depths. Soil bulk density (0–5 cm) was lower with NT (p<0.05) than with DT. Retaining straw (SS) on the soil surface increased soil organic C concentration at 5–10 cm depth (p=0.06). Mineral N concentration in soil was higher with NT at 0–5 cm depth (p=0.05). Barley grain yield of NT was better than that of DT but varied with time. Rate of N application increased grain yield up to 91 kg N ha−1. Overall, the no-tillage and straw management had impact on some surface soil properties in sub-arctic Alaska, and no-tillage and minimum tillage increased barley crop yield.

Evapotranspiration Cycles in a High Latitude Agroecosystem: Potential Warming Role.

As the acreages of agricultural lands increase, changes in surface energetics and evapotranspiration (ET) rates may arise consequently affecting regional climate regimes. The objective of this study was to evaluate summertime ET dynamics and surface energy processes in a subarctic agricultural farm in Interior Alaska. The study includes micrometeorological and hydrological data. Results covering the period from June to September 2012 and 2013 indicated consistent energy fractions: LE/R net (67%), G/R net (6%), H/R net (27%) where LE is latent heat flux, R net is the surface net radiation, G is ground heat flux and H is the sensible heat flux. Additionally actual surface evapotranspiration from potential evaporation was found to be in the range of 59 to 66%. After comparing these rates with those of most prominent high latitude ecosystems it is argued here that if agroecosystem in high latitudes become an emerging feature in the land-use, the regional surface energy balance will significantly shift in comparison to existing Arctic natural ecosystems.

Stabilization of Erodible Slopes with Geofibers and Nontraditional Liquid Additives

An embankment was constructed with five test sections, each containing a different combination of erosion treatment methods. The objective was to provide treatments that would limit erosion until annual grasses were rooted. Treatments included combinations of geofibers with synthetic fluid or polymer emulsion. Control sections on each end of the embankment were set to provide contrast to the treated sections. A three-pronged approach was adopted to compare treatments and determine which was most effective. The first feature involved typical soil test methods for evaluating erosion at the field site. The second feature developed a methodology to determine critical shear stress for treated and untreated soils. The third feature involved construction of a laboratory-scale model of the embankment to simulate an extreme erosion environment. The results of these tests showed that more studies of the use of geofibers and nontraditional liquid additives for erosion control are warranted. While there was some discrepancy as to which of the treatments is the most effective, it is safe to say they all could be useful. Grass did not grow on the site treated with EnviroKleen, so if having grass is necessary, that product would not be recommended.

Corn and Soybean Grain Phosphorus Content Relationship with Soil Phosphorus, Phosphorus Fertilizer, and Crop Yield

Most fertilizer phosphorus (P) rate recommendations for the north-central United States are based on combination of a critical soil-test P value and a mass-balance calculation of fertilizer P required to maintain critical soil-test P. Accurate estimates of grain P removal are an essential component of P mass-balance calculation. Current north-central extension service guidelines recommend that estimates of corn and soybean grain P removal should be calculated using constant grain P concentrations. We reviewed research from the north-central region to determine the extent to which variation in grain P concentration accounts for differences in crop P removal and to determine whether predictions of grain P concentration can be improved through consideration of soil-test P, crop yield, and fertilizer P application. We found that soil-test P, grain yield, and fertilizer P are predictor variables that may significantly improve estimates of grain P concentration for corn and soybeans.