K. R. Islam

Land use effects on soil quality in a tropical forest ecosystem of Bangladesh.

Human population pressures upon land resources have increased the need to assess impacts of land use change on soil quality. In order to assess effects of land use changes on soil quality properties in a tropical forest ecosystem of Bangladesh, soil samples were collected from adjacent well-stocked Shorea robustanatural forest, land reforested with Acacia, grassland and cultivated land. Land use/land cover changes (degradation of natural forest and subsequent cultivation of soils) resulted in surface compaction and significant decreases in silt and clay contents, porosity and aggregate stability, N, fulvic and labile C, and microbial biomass C. Maintenance respiration rates increased in comparison to the soils under natural forest. Use of soil deterioration index showed that soil quality deteriorated significantly ( 44%) under cultivation, while in sites revegetated with fast-growing Acacia or grasses, it improved by 6‐16%. Degradation of soil quality may have resulted from increased disruption of macroaggregates, reductions in microbial biomass, and loss of labile organic matter due to fire, deforestation, tillage and accelerated erosion. Improvement in soil quality and enhanced biological activity at reforested and grassland sites demonstrated the inherent resilience of these soils once revegetated with highly adaptable and fast growing Acacia ( Acacia sp.) and grass species.

Estimating active carbon for soil quality assessment: A simplified method for laboratory and field use

A simple method of estimating changes in biologically active soil carbon (C) could help evaluate soil quality impacts of alternative management practices. Most reports of permanganate for active C determination use highly concentrated solutions (0.333 M) that are difficult to work with and tend to react with a large fraction of soil C that is not well distinguished from total organic C. We report on a highly simplified method in which dilute, slightly alkaline KMnO4 reacts with the most readily oxidizable (active) forms of soil C, converting Mn(VII) to Mn(II), and proportionally lowering absorbance of 550 nm light. The amount of soil C that reacted increased with concentration of KMnO4 used (0.01 to 0.1 M), degree of soil drying (moist fresh soil to air-dried for 24 hour) and time of shaking (1-15 minutes). Shaking of air-dry soil in a 0.02 M KMnO4 solution for 2 minutes produced consistent and management- sensitive results, both in the laboratory and with a field kit that used a hand-held colorimeter. Addition of 0.1 M CaCl2 to the permanganate reagent enhanced settling of the soil after shaking, eliminating the need for centrifugation in the field kit. Results from the laboratory and field-kit protocols were nearly identical (R 2 = 0.98), as were those from an inter-laboratory sample exchange (R 2 = 0.91). The active soil C measured by the new procedure was more sensitive to management effects than total organic C, and more closely related to biologically mediated soil properties, such as respiration, microbial biomass and aggregation, than several other measures of soil organic C.

Soil health as a predictor of lettuce productivity and quality: A case study of urban vacant lots

Urban agriculture offers a framework for local self-reliance and resilience in cities. However, there is a concern over the capacity of urban soil to provide sustainable and safe food production. We tested the effectiveness of several soil health indicators to predict food crop productivity and quality in vacant lots in a disadvantaged neighborhood in the city of Cleveland, Ohio. We defined soil health as a state of composite well being in terms of biological, chemical, and physical properties of the soil as they relate to crop productivity. Twelve city-owned vacant lots, three close to each of the four city schools, were selected for soil properties and plant growth analyses. Soil samples were analyzed for pH, moisture content (θv), soil texture, soil organic matter (SOM), active carbon (AC), ammonium (NH4-N), nitrate (NO3-N), microbial biomass N (MBN), and nematode community parameters including total (TNN), bacteria-feeding (BFN), fungal-feeding (FFN), and plant-parasitic (PPN) nematodes, number of nematode genera (NNG), and nematode food web enrichment index (EI) and structure index (SI). Lettuce was planted in the selected vacant lots and its growth was documented through measures of dry biomass, numbers of leaves/plant, and complementary subjective appearance scores related to physiological status. All measured parameters varied considerably among vacant lots except soil pH. Principal components analysis revealed that among the primary soil physical, chemical, and biological parameters, soil clay, NO3-N, MBN, SOM, AC, TNN, BFN, FFN, and PPN contributed most to the variance of the entire dataset. There were also several positive correlations among these key soil health predictor variables: AC was positively correlated with clay, SOM, MBN, TNN, BFN, FFN and PPN, and TNN was positively correlated with AC, SOM, MBN, BFN, FFN and PPN. Of the identified primary soil health indicators, only clay, SOM, and MBN positively correlated with lettuce dry biomass, which was also positively correlated with a secondary soil health indicator, the nematode food web EI. Lettuce leaf necrosis was negatively correlated with clay, AC, SOM, MBN, TNN, FFN, and PPN, and the proportion of withered leaves was negatively correlated only with SOM. It is concluded that AC, PPN, TNN, SOM, MBN, clay, and nematode food web EI can serve as important soil health indicators that have potential for predicting crop productivity and quality in urban soils. It is also concluded that lettuce can serve as an important indicator of soil health with respect to crop productivity and quality in vacant lots.

Carbaryl, 2,4-D, and Triclopyr Adsorption in Thatch-Soil Ecosystems

Thatch development in intensively managed turf sites may cause environmental concerns for greater sorption or leaching of applied chemicals in terrestrial ecosystems. To determine the adsorption potential of Carbaryl (1-Napthyl N-methylcarbamate), 2,4-D (2,4-dichloro-phenoxyacetic acid), and Triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid) in turf ecosystems, composite thatch and underlying soil samples from three- and six-year-old stands of cool-season Southshore creeping bentgrass (Agrostis palustris Huds.) and warm-season Meyer zoysiagrass (Zoysia japonica Steud.) were collected. The samples were processed and analyzed for total organic carbon (COrg); extractable (CExt), humic (CHA) and fulvic acid (CFA); anthrone reactive nonhumic carbon (ARC) fractions; and CHA and CFA associated iron (Fe) contents. Pesticide adsorption capacity (K f ) and intensity (1/n), organic carbon partition coefficient (K OC ) and Gibbs free energy change (Δ G) were calculated for thatch materials and the underlying soils using a modified batch/flow technique. Both bentgrass (BT) and zoysiagrass thatch (ZT) contained a greater concentration of CExt, CFA, CHA, and ARC than the respective soils (BS and ZS). The CExt, CFA, CHA, and ARC concentration was higher in BT compared with ZT. The BT contained a greater concentration of bound Fe in both CFA and CHA fractions than in BS, whereas ZT had more bound Fe in CHA fraction than in ZS. On average, the BT had a greater concentration of bound Fe in CExt, CFA, and CHA fractions than in the ZT. Among the pesticides, Carbaryl had higher K f and 1/n values than 2,4-D and Triclopyr for both thatch and soil. Although the K OC and Δ G values of Carbaryl were higher in both BT and ZT than in the underlying soils, the K OC and Δ G values of 2,4-D were significantly higher in BS and ZS than in the overlying thatch materials. The 2,4-D and Triclopyr had higher leaching indices (LI) than Carbaryl for both BT and ZT materials than the respective soils. The Carbaryl, however, had a higher LI for soils than for thatch materials. Averaged across thatch materials and soils, COrg accounted for 96, 85, and 84% variations in Carbaryl, 2,4-D, and Triclopyr adsorption, respectively. Among the COrg fractions, lignin followed by CFA and CHA accounted for greater adsorption of pesticides, especially Carbaryl. The concentration of CHA and CFA bound Fe did not correlate with K f and 1/n values of pesticides.

Thatch and Soil Characteristics of Cool- and Warm-Season Turfgrasses

Abstract Turfgrass thatch development is a direct consequence of an imbalance between growth and decomposition of organic residues. This study was conducted to determine the characteristics of thatch and the underlying soil in a three-year-old stand of Southshore creeping bentgrass (Agrostis palustris Huds.) and a six-year-old stand of Meyer zoysiagrass (Zoysia japonica Steud.). Intact thatch + soil cores were randomly collected from the two sites for thatch and soil bulk density and total porosity determinations. Disturbed samples of thatch and soil were processed and analyzed for total microbial biomass carbon (C); basal and specific maintenance respiration rates; total C, nitrogen (N) and hydrogen (H) contents; easily mineralizable, soluble, oxidizable and lignin C fractions, and organic matter quality. While the total microbial biomass C content and basal respiration rates were higher in thatches, the specific maintenance respiration rates were significantly lower in soils. Total, soluble, oxidizable and lignin C, and total N and H contents were significantly greater in thatches than in soils. Although the absolute amounts of soluble and oxidizable C contents were smaller in soil than in the thatch, the soluble and oxidizable C as fractions of total C were significantly lower in thatches than in soils. The bentgrass thatch contained more microbial biomass and lignin C than the zoysiagrass thatch. Both thatches had lower bulk densities and higher total porosities than the underlying soils. Spectrophotometric analyses suggested an accumulation of finer size organic matter in the bentgrass thatch than in the zoysiagrass thatch. An increase in microbial biomass and total C, but a substantial decrease in specific maintenance respiration rates, suggest that thatch development under turf may be acting as a C sink. A decline in microbial biomass and total C contents, but significant increases in specific maintenance respiration rates, suggest that soils under thatch may be serving as sources of CO2 to the troposphere. The effect was more pronounced at the zoysiagrass site than at the bentgrass site.

Does Particle Size of Clinoptilolite Zeolite Have a Role in Textural Properties? Insight through Differential Pore-Volume Distribution of Barret, Joyner, and Halenda Model

Analysis of differential pore-volume distribution (PVD) patterns of commercial clinoptilolite fractions [(<125 µ (Z8; fine), 125–250 µ (Z9; medium), and >250 µ (Z10; coarse)] has been conducted experimentally using an analyzer to measure the nitrogen (N2) adsorption isotherms. The differential PVDs of the clinoptilolite fractions were calculated from the hysteresis loop according to the adsorption and desorption curves of the Barret, Joyner, and Halenda (BJH) model. The adsorption and desorption cycles of BJH produced heterogeneous as well as dissimilar differential PVD patterns with assorted peaks. While the adsorption curve has prolonged up to 300 nm, the desorption cycle was confined up to 190-nm pore diameter only. In the adsorption cycle, all the clinoptilolite fractions displayed U-shaped curves and had a differential pore volume in the range of 3 × 10–3 to 8 × 10–3 cm3/g A° in the micropore region with a sole peak at 1.75 nm for the fine fraction (Z8). In contrast, the curves were linear in the mesoporous region for all the fractions, with the fine fraction (Z8) having the greatest differential pore volume, whereas the other two fractions were almost parallel to each other. The desorption cycle has revealed an inverted V-shape curve with no definite patterns for the microporous region. Although the adsorption cycle could ascertain the micropore region, the desorption cycle was unable to do so. It was apparent from the differential PVD of the BJH model that fraction size has a major role in determining the textural properties of clinoptilolite fractions.

Horvath-Kawazoe Model Based Evaluation of Pore Volume of Nanoporous Clinoptilolite

ABSTRACT A liquid nitrogen (N2) adsorption isotherm was employed to understand the differential pore-volume distribution (PVD) patterns of commercial Clinoptilolite (zeolite) fractions (<125 µ (Z8; fine or micro), 125–250 µ (Z9; medium) and >250 µ (Z10; coarse). The differential PVD of the fractions were calculated from the original Horvath-Kawazoe (HK) model. A full spectrum of pore volume distribution has exhibited “curves symmetric around the origin” irrespective of the Clinoptilolite fractions. However, the fractions exhibited a definite pattern of curves for each of the micro, meso and macropore region. Although, ultramicropores couldn’t be seen in any of the fractions, super micropore region exhibited uni-modal distribution curve with mono-disperse pores for all the fractions with varying pore volumes, while multimodal and tri-modal for meso and macro pore region respectively. Irrespective of the pore region, fine fraction (Z8) exhibited higher differential pore volume than other fractions. It was evident from the differential PVD that particle size has a major role in determining the textural properties of Clinoptilolite fractions.

Considering Residual Soil Mineral Nitrogen in Corn Fertilizer Recommendations in an Irrigated Mediterranean Area

ABSTRACT Management of nitrogen (N) fertilization for economic crop production in water-stressed areas relies heavily on irrigation. The objectives were to determine the depth distribution of mineral N (Nmin) at pre-plant and post-harvest seasons and assess the residual mineral N pool as a potential source of plant-available N for irrigated corn (Zea mays L.) in southern Turkey. Pre-plant and post-harvest composite soil samples were collected randomly from farmer’s fields at 0–30, 30–60 and 60–90 cm depths, respectively, analyzed for nitrate (NO3) and ammonium (NH4) concentrations, and the Nmin values were correlated with corn yields and N uptake. Results showed that substantial amounts of pre-plant (76 to 94 kg Nmin/ha) and post-harvest (70–78 kg Nmin/ha) Nmin accumulation at different soil depths. However, the Nmin did not correlate with crop yields and N uptake. Results suggested that residual Nmin could be the basis for recommending N fertilization to support crop production.