Mohammad Ali Mahmoodi; Molood Mirzaie; Mohammad Taaher Hossaini
Abstract
Introduction: Soil organic matter (SOM) is an important soil quality factor that affects physical, chemical and biological properties of soil. Accurate estimation of SOM variability provides critical information especially in precision agriculture. Geostatistics and geographic information system (GIS) ...
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Introduction: Soil organic matter (SOM) is an important soil quality factor that affects physical, chemical and biological properties of soil. Accurate estimation of SOM variability provides critical information especially in precision agriculture. Geostatistics and geographic information system (GIS) are powerful tools for characterizing and mapping the spatial distribution and variability of soil properties. Kriging is a basic geostatistical technique that provides the best linear unbiased estimation for a spatially dependent variable. This method will produce satisfying results if enough sample points are available. Unfortunately, laboratory measurements of the SOM are costly and time-consuming. Artificial neural network-kriging (ANNK) is another geostatistical method that extends kriging of a primary variable to the readily available auxiliary variables based on their relationship with the primary variable. This relationship is captured using an artificial neural network (ANN) model. The residuals of the model were then interpolated using kriging, and added to the prediction obtained from the ANN model. Terrain attributes, derived from digital elevation models (DEMs), are useful for estimating SOM at landscape scale. Topographic indicators including slope, aspect, elevation, and topographic wetness index may be the dominant factors affecting SOM variability in an area with same parent material and climate. Hence, these factors can be used as auxiliary variables for estimating spatial variability of SOM using ANNK. The objective of this study was to estimate SOM spatial variability using ANNK and topographic indices and assess its status in hilly areas of Ghorveh in Kurdistan province (Iran).
Materials and Methods: A total of 150 soil samples from a depth of 0-15 cm were systematically collected in a grid spaced 2 Km × 2 Km. The SOM content of soil samples was measured in the laboratory. Topographic indicators including slope, aspect, elevation, and topographic wetness index were derived from the DEM. ANN was used to predict SOM variability based on topographic index combinations. The feed-forward network consisted of an input layer, one hidden layer with sigmoid neurons, and an output layer with linear neurons. The network was trained with Levenberg-Marquardt backpropagation algorithm. According to the Kolomogrov’s theorem, the number of nodes in the hidden layer was 2n+1, in which n is the number of input neurons. The optimal subset of topographic index combinations correlating best with the SOM was selected as the best ANN model. This model was used to generate an initial SOM surface. The residuals of ANN model were interpolated using ordinary kriging (OK) and combined with the initial SOM surface to produce the final ANNK SOM surface. The SOM status map was derived from overlaying of soil texture and SOM maps in four different levels (very low, low, medium and high).
Results and Discussion: The results of ANN suggested that elevation was the most important variable determining the distribution of SOM across the landscape. Further, aspect was the other variable which had a significant influence on SOM distribution. The selected two inputs ANN model (elevation and aspect) can explain about 33% of total variance of SOM. The cross-validation results indicated that the OK and ANNK techniques can explain about 37 and 89% of total variance of SOM, respectively. The ANNK technique performed better than the OK and ANN techniques since it was able to capture most of the small variations of SOM. The resulting SOM status map indicated a low and very low SOM content in relation with soil texture in most regions surveyed (79%). Low SOM level can be attributed to the erosive processes under Mediterranean climate on hills coupled with intensive and/or inappropriate agricultural practices. Based on the results of this study, proper agronomical and environmental planning such as soil conservation strategy is highly required in this area to restore and increase the SOM content in agricultural soils, combat soil erosion and maintain soil ecological functions and productivity. The SOM replenishment can be achieved in the degraded areas (i.e., low SOM content) by adopting conservative practices such as conservation tillage or no-tillage (e.g., direct seeding), improving land use rotations with forage crops, returning crop residues to soil, growing green manure crops, and supplying the soil with proper exogenous organic matter (compost, manure, sewage sludge, etc.). Furthermore, the results highlighted the potential of ANNK in combination with GIS to provide improved distribution patterns of SOM.
Z. Sharifi; Mohammad Taaher Hossaini
Abstract
Introduction: the use of municipal solid waste (MSW) compost in agriculture as a soil conditioner is increasing day by day because of its positive effects on biological, physical, and chemical soil properties. However, some of the composts because of contamination with heavy metals and other impurities ...
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Introduction: the use of municipal solid waste (MSW) compost in agriculture as a soil conditioner is increasing day by day because of its positive effects on biological, physical, and chemical soil properties. However, some of the composts because of contamination with heavy metals and other impurities can have deleterious effects on groundwater quality, agricultural environment, food chain, plant growth and activity of soil microorganisms. Therefore, this study was conducted to investigate the physical and chemical properties, fertilizing potential and heavy metal polluting potential of two types of municipal solid waste composts with processing time between 4 to 8 years (type A) and between1 to 4 years (type B) produced in Sanandaj city with the aim of using it as an organic fertilizer.
Materials and Methods: Sanadaj city, the center of Kurdistan province, with a population of about 335,000 is located in the west of Iran. The current solid waste generation from the city is about 320 t/day, which are not separated at source of generation. About 200 t of the total produced wastes are composted using an open windrows system at the Sanandaj MSW Composting Plant, which is located in 10 km of Sanadaj-Kamiaran road and the rest are disposed at the landfill site. The compost manufactured by the composting plant has been collected around it in two different locations. The first belonges to the product of 2004-2008 (type A) and the second belonges to the product of 2009-2013 (type B). Till now, due to lack of quality information associated with these products, they have remained unused. Therefore, in this study, we sampled 3 samples composed of six subsamples (each containing 2 kg) from the products in March 2013. The samples were analyzed to determine the physical properties (including undesirable impurities, initial moisture content, particle size distribution, particle density, bulk density (ρb), porosity, and maximum water holding capacity), and the chemical properties (including organic carbon, ash content, pH and salinity) and total amounts of N, P, Ca, Mg, K, Na, Mn, Fe, Cr, Zn, Pb, Ni and Cd using standard methods.
Results and Discussion: The results showed that bulk density, ash content, and the amounts of elements based on the dry weight of compost increased with composting time, however particle size decreased. It is well known that dry bulk density increased with composting time as ash content increased and particle size decreased by decomposition, turning and screening. The decreases of particle size with composting time cause an enrichment of metals based on the dry weight of compost. It is likely due to solubilization of metals in waste by organic acid produced during the microbial decomposition of organic matter and their subsequent adsorption on finer particles due to the higher surface area and the higher ion exchangeable capacity. The evaluation of the fertilizing potential of the surveyed composts by comparing their properties with different standard sets showed that the both composts under test in this study were failed to meet the standard permissible limits with regard to glass content (on average, 21.7 times over the permissible limit), gravel content (on average, 1.4 times over the permissible limit), lead content (on average, 1.6 times over the permissible limit), and salinity content (on average, 1.4 times over the permissible limit). Furthermore, compost type B also failed to meet the standard permissible limits with regard to initial moisture content (on average, 1.4 times over the permissible limit) and ρb (0.2 gcm-3, less than permissible limit) for agricultural purposes. The results showed that excessive amount of glass impurity bigger than 2 mm, salinity and lead contents are the major problems in the use of the composts for agricultural purposes. It should be noted that according to the maximum permissible limit of lead (150-300 mg kg-1) for compost C1 quality class described by Australian standard; both the composts can be used as fertilizers or soil amendments. In order to eliminate glass impurity, remediation approaches such as fine milling and pelleting is needed to disguise the residual glasses and render it as relatively harmless. A feasible approach to eliminate these problems is probably physical fractionation of the studied composts. It allows us to assess the distribution of nutrients and contaminants values in the different physical fractions of the composts, which is useful to detect and to eliminate of the particle sizes which are the responsible for these impurities.
Conclusion: The assessment of MSW-based compost for use in agricultural soil as fertilizer or conditioner is a sustainable recycling practice owing to its nutrient content and its positive effects on soil physico-chemical properties. Thus, we evaluated the fertilizing potential of two MSW composts produced in Sanandaj city for agricultural purposes. Altogether, the results of the study showed that excessive amount of glass impurity bigger than 2 mm and salinity were the major problems in the use of the composts for agricultural purpose. As a result, the quality of the surveyed composts was not suitable for agricultural purposes without appropriate remediation of these restrictions.