Rasoul Mirkhani; A.R. Vaezi; hamed rezaei
Abstract
Introduction: Awareness of the physical, chemical and biological quality of soil in agriculture and natural resources is essential for optimal land management and achieving maximum economic productivity. Soil has various functions, including crop production ability, carbon storage, water retention, nutrient ...
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Introduction: Awareness of the physical, chemical and biological quality of soil in agriculture and natural resources is essential for optimal land management and achieving maximum economic productivity. Soil has various functions, including crop production ability, carbon storage, water retention, nutrient cycling, water filtering and etc. Thereby, the quality of soils can be taken into consideration depended on the purpose of their use. The soil quality indices are often regional; therefore, a set of indices cannot be used consistently to determine soil quality in all areas. In this study, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw), and the Additive Soil Quality Index (SQIa) were determined using the total data set (TDS) and minimum data set (MDS) and the impact of properties affecting the soil quality and the yield of irrigated wheat were investigated, in Nazarabad region. Materials and Methods: This study was carried out in 26000 hectares of Nazarabad agricultural lands, known as an area with irrigated farms in western Alborz province. The Nazarabad area was sub-divided into a network consisting of 95 squires of 1650 m × 1650 m. The surface soil (0-30 cm) was sampled from the farms located in the middle of each squire (9+5 soil samples from 95 farms) and the irrigated wheat was sampled from 32 farms. Then, soil physical properties including sand, silt, and clay percentages, soil structural stability (MWD), bulk density (BD), particle density, soil porosity (F), field capacity (FC) and permanent wilting point (PWP), available water (AW), saturated hydraulic conductivity (Ks) and soil chemical properties including salinity (EC), pH, organic matter (OM), equivalent calcium carbonate (TNV), available phosphorus )p < sub>ava(, available potassium )Kava(, sodium absorption ratio (SAR) and soil microbial respiration (SMR) were measured. Effective properties on soil quality were selected using SPSS 24 by principal component analysis method (PCA). For this purpose, components with Eigen values greater than one were selected and in each component, properties with high loading coefficient up to 10% lower than the highest loading coefficient were selected MDS affecting soil quality. Then, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw) and Additive Soil Quality Index (SQIa) were determined using TDS and MDS. For validating soil quality indices, the correlation between the yield of irrigated wheat and NQI, IQIa and IQIw indices were determined in MDS and TDS. Results and Discussion: The results showed that the correlation between the soil quality indices (NQI, SQIw and SQIa( using total data set and MDS were significant (p <0.01). In addition, a significant correlation was observed between methods of MDS and TDS in IQIw (r=0.76), IQIa (r=0.73) and NQI (r=0.68) indices. According to the results, there was a significant correlation (p <0.01) between the yield of irrigated wheat and IQIw (r=0.68), IQIa (r=0.67) and NQI (r=0.62) using MDS method; and using total data set method this correlation was 0.61, 0.58 and 0.58, respectively. The results indicated that using NQI, SQIw and SQIa indices based on MDS, 42, 57 and 57% of the study area were in very high quality category and 29, 25 and 24% were in high quality category, respectively. However, using NQI, SQIw and SQIa indices based on TDS, 16, 16 and 18% of the study area were in very high quality class and 42, 39 and 45% were in high quality class, respectively. Conclusion: The results showed that in Nazarabad region, the yield of irrigated wheat was affected by texture, p < sub>ava, B, SAR, Bd and TNV. There was no significant difference between IQIw and IQIa and NQI indices. In addition, the correlation between soil quality indices based on MDS and total data set was significant, and the correlation between the yield of irrigated wheat and the soil quality indices was stronger while using MDS rather than the use of TDS. Therefore, the use of MDS is more appropriate due to better results and fewer properties and less cost. According to the results obtained from Nazarabad region using NQI and SQIw indices, nearly 82% and 72% of the area are in the very high and high quality class, about 6% and 8% are in the moderate quality class and about 7% are in very low and low quality class, respectively. The studied area is less restricted in terms of physical properties such as soil texture and bulk density. Consequently, due to the high quality of soils in Nazarabad region, it is possible to improve the yield of wheat by proper management.
Saeed Saadat; leila esmaeelnejad; hamed rezaei; Rasoul mirkhani; javad seyedmohammadi
Abstract
Introduction: Soil aggregates refers to groups of soil particles which attach to each other stronger than neighbour particles. Aggregate stability shows the capability and strength of soil aggregates to tolerate breakup when disruptive stresses and destructive forces via mechanical agricultural operation ...
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Introduction: Soil aggregates refers to groups of soil particles which attach to each other stronger than neighbour particles. Aggregate stability shows the capability and strength of soil aggregates to tolerate breakup when disruptive stresses and destructive forces via mechanical agricultural operation such as tillage and water or wind erosion are applied. Wet aggregate stability shows how well a soil can withstand raindrop impact and water erosion, while size distribution of dry aggregates can be used to predict resistance to abrasion and wind erosion. Aggregate stability changes can act as the first indicators of recovery or degradation of soils. Aggregate stability is an indicator of organic matter content, biological activity, and nutrient cycling in soil. Generally, in small aggregates (< 0.25 mm), the particles are bound by older and more stable forms of organic matter. Microbial decomposition of fresh organic matter releases products (that are less stable) that bind small aggregates into large aggregates (> 2-5 mm). Although, there is not a unique acceptable methodology that serves and applies the entire world up to now, aggregate stability has been introduced as a soil physical quality indicator. Difficulties remain when comparison of aggregate stability from different methodologies are done. The objective of the present study was to assess appropriate and satisfactory aggregate stability tests that enable to distinguish the soil physical quality condition of both arid and moist medium textured soils.
Materials and Methods: A total of 120 soil samples which contained 60 wetland samples from Guilan province with a very humid climate, average annual rainfall of 1285 mm, and average annual temperature of 16°C, and 60 samples from Fars province with dry climate, average rainfall of 225 mm, and the average annual temperature of 27°C were provided. Soil sampling was performed from surface layer (0-20 cm). Each 10 soil samples with similar texture were mixed and one soil sample for each texture was finally obtained. After air drying and sieving, soil texture and organic carbon were determined by pipette and oxidation methods, respectively. Also, undisturbed samples were taken using metal cylinders from surface layer of 5-15 cm for determination of soil saturation coefficient, soil moisture curve, and soil bulk density. Also, in order to determine the aggregate stability, Kemper and Rosenau, de Leenheer and de Boodt, as well as Le Bissonnais were used.
Results and Discussion: Among different tested methods, wet sieving using the well known fast wetting methods of Kemper & Rosenau and of Le Bissonnais presented similar results in both climates. The mean weight diameter value of both methods for assessing aggregate stability can be considered as a dependable indicator of soil structure status for comparing soils. These aggregate stability tests were in correspondence with only one out of the eight soil physical quality indicators when the entire soils were used. It was concluded that the aggregate stability should be used judiciously and in accordance with other indicators for an overall assessing of the soil physical quality condition. The great differences in the estimation of aggregate stability between KRSW and LB2 with other methods confirm that aggregate stability increases with increasing soil moisture content. This involves reducing the amount of air condensed, which results in the reduction of compressive forces on the aggregates during rapid wetting. But the lack of similarity between the KRSW and LB2 methods in terms of MWD suggests that the results of these two methods are not comparable to dry and wet soils. The difference in aggregate size distribution from all three treatments of LB method was higher in dry areas than wet areas. Only dry soils based on LB (LB1 and LB3 treatments based on MWD) (P <0.05) are comparable. In dry soils, the LB3 method is very efficient. This method involves the use of ethanol that protects the aggregate structure against dryness stresses. The lack of similarity between the MWD and other soil quality indicators describes the complexity of the soil structure, which is dependent on the location. It seems that SOC can be considered as an indicator with high correlation with the aggregate sustainability index of LB and KRFW methods, at least in the studied medium-textured soils.
Conclusion: Since only a soil quality index (SOC) had a similar trend to the sustainability index derived from these two methods (LB1 and KRFW), it can be concluded that aggregate stability should be judged and recognized correctly, along with other used soil physical indicators for a general assessment of the conditions. In case of arid land soils, efficiency of pre-wetted methods of Kemper and Rosenau and of Le Bissonnais as well as pre-wetted Le Bissonnais with mechanical slaking and shaking were similar. If a simple and rapid analysis of the structure status is needed, single tests such as fast wetted Kemper and Rosenau and Le Bissonnais can be used.
