Physicochemical properties of soil
Based on Stoke’s law, the texture was measured using the hydrometer method. The particle size analysis of the soil samples showed that the studied soil has a low proportion of clay (12.62%) and silt (7.46%) and a very high sand content (79.92%). The percentages of the fine earth have been recorded in Table 1. According to the grain size, the studied soil has a sandy texture.
Table 1: Granulometric constituents of the soil.
The contents of physicochemical elements in the soil have been analyzed and the descriptive data, for instance, the mean, maximum and minimum of all the elements, are recorded in Table 2. The analyses have shown that the soil has poor organic matter (C= 6.7 g/kg and N= 0.24 g/kg) and poor decomposition with a C/N of less than 27 (Bhuyan et al., 2021).
The lack of organic matter in this area may be explained by the intense utilization without rotation of various food crops, as confirmed in the study held by Gore et al., (2017).
It is a vital parameter that plays a leading role in crop production management, sustainable development and promoting the maximum utilization of chemical inputs. The pH value ranges from 4.85 to 6.37 in the different soil samples. The pH values indicated that the investigated soil was strong to slightly acidic in nature. Many reasons are behind the acidity of the area, including the massive use of synthesized fertilizers, pesticides and herbicides due to cotton production in that area (Nwite et al., 2022).
The electrical conductivity ranged from 0.16 to 0.25 EC (mS/m). The minimum and maximum conductance values were 0.16 and 0.25 mS/m. This research indicated that the EC values of Mansala-Kayikoro soil are free from salt according to the interpretation of the Indian Society Of Soil Science, which stipulates that the soil EC values comprised between 0 to 2 mS/m are salts-free (Yamini and Anilkumar, 2022)
. The lowest and highest values of calcium carbonate were 5 and 8, respectively, as reported in Table 2 (Sakarvadia et al., 2021).
The CEC is a valuable indicator of soil fertility, indicating the soil’s ability to hold cations in soil solution. The CEC value of soil samples was below 10, which means that the capacity of the soil to hold the cations is low (AGvise laboratory, 2021; Ross and Ketterings, 1996)
Table 2: Soil physicochemical parameters.
The main macronutrients are primary nutrients (Nitrogen, Phosphorus, Potassium and Sulphur). The contents of exchangeable bases (Ca2+, Mg2+, Na+) were also determined. In this study, the Nitrogen content in different soil samples ranged from 0.18 to 0.24%. Nitrogen excesses or deficiencies may adversely affect both plant health. Too much nitrogen can cause excessive vegetative growth and weak plant cells. The nitrogen content in analyzed soil samples is found in the optimum range, as confirmed by Baethgen and Alley that a value of around 0.15% of nitrogen would represent cultivated soils (Baethgen and Alley, 1987)
. The phosphorus levels were 22.58-27.90 Cmol/kg. The phosphorus content in Mansala-Kayikoro soils was low according to the previous studies on the phosphorus status in soil (Sharpley and Tunney, 2000)
. The minimum content of available potassium was recorded at 225 kg/ha; simultaneously, the maximum level was 260.34 kg/ha. The statistical average of the available potassium was recorded at 241.33 kg/ha, which is low to satisfy the plant’s need in terms of good productivity. The potassium content in the analyzed samples was below the required quantities for adequate production of crops (Murugan and Sivagnanam, 2022)
. Sulphur’s minimum and maximum values were recorded at 27 and 40.08 Cmol/kg (Table 3).
Table 3: Soil macronutrient and exchangeable bases (Descriptive statistical parameters).
The large amounts of exchangeable cations, such as calcium, magnesium and sodium, are major mineral constituents in most soils. Due to their importance, these elements were quantified (Table 3). Calcium was found in the range of 38.32-45 Cmol/kg. Calcium is uptaken by the plants in ionic form (Ca2+) and its deficiency causes yellowish to brownish plant leaves. This statement was confirmed in a study by Tanvi Kiran (Kiran, 2018)
. Magnesium content was also low and ranged between 58.97-70.00 Cmol/kg, which is inadequate according to the interpretation of Mg value in the soil (Wolf and Beegle, 2011)
. The total sodium in the soil ranged between 134.39 and 201.89 Cmol/kg. The sodium concentration seemed to be high; for instance, the mean of Na was recorded at 174.77 Cmol/kg, above the plant’s permissible level (Raymond and well, 2014)
. The most commonly found macronutrients in Mansala-Kayikoro soil were below the limit range. This means that the additional fertilizer and manure needed to increase the plant’s growth will be required.
Soil micronutrients status
The concentrations of micronutrients were determined and the statistics such as mean, maximum, minimum, standard deviation and range were evaluated, as indicated in Table 4. The iron content in the analyzed samples was high compared to other elements, as its concentration ranged between 200.20-409.40 ppm. The acidic condition of the area may explain this high concentration of Iron and the solubility status of ion cations in soil solution (Kakar et al., 2018).
Table 4: Micronutrients in soil.
At the same time, the copper and zinc contents were low in the investigated samples. The Copper content ranged from 43.80 to 52.23 ppm, with a mean value of 49.19 ppm, indicating its sufficiency in these soils. Nevertheless, the mean value of zinc concentration was 47.54 ppm indicating an optimum level for plant growth compared to its deficiency level fixed at 0.8 ppm (Fig 2). The acidic condition of the medium might cause the high zinc concentration in Mansala-Kayikoro soils. Similar results were also reported by Day and Aillery P that Zinc was sufficient in 32.63 ppm of the samples against the critical level of 0.80 ppm (Day and Aillery, 1988).
Fig 2: Micronutrient contents in soils.
The natural abundance of manganese in the soil is around 1000 ppm. The manganese concentration ranges from 232.48 to 295.55 ppm, with a mean of 258.66 ppm. According to the results, Manganese content was found to be above the permissible levels of 5.7 and 55 ppm (Kihara et al., 2020).
The Nickel level in soils varied from 4.89-18.12 ppm, with an average of 8.97 ppm. The deficiency level of nickel is 1.50 ppm. However, the Nickel threshold value of toxicity for plant growth is set at 50 ppm, indicating a good Nickel content in the analyzed samples (Kuraz et al., 2021).
In the studied soils, most micronutrients in Mansala-Kayikoro soil were above the limit range, such as Manganese, Iron and Nickel. However, zinc and copper were found deficient in the soil. This means that the study area needs some improvement, like the input of fertilizer and manures, to increase the plant’s growth and yield capacity.
Pearson correlation analysis of micronutrients revealed a significant relationship in Mansala-Kayikoro soils. However, a negative correlation was observed between Manganese, Iron and Copper, as shown in Table 5. The correlation in the study area soil indicated a solid and positive correlation in Zn-Fe; Cu-Fe; B-Mn; Ni-Zn; Zn-Cu and Cu-Ni; with an ‘R-value’ of .983; .505; .874; .690 and .678 respectively. This statement indicates that the same geochemical factors controlled the elements from the same source (Laniyan and Morakinyo, 2021)
. A weak and negative correlation was observed between Mn-Fe and Mn-Cu, indicating the poor availability of Mn in the study regions (Mugo et al., 2020).
Table 5: Correlation coefficient of Micronutrients in Mansala-Kayikoro soil.