حاصلخیزی پتاسیم در خاک های تعدادی از تاکستان های شهرستان ملایر، غرب ایران

Background and Objectives
Soil resources are being depleted of nutrients and soil potential for food production is reducing. Among the primary nutrients, potassium is an essential nutrient for productivity, and food quality and has numerous functions in the plant system. Grapes need potassium to build vine strength and sustain adequate vigor. The Jowzan Vally a rural district in Malayer county, Hamadan province, Iran was formally recognized as a Globally Important Agricultural Heritage System (GIAHS) because of its traditional grape cultivation system. Therefore the fractions of soil’s potassium and fertilizer potassium availability index (AI) in some vineyards soil of Malayer county, which is one of the important regions of grape production in the country, were carried out. This study was done to investigate the potassium fertility of the vineyard soil of Malayer county.
Methodology
Twenty topsoil (0-30 cm) samples were collected from different vineyards in Malayer county. Soils were analyzed for some physical and chemical properties. Different fractions of potassium (solution, exchangeable, non-exchangeable, and structural potassium) were determined and the mineral components of clay were assessed by X-ray Diffraction (XRD) on oriented samples. Potassium fixation and fertilizer potassium availability index (AI) were determined after the soil samples had been treated with increasing rates of potassium. Soil samples were equilibrated at field capacity condition for 21 days at 25 ± 2°C after the addition of 0, 25, 75, 225, and 675 mg potassium kg–1. To determine the fertilizer potassium availability index (AI), the linear relation between the amount of potassium added to soil and the amount of potassium extracted with ammonium acetate was determined. All experiments were run in three replicates. The correlations between soil properties and fertilizer potassium availability index (AI) with potassium fractions were determined.
Findings
The types of minerals in the studied soils were similar and mainly included illite, chlorite, palygorskite, smectite, and low amounts of vermiculite and kaolinite, but their relative amounts were different. The average solution, exchangeable, non-exchangeable, and structural potassium concentrations in soils were 52, 314, 704, and 12381 mg kg-1, respectively. There was no deficiency of potassium in the studied soils and the concentration of potassium was at the optimal level, except for soil numbers 18 and 19. A negative and significant correlation was obtained between solution potassium concentration and the percentage of calcium carbonate equivalent in soils (r= -0.53, p≤0.05). The exchangeable potassium concentration shows a significant correlation with cation exchange capacity (r=0.48, p≤0.05), and pH (r= 0.48, p≤0.05). There was a negative and significant correlation between structural potassium and calcium carbonate equivalent percentage in soils (r= -0.48, p≤0.05). After 21 days of incubation, all three fractions of potassium (solution, exchangeable, and non-exchangeable) have increased in the studied soils. The percentage increase of solution, exchangeable, and non-exchangeable potassium was between 6 to 23%, 60 to 89%, and less than 1 to 34%, respectively. A significant part of the potassium added to the soils entered the exchangeable fraction. Values of fertilizer potassium availability index (AI) ranged from 0.87 to 1.38. In 35% of soils including the Jowzan area (one of the Globally Important Agricultural Heritage Systems), potassium fixation (AI less than one) and evidence of potassium depletion were observed. The highest increase in the percentage of non-exchangeable potassium was observed in soils with fertilizer potassium availability index of less than 1. The range of increase of non-exchangeable potassium in these soils was between 7.6 and 34%. There wasn’t any correlation between the fertilizer potassium availability index and soil properties. Mineralogical results showed that in soils where potassium fixation has occurred, illite is the most abundant mineral.
Conclusion
Soil mineralogy and total potassium values showed that most of the studied soils are fertile in terms of potassium, and the weathering of potassium minerals provides the potassium needed by plants. Nevertheless, it is recommended to manage the consumption of potassium fertilizers in the vineyards where potassium fixation was observed. Also, due to the presence of potassium-fixing clay minerals in the soil, the possibility of potassium fixation in other vineyards is predicted in case of improper management. Continued potassium export without potassium supply will lead to its eventual depletion in the soil. It is also recommended to study the potassium fixation capacity in the sand and silt components of the vineyards.