Evaluasi Karakteristik Fisikokimia Tanah Andisol dan Hubungannya terhadap Produksi Tanaman Kentang (Solanum tuberosum L.) di Kabupaten Karo

Abstract

Andisol soils, which dominate the Karo Regency, have low nutrient availability and a high capacity for phosphate fixation, and these conditions often cause crops to experience nutrient deficiencies that ultimately reduce productivity. Potato production in the region varies widely because the characteristics of Andisol soils, elevations, and cropping patterns applied by farmers in each land mapping unit differ considerably. These variations lead to inconsistent crop responses to nutrients, pH, soil texture, and land management, resulting in the absence of site-specific cultivation recommendations. Therefore, this study is needed to clarify how soil characteristics and cropping patterns influence potato productivity so that more effective and sustainable land-management strategies can be developed. This study aimed to characterize the variation in physicochemical soil properties across different Land Mapping Units (SPL) in Karo Regency and to identify the soil factors that most strongly influenced potato production. The study also assessed the effects of several cropping patterns on changes in soil properties and potato yield. Ultimately, the research sought to determine the optimal combination of soil characteristics and cropping patterns to support productive and sustainable management of Andisol soils. The study was carried out across multiple SPLs in Karo Regency, which exhibit substantial agroecological diversity, including elevations ranging from 1,000 to 1,600 m above sea level, slopes of 2–35%, soil textures from sandy to predominantly silty, and cropping systems such as rotation without mulch, rotation with mulch, intercropping, monoculture, and mulched monoculture on sloping land. This research was conducted in Karo Regency and focused on land characteristics across various elevations and slope gradients for potato cultivation, based on the established Land Mapping Units. The study consisted of two main parts. n the first part, the researcher examined the soil characteristics of potato cultivation areas through the stages of preparation, data collection, and data analysis. The researcher collected primary and secondary physical data and obtained soil samples from each land unit for analysis at the Soil Laboratory of PT Socfindo. The soil characteristics were analyzed by comparing the physical environmental conditions with the growth requirements of potatoes, based on land suitability criteria and cropping patterns, to evaluate land quality and characteristics. In the second part, the researcher analyzed the influence of soil characteristics and cropping patterns on potato (Solanum tuberosum L.) production on Andisol soils in Karo Regency. This study was conducted from February to June 2023 on several potato fields representing different cropping systems, including monoculture (with and without mulch), intercropping with vegetables, and crop rotation (with and without mulch). In this stage, the researcher collected soil samples for physical and chemical analysis, while yield data were obtained from farmers’ fields. The results of the first research phase showed that the physicochemical properties of the soil in each Land Map Unit (SPL) in Karo Regency varied considerably. Andisol soils across all units exhibited moderately acidic to acidic pH values, ranging from 4.63 to 4.99 (H₂O), with high to very high organic carbon contents of 3.31–7.18%. The capacity of cation exchange was classified as very high, ranging from 28.03 to 43.19 me/100 g. The most notable variation among land units was observed in Bray II-P, which ranged from 90.97 to 231.09 mg/kg, and in base saturation, which ranged from 5.44% to 11.51%. In addition, the exchangeable cations Ca-dd and Mg-dd differed significantly, with Ca-dd ranging from 0.37 to 2.29 me/100 g and Mg-dd from 0.38 to 1.39 me/100 g. These differences reflected variations in topography, soil texture, and nutrient leaching intensity across the SPLs. Potato yields in all SPLs ranged from 17.33 to 24.67 t/ha, with the highest yield recorded in SPL 1, which had high soil moisture, Bray II-P of 204.44 mg/kg, base saturation of 11.51%, and Ca-dd of 2.29 me/100 g. Conversely, the lowest yield was found in SPL 4, characterized by Bray II-P of 182.68 mg/kg, low base saturation (5.44%), and very low Ca-dd (0.52 me/100 g). Overall, the findings indicated that potato production was strongly influenced by Bray II-P, Ca-dd, Mg-dd, base saturation, soil texture, and cation exchange capacity. Land units with higher Bray II-P, adequate Ca-dd, and relatively stable sandy textures produced higher yields than units with overly sandy textures and low base saturation. The second phase of the study analyzed various cropping patterns, including rotation without mulch, rotation with mulch, monoculture, intercropping, and rotation–mulch systems that influenced soil conditions and crop yields. The results showed that the use of mulch consistently increased soil moisture, maintained the stability of Bray II-P, and improved soil structure, particularly on sloping land. The rotation–mulch pattern produced the highest yields in almost all land units because it was able to reduce the loss of silt and organic matter due to erosion, especially on slopes ≥20%. Rotation without mulch improved Ca and Mg during the early vegetative stage, but a decline in base saturation at harvest resulted in suboptimal tuber formation. Monoculture produced the lowest yields because it caused rapid soil compaction, decreased organic matter, and reduced nutrient uptake efficiency. Intercropping generated better yields, although its effectiveness depended strongly on the type of companion crop and the degree of shading. The integrated results of both studies showed that potato production in Karo Regency was determined by a combination of factors: elevation, silty soil texture, high organic carbon content, a balanced Ca–Mg ratio, a pH approaching neutral, high Bray II-P levels, and the use of rotation–mulch cropping patterns. Accordingly, soil management strategies for mountainous Andisols needed to focus on increasing soil pH, strengthening the Ca–Mg balance, implementing soil conservation measures on sloping land, and applying mulch to maintain water stability and prevent soil structure degradation.