Bioscience Evidence 2026, Vol.16, No.4, 329-344 http://bioscipublisher.com/index.php/be 336 capacity. This indicates that although potassium has a weaker direct effect on pigment accumulation than nitrogen, appropriate potassium management can still improve functional quality (Michalska et al., 2016). In purple potato production, potassium mainly affects starch accumulation, whereas phosphorus promotes the formation of flavonoids, anthocyanins, and carotenoids. Fertilization and weed-management studies have shown that complete fertilization can increase tuber phosphorus and potassium concentrations and total yield, but certain management combinations may also increase reducing sugar content, highlighting the importance of nutrient balance for both yield and processing quality (Amjadi et al., 2025). In southern Shanxi, potato rotation with summer maize or soybean combined with straw incorporation significantly increased tuber nitrogen, phosphorus, potassium, starch, vitamin C, and dry matter contents, while improving marketable tuber rate and reducing reducing sugar accumulation (Liu et al., 2026). Soil improvement systems involving compost application increased soil organic matter and nutrient availability, enhanced aggregate stability and microbial activity, and increased marketable tuber yield by 22%~28% compared with conventional systems (Larkin, 2024). Under water stress conditions, combined application of iron nanoparticles and growth-promoting yeast increased tuber weight and promoted the accumulation of chlorogenic acid and related phenolic compounds, suggesting that micronutrient and biostimulant strategies may help maintain functional quality of colored potatoes under adverse environments (Berríos et al., 2026). 5.2 Effects of irrigation and soil moisture Short-term water deficit generally reduces plant growth, yield, and tuber quality, with the vegetative growth stage and tuber initiation stage being particularly sensitive to water shortage. Under limited water availability, irrigation should therefore be prioritized before and during early tuber formation (Wagg et al., 2021). In northwestern China, irrigation amount significantly affected tuber yield, marketable tuber production, maximum tuber weight, starch content, vitamin C content, and dry matter accumulation. When irrigation levels increased from 60% ETc to 100% ETc, these parameters increased accordingly (Zhang et al., 2023). Field experiments conducted under light soil conditions showed that drip irrigation improved productivity and tuber nutritional composition, while drip irrigation combined with nitrogen fertigation resulted in higher vitamin C content and antioxidant activity in tubers (Jakubowski et al., 2024). A three-year field study further demonstrated that drip irrigation increased dry matter, starch, vitamin C, total phenolics, chlorogenic acid, and antioxidant capacity, while fertigation further enhanced vitamin C and phenolic compound accumulation (Wichrowska et al., 2021). 5.3 Effects of planting density and field management Increasing planting density generally increases tuber number per unit area and total yield; however, intensified competition among plants for light, water, and nutrients often reduces individual tuber weight (Gadana, 2021). In purple potato cultivar ‘Jinyun No. 5’, the optimized combination of basal fertilizer application and a planting density of 5.25 plants·m⁻² simultaneously increased yield, anthocyanin content, and starch content, indicating that planting density affects not only yield components but also nutritional quality in colored potatoes (Zhong et al., 2025). For mini potato and seed tuber production, relatively higher planting density is more suitable because it increases the proportion of small and medium-sized tubers and improves seed tuber grading efficiency. A planting arrangement of 40 cm × 20 cm combined with 50% recommended fertilizer dosage achieved better economic benefits for seed tuber production (Dhangrah et al., 2024). For large fresh-market tuber production, lower or moderate planting density is preferable because it promotes larger tuber size, higher individual tuber weight, and improved yield components. For processing raw materials, moderate planting density is generally more appropriate because optimized density combined with balanced fertilization improves tuber size, market quality, and starch accumulation, whereas excessive density may reduce compositional stability. Ridging and earthing-up are considered important field management practices for maintaining potato yield and quality. In semi-arid northwestern China, plastic film mulching combined with ridge planting increased tuber yield
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