Does the Deep Placement of Fertilizers Increase Potato Yields, Fertilization Efficiency and Reduce N 2 O Emissions from the Soil?

Despite the notable decline in potato cultivation areas across Poland and Europe, potatoes remain a crucial crop with diverse applications. Achieving the ambitious emission targets set by the EU for agricultural production may be easier with the practice of deep placement of slow-release fertilizers, which may increase yields and reduce greenhouse gas emissions. To examine the effect of deep placement of slow-release fertilizers on potato tuber yields, plant nutrient uptake, nutrient use efficiency, and soil N 2 O-N emissions, a two-year field experiment was conducted on loamy sand soil classified as Alblic Podzol (Ochric) soil, under temperate climate conditions prevailing in central Poland. The experiment involved a three-field rotation (potatoes, wheat, and peas), with potatoes being cultivated after peas in both years of the study. The experiment compared the effects of applying slow-release fertilizer at soil depths of 10 and 20 cm (DP10 and DP20) to fertilization with single-nutrient fertilizers applied to the soil surface (TD). The experiment utilized increasing doses of nitrogen and phosphorus, denoted as D0 (control), D1, D2, and D3, along with a standard dose of potassium across all tested fertilizer application methods. The results of this study confirmed that deep placement of slow-release fertilizers had limited effects on potato tuber yields. Deep placement of slow-release fertilizer increased plant nitrogen uptake by 2.8–13.5% compared to topdressing. Consequently, there was an improvement in nitrogen use efficiency from 29.8–75.0% on sites with fertilizer topdressing to 38.7–89.8% on sites with slow-release fertilizer deep placement. Phosphorus uptake by plants on sites with slow-release fertilizer deep placement was approximately 9.3–13.0% higher than on sites with fertilizer topdressing. This led to an enhancement in phosphorus use efficiency from about 15.1–19.5% on fertilizer topdressing sites to 19.4–25.4% on slow-release fertilizer deep placement sites. The impact of fertilizer deep placement was found to be less pronounced compared to the effects observed with increased nitrogen and phosphorus doses. The most important factors affecting tuber yield and nutrient use in potatoes were rainfall levels during the growing season. Deep fertilization did contribute to reduce soil N 2 O emissions by about 14%. However, further research involving different fertilization methods is needed to comprehensively assess the effectiveness of this practice in reducing greenhouse gas emissions.