Optimizing inorganic nitrogen extraction method to evaluate alternative cropping strategies

Abstract

Nitrogen (N) is essential for all land plants, but crops use only ∼50% of the fertilizer N, the rest being lost to the environment. Accurate estimation of soil N and optimizing N fertilizer management are critical for enhancing agricultural sustainability and profitability. This study compared the performance of five extraction methods: distilled water (DW) at room temperature (25°C), and 1 and 2 M potassium chloride (KCl) extractions conducted either cold (25°C) or hot (100°C for 4 h) to evaluate their performance in estimating inorganic N. The most practical methods identified through this comparison were then used to assess inorganic N responses to eight cover crop treatments, including single species, binary mixtures, and multispecies combinations with two compost levels (0 and 16.8 Mg ha⁻¹) in a semiarid agroecosystem. Results revealed that all KCl-based methods extracted significantly more inorganic N than DW. In January samples (before compost application), no difference was observed between 1 M cold and hot KCl. However, during the July sampling, 1 M hot KCl extracted significantly more inorganic N, ranging from 25% to 440% higher than 1 M cold KCl in compost-amended soils. No significant differences were observed among cover crop treatments. While 1 M cold KCl remained effective in early season, 1 M hot KCl better captured compost-enhanced N availability later. Compost consistently improved inorganic N, underscoring its role in nutrient management. Tailoring extraction methods to management practice and seasonal timing can enhance N assessment and support sustainable nutrient management.