Effects of organic fertilizer substitution for chemical fertilizer on tea yield and quality: A meta-analysis focusing on alkali-hydrolyzable nitrogen dynamics

Abstract

Fertilizers are critical for tea cultivation; however, consensus is lacking on the mechanisms by which organic fertilizer substitution affects yield and quality of tea leaves. Our meta-analytical investigation synthesized 211 comparative treatments across 35 published studies to systematically evaluate the impacts of organic-for-inorganic fertilizer substitution, organic fertilizer categories, and substitution ratios on multiple parameters: soil characteristics (pH, available phosphorus (AP), available potassium (AK), alkali-hydrolyzable nitrogen (AKN), soil organic carbon (SOC)) and tea metrics (yield, 100-bud weight (BW), bud density (BD), water extract (WE), caffeine, tea polyphenols (TP), free amino acids (FAA), ratio of tea polyphenols to amino acids (RPA)). The analysis further investigates correlations between edaphic factors and tea production parameters. The findings demonstrate that organic fertilizer substitution generated significant improvements: enhanced tea yield (19.8 %), BD (10.1 %), WE (3.73 %), and FAA (12.9 %), accompanied by a reduction in RPA (13.8 %). Higher organic fertilizer proportions positively correlated with FAA content but inversely affected BD and RPA. Moreover, the substitution intervention modified soil chemistry, reducing pH while augmenting AP, AK, AKN, and SOC levels (P < 0.05), with organic fertilizer proportion positively correlating with SOC accumulation. The analysis revealed significant relationships between soil nutrient status and tea characteristics: elevated AK levels corresponded with increased WE content, while enhanced AKN concentrations positively influenced multiple parameters including yield, BD, WE, and FAA content. This meta-analysis establishes that organic fertilizer substitution enhances tea production outcomes primarily through its beneficial effects on soil AKN content. Moreover, increasing in the substitution ratio can elevate FAA content, while reducing BD and RPA in tea. Our findings highlight that replacing chemical fertilizers with organic fertilizers may improve both yield and taste of tea, as well as increase the pool of SOC.