Effects of Cascara Cherry and Other Coffee Litter Mulching on Soil Properties, Photosynthesis, and Water Use Efficiency of <i>Coffea Canephora</i> Pierre ex A. Froehner cv. Reyan No.1 Seedling

Mulching cultivation with agricultural wastes is the main production pattern of coffee at present, but the effect of mulching cultivation on photosynthetic physiological processes of coffee plants is still not clear. Therefore, a randomized block design was adopted to establish a field experiment by one-year-old <i>Coffee Canephora</i> seedlings in this study. There were four types of mulch treatments, including non-mulch coffee waste (C), mulching coffee litter (L), mulching coffee cascara (cherry pericarp, P), and mulching coffee litter and cascara (LP) in this field experiment. Soil properties and microenvironment (e.g., moisture, temperature, pH, bulk density, organic matter content, alkali-hydrolyzed nitrogen content, available potassium content, and available potassium content), agronomic traits (e.g., specific leaf area, leaf area index, plant height, and relative chlorophyll content), and photosynthetic indices (e.g., photosynthesis, transpiration, respiration, stomatal conductance, intercellular CO₂ concentration, water use efficiency, and carbon use efficiency) were investigated to determine the effects of different coffee waste mulches on the photosynthetic physiology of coffee seedlings. The results show that coffee litter and cascara mulch significantly reduced soil temperature by 0.42 or 0.33 °C, respectively, and coffee litter rather than cascara mulch significantly increased the soil’s available potassium content by 46.28%, although coffee waste mulch did not affect other soil properties or microenvironment indices; coffee cascara mulching significantly increased the specific leaf area and net and gross photosynthesis of coffee by 45.46%, 78.33%, and 91.72%, respectively, but the mulching treatments did not affect stomatal conductance, transpiration, or carbon use efficiency in this study. Additionally, coffee cascara mulching increased leaf respiration and net and gross water use efficiency by 109.34%, 80.54%, and 104.95%, respectively. The coffee cascara mulching alone had the most significant positive impact on the photosynthetic index, followed by a combination of litter and cascara, litter alone, and the control treatment. The observed variations in the coffee photosynthetic index may be attributed to the reduction of soil temperature caused by mulching treatments rather than the increase in soil nutrients content. These results indicate that coffee cascara mulching could effectively promote photosynthesis and the growth of coffee seedlings by improving the soil microenvironment.