Abstract
Rising temperatures due to climate change pose challenges for temperate crops hence, understanding soil hydrothermal dynamics is critical for optimizing crop yield. This study hypothesizes that optimum soil conditions, and effective moisture conservation are necessary for high-density apple orchards with M9 dwarfing rootstocks to maximize productivity. The present research investigates the impact of two irrigation levels (100% and 85% crop evapotranspiration (ETc)) and three mulching treatments (plastic mulch, dried grass mulch, and no mulch) on high-density apple plantations within a sub-humid agro-climatic zone in Himachal Pradesh, India, evaluated over two years. The study examines how different mulches affect soil nutrient dynamics and explores the interaction between mulch types and varying irrigation levels (full and deficit) on soil fertility. Beyond soil fertility, the research also investigates the effects of mulching on soil temperature, where it was observed that grass mulch significantly reduced maximum soil temperatures by an average of 2.2 ˚C, increased minimum soil temperatures by 1.3 ˚C compared to no mulch, and improved moisture conservation. The combination of grass mulch and 100% ETc irrigation achieved the highest yield (80.8 and 83.3 Mg ha(- 1) in 2022 and 2023, respectively). However, the 85% ETc irrigation level achieved a higher water use efficiency (WUE), showing a 13.6% increase over 100% ETc in 2022 and a 12.7% increase in 2023. Deficit irrigation affected stomatal density, indicating its sensitivity to water availability. For optimal crop productivity in high-density apple orchards, using grass mulch with 100% ETc irrigation is recommended. Alternatively, 85% ETc irrigation can be used where water conservation is a priority without compromising yield and profit. These findings demonstrate that using grass mulch in combination with appropriate irrigation can improve climate resilience in high-density apple orchards by maintaining temperature stability, conserving moisture, and enhancing WUE under water-scarce conditions.