# Carbon, Water, and Light Use Efficiency Under Conservation Practice on Sloped Arable Land
## 4 Discussion  
Soils today are greatly impacted by human activities such as deforestation, industrial agriculture, urbanization, and pollution. These anthropogenic pressures have led to widespread soil degradation, erosion, salinization, and desertification, thereby undermining essential ecosystem services [48]. This leads to various environmental issues, including soil degradation, loss of organic matter, compaction, intensified erosion, deterioration of soil structure, and a decline in biodiversity [49]. Among conservation measures, cover crops are increasingly recognized for their multifunctional role in improving soil health and delivering ecosystem services [50]. They reduce erosion, mitigate compaction, enhance soil structure, and increase organic carbon, microbial activity, and nutrient cycling. Despite their potential, studies remain divided on their impact on subsequent crop yields and water use efficiency (WUE) [51], with some reporting positive [52; 53] and others negative effects [54]. Minimizing tillage, early sowing, no-till practices, etc., can positively influence water use efficiency (WUE) [55]. Our results support findings that cover crops can improve subsequent crop development and resource use, particularly in erosion-prone sloping terrains--a context less frequently studied in the literature. Specifically, we observed enhanced WUE in maize after cover cropping, especially in the drier years (2022-2023), suggesting that conservation practices may stabilize yields under water-limited conditions. This is consistent with previous findings that improved water retention due to organic residues and erosion control may offset early-season moisture depletion caused by cover crops [56; 57]. However, the effect varied by crop and tillage intensity. While maize benefited significantly, wheat showed a weaker response to conservation tillage, confirming earlier studies that highlight variable responses across crop types and climates [55; 58]. Our observations underscore the need to consider crop-specific and terrain-related dynamics when evaluating conservation strategies. Regarding carbon use efficiency (CUE), our study observed no statistically significant variation across treatments or years, even under markedly different climatic conditions (wet in 2021 vs. drought in 2023). This result aligns with the earlier research indicating that CUE can remain stable despite environmental variability due to internal plant regulatory mechanisms and carbon allocation strategies that prioritize maintenance respiration under stress [45; 46; 59]. Although ecosystem-level studies have reported seasonal CUE variation in response to soil moisture and temperature [60], our findings suggest that in annual cropping systems, such as maize and wheat, this response may be buffered by management practices like residue retention and minimized tillage. The unchanged CUE across treatments may also reflect a trade-off between carbon assimilation and autotrophic respiration. Under conservation systems, improved soil conditions can support higher microbial and root activity, potentially increasing autotrophic respiration and counterbalancing gains in gross primary productivity. This supports the hypothesis that CUE stability under different agricultural practices may not indicate inefficiency but rather a dynamic equilibrium within the carbon cycle [60]. While previous research has emphasized WUE and LUE in conservation agriculture, fewer studies have incorporated CUE as a metric of resource efficiency. Our findings thus contribute new insights by showing that, even when biomass and WUE increase under conservation practices, CUE may remain stable--highlighting the importance of including all three metrics for a holistic understanding of agroecosystem functioning. CUE and WUE often respond differently to environmental changes and land management, as also shown in spatial and temporal studies [61].