# Carbon, Water, and Light Use Efficiency Under Conservation Practice on Sloped Arable Land
## 1 Introduction  
Agroecosystems cover approximately 30% of the Earth's surface [1] and provide essential ecosystem services related to the cycling of elements, water, and carbon [2, 3]. The environmental impact of these systems is largely determined by the agricultural practices employed [4]. Conventional farming techniques, although productive, are highly resource-intensive and contribute to soil degradation, loss of organic matter, compaction, erosion, and biodiversity decline. Climate change further amplifies these issues by altering hydrological cycles, including shifts in precipitation patterns, temperature, and radiation levels [5, 6, 7, 8, 9]. These factorsincrease drought and erosion risks [10], with erosion being one of the main drivers of soil degradation globally [11]. Climate projections suggest intensified water erosion across various future scenarios [12]. The interconnection between carbon and water cycles is central to agroecosystem functioning [13], with plant transpiration accounting for roughly 60% of terrestrial evapotranspiration [14], second only to precipitation [15]. Meanwhile, photosynthesis is the primary flux of the carbon cycle. These processes are often modeled together through stomatal conductance, linking evapotranspiration and carbon assimilation [16; 17]. Water use efficiency (WUE), defined as the biomass produced per unit of water used, serves as a key indicator of these linkages [18]. Resource use efficiency--including water, nutrients, light, and carbon--is critical in agricultural systems [19; 20]. However, rising temperatures and atmospheric CO\({}_{2}\), along with reduced water availability, increasingly challenge these efficiencies [21; 22; 23; 24]. Some studies suggest that under certain conditions, agroecosystems can adjust to maintain or even improve resource use efficiency [25; 26]. Agricultural practices have a profound impact on resource efficiency [27], and the development of integrated indicators is vital for sustainable production [28]. Conservation tillage, for instance, has shown promise in improving soil structure, yield, and WUE [29]. Carbon dynamics in agroecosystems are also heavily influenced by management strategies and local environmental conditions [30; 31]. Because of this complexity, multi-year measurements across diverse landscapes are essential. Plant production not only regulates the input of organic matter formed during the photosynthetic process into the soil but also plays a crucial role in reducing atmospheric carbon levels through sequestration. This process is a key factor in mitigating global warming [32; 33]. Understanding the efficiency of resource use in agricultural systems is essential for optimizing productivity while minimizing environmental impacts. Light use efficiency (LUE), WUE, and carbon use efficiency (CUE) are commonly analyzed at the ecosystem level, but there remains a lack of studies examining these indicators in different cropping systems, particularly in relation to conservation practices. Most of the previous research has focused on flat or less erosion-prone terrains and has emphasized yield, soil quality, and carbon sequestration outcomes. However, such settings often underestimate the compounded impact of water and soil losses found in sloped landscapes. Given the increased vulnerability of sloping terrain to erosion and runoff, understanding how cover cropping and reduced tillage affect resource use efficiencies in such settings is both timely and necessary. This study addresses this gap by examining a wheat-maize rotation system under conservation agriculture on sloped arable land. It evaluates how cover crops and minimum tillage influence key components of the carbon balance, along with water, light, and carbon use efficiencies. In doing so, it also contrasts these findings with established results from flatter landscapes, adding a comparative dimension to the analysis.