Enrique Peiró

To develop carbon farming practices, decision-makers need detailed spatial data on the soil carbon sequestration (SCS) opportunities that conventional crop and soil management creates. This study exploratorily assessed SCS capacity across agricultural land in the Valencian Community using a simple carbon balance model within a GIS framework. Within this modelling approach, maps of net primary production (NPP), land-use-derived crop harvest indices, current soil organic carbon (SOC) stocks, and NPP and SOC mineralization coefficients were combined. Results show that while NPP across Valencian croplands and grasslands ranges from 0.64 to 6.43 Mg C ha⁻¹ yr⁻¹ (mean 2.42 Mg C ha⁻¹ yr⁻¹), the actual SCS capacity is much lower, ranging from −0.04 to 1.31 Mg C ha⁻¹ yr⁻¹ (mean 0.25 Mg C ha⁻¹ yr⁻¹). Significant variation exists among land uses: rice paddies exhibit the highest SCS capacity, while olive groves present the lowest. Between 2017 and 2021, SCS in Valencian agroecosystems may have offset the sector’s greenhouse gas (GHG) emissions, primarily driven by pasture and citrus because of their large extent and moderate SCS capacity, making agriculture a net-zero emitter. However, helping achieve cross-sectoral mitigation targets will depend in part on the widespread deployment of regenerative soil management (RSM) practices. While this study identifies priority areas for RSM implementation, further research is needed to determine which specific practices are most suitable for each location to maximize SCS.

Boron (B) is an essential but narrow-range micronutrient for citrus, with toxicity risks heightened in dry regions due to potentially high-B irrigation water and limited soil leaching. ‘Forner-Alcaide 5’ (FA5) is a promising rootstock for enhancing B-tolerance of sweet orange, but it had not been sufficiently tested before this study, specifically considering soil texture. Therefore, this greenhouse study investigated the effects on B absorption and biomass buildup of irrigating navel orange seedlings (cv. Navelina) grafted onto ‘Carrizo’ citrange (CC) and FA5 rootstocks, with 0.11, 2, or 5 mg B L⁻¹ waters and grown in clay loam or sandy loam soils. The results of this complete three-factor trial revealed that leaves are the primary sink for B (24–1300 mg kg⁻¹), indicating passive, transpiration-driven uptake and limited phloem redistribution. The presumed absence of sugar alcohols, and the weak binding affinity of B to the abundant sucrose, may account for the restricted phloem mobility of B in citrus, consistent with the mechanistic interpretation proposed in this study. FA5 rootstock showed greater B tolerance, sustaining 28% higher biomass than CC at 2 mg L⁻¹ B. Plant B uptake was found to be more related to soil soluble B than adsorbed B. Interestingly, the relationship followed a diminishing-returns pattern, thereby suggesting a balancing feedback mechanism, potentially based on B-induced stomatal closure. This analytical link between irrigation B and plant accumulation offers a framework for managing B toxicity, pending field validation.