Impacts of Spatial Differences in Cultivated Land Expansion on the Matching of Agricultural Water–Soil Resources and Zonal Regulation: A Case Study of Heilongjiang Province

Whether cultivated land expansion affects the matching of water–soil resources depends on the coupling relationship between expansion locations and water resource endowments, rather than expansion itself. Taking 12 prefecture-level cities in Heilongjiang Province from 2014 to 2024 as the research area, this study incorporates effective precipitation into the accounting to establish a generalized agricultural water-resource statistical caliber. By comprehensively adopting the models of cultivated land expansion speed and intensity, the Gini coefficient, the agricultural water–soil resource matching coefficient, and land reclamation rate, this paper explores the spatial disparities of cultivated land expansion and its impacts on water–soil resource matching. Furthermore, the three-dimensional magic cube model is applied to identify zoning types for regulation. The results show that: (1) Cultivated land in Heilongjiang Province expanded by 465 km2 from 2014 to 2024. Nevertheless, the increment was highly concentrated in Heihe, Jiamusi and Harbin. The sources of newly-added cultivated land have shifted from the equal contribution of forestland and grassland to primarily forest reclamation for cultivated land expansion. (2) During the study period, the Gini coefficient of agricultural water–soil resource matching in Heilongjiang Province ranged from 0.178 to 0.210, falling within the interval of good matching. Nevertheless, such balance is fragile. Its inter-annual fluctuations are dominated by the abundance and scarcity of precipitation rather than improvements in irrigation capacity. The matching coefficients of prefecture-level cities varied between 0.131 and 0.618, presenting a spatial pattern of high values in the east and low values in the west. Jiamusi is the only prefecture-level city that achieves the synergy of high reclamation and high matching. Qiqihar and Heihe exhibit two types of mismatches, high-reclamation with low-matching, and rapid-expansion with low-matching, respectively. (3) Based on the three-dimensional combination of expansion intensity, matching coefficient and reclamation rate, the study area is classified into four zones: water–soil constraint control zone, status quo stable maintenance zone, water–soil coordination optimization zone, and cultivated land intensive quality-improvement zone. Taking water resource carrying capacity as the pre-constraint for cultivated land expansion, targeted and differentiated strategies should be implemented according to the resource combination characteristics of each zone. This study can provide references for cultivated land management and optimized allocation of agricultural water–soil resources in the black soil region.