Water diversion can alleviate water shortages caused by the uneven distribution of water resources.  China’s South-to-North Water Diversion Project (SNWD) is the largest water diversion project worldwide.  Based on the prefecture-level data of China’s Huang-Huai-Hai Plain from 2000 to 2020, this study employs an empirical strategy of Differences-in-Differences (DID) to analyze the impact of SNWD on agricultural production.  The results show that SNWD has significantly increased agricultural production, measured by the agricultural value added.  The estimated results of the benchmark model remain robust when the contemporaneous policy is addressed, an alternative outcome is used, subsamples are estimated, and alternative estimation techniques are employed.  This study argues that the potential impact mechanism may be that SNWD significantly increases the acreage for cash crops but reduces that for grain crops.  Heterogeneity analysis shows that in prefectures with high temperature or land potential, SNWD’s impact on agricultural value added is relatively low.  In contrast, in areas with prolonged sunshine or high slopes, SNWD’s impact on agricultural value added is relatively large.  Given the low added value of grain crops, the government should consider strengthening food security by subsidizing water supply to sustain grain production.

Study on soil phosphorus (P) fraction is an important aspect in probing the mechanisms of soil P accumulation in farmland and mitigating its losing risk to the environment. We used a sequential extraction method to evaluate the impacts of long-term fertilization and straw incorporation on inorganic, organic, and residual P (Pi, Po, and Pre) fractions in the plow layer (0–20 cm) of acidic paddy soil in southern China. The experiment comprised of six treatments: (i) no fertilizer control (CK); (ii) straw incorporation and green manure (SG); (iii) nitrogen and P fertilizer (NP); (iv) NP+SG; (v) NP+K fertilizer (NPK); and (vi) NPK+SG. The results showed that, compared to the initial total soil P content (TSP, 600 mg kg–1 in 1990), long-term (20 years) combined continuous P fertilizer and SG significantly increased P accumulation (by 13–20%) while single fertilization (39.3 kg P ha–1 yr–1) could maintain soil P status at the most. The average soil P fractions comprised of extractable Pi, Po, and Pre by 51.7, 33.4, and 14.9% in total soil P, respectively. With comparison of no fertilizer addition (CK), long-term single fertilization significantly (P<0.05) increased the accumulation of NaHCO3 –, NaOH–, and HCl– extractable Pi fractions accounting for two- to three-fold, while SG increased the accumulation of NaHCO3 – and NaOH– extractable Pi and Po accounting for 12–60%. Though the mobilization of Pre fractions was not significant (P>0.05), our data indicate that SG may partially substitute for fertilizer P input and minimizing soil P accumulation and subsequent environmental risk in the subtropical paddy soil.