The chemical transformation of selenium (Se) in the topsoil, especially when regarded as low to sufficient Se (with high bioavailability) in dry arid environments, has great importance in the alkaline soils to yield Se-enriched food regionally. The Se content in the highly alkaline soil of the northwest region of China has inordinate agriculture economic potential, and such soil distribution is likely to produce Se-enriched crops with distinct features. One such large area of Zhongwei was investigated for the distribution of soil Se and its bioavailability, and the influencing chemical factors of soil total Se (T-Se) and bioavailable Se (B-Se) in the agroecosystem. The results suggested that the T-Se in Zhongwei soils (mg/kg) ranged from 0.01 to 0.55 with a mean of 0.2 ± 0.08, which was lower than the average Se distribution of both China (0.29 mg/kg) and the world (0.40 mg/kg). However, the overall B-Se proportion (16%) in T-Se was adequately higher than in other Se-rich soils. Spatial distribution depicted that the T-Se was specified as deficient in 42.6% and sufficient in 55.5% of the studied area, while Zhongning county was prominent with a higher B-Se proportion (22%) in the T-Se of Zhongwei. The influencing factors, such as pH and organic matter (OM), showed significant association with B-Se, as suggested by Pearson’s correlation and multiple linear regression (MLR). Furthermore, the vertical distribution of T-Se and B-Se was higher in agricultural soil (AS) than in natural soil (NS) and can be justified in the context of their association with OM. Based on these results, the Se-fortified crops can be yielded by practices to improve corresponding influencing chemical factors of soil, especially in dry areas.

It is difficult for ordinary rice to break the zinc-rich standard. However, employing multiple unique rice cultivar resources through biofortification of agronomic measures to achieve the target is a promising attempt. In this study, a pot experiment was conducted on seven different colored rice cultivars (GFHN 166, GFHN 168, GFHN 169, GH 1, GXHZ, GHSZ, and YXN), aiming to analyze the effect on zinc content, growth, quality, and health risk index when spraying zinc (400 g/ha) on the leaves at the heading age. The result indicated that after foliar biofortification treatment, the zinc content and the zinc accumulation of colored rice grains could reach up to 41.55 mg/kg and 2.28 mg/pot, respectively, increased by 43.92% and 65.22%. In addition, the SPAD value and grain protein content was 42.85 and 8.49%, also increased significantly by 2.15% and 2.91%, respectively. Among these, GXHZ and GHSZ could realize the zinc content of polished rice up to 69.7 mg/kg and 55.4 mg/kg, breaking through the standard of zinc-enrich rice (45 mg/kg). GXHZ plant height increased by 11.22%, and the zinc harvest index (6.44%) and zinc use efficiency (26.79%) were the highest. Meanwhile, the biofortification promoted the SPAD value of GHSZ and the protein content of GFHN 166 by 4.95% and 24.81%, respectively. Foliar-applied zinc at the heading stage is a vital practice to get better agronomic indicators, quality, and grain zinc biofortification of colored rice.