China is an important domestication center of yams, and two main yam species of Dioscorea opposita and D. alata are commonly cultivated in China.  However, the differences of nutritional and medicinal characteristics between the two species and their subgroups remain unclear, which would greatly affect the resource conservation and commercial utilization of yams.  In this study, typical yam resources including the species of D. opposita (wild and cultivated Ruichang yam from southern China, and Tiegun yam from northern China) and two landraces of D. alata (Longyan yam and Anyuan yam from southern China) were selected as materials.  Nutritional traits and medicinal characteristics were determined and analyzed respectively.  The results showed that there was no significant differences in the content of most nutrients between D. opposita and D. alata, but most cultivated Ruichang yam of D. opposita showed higher levels of starch, soluble sugar, sucrose, and ascorbate in tuber than that in yam from D. alata.  Moreover, an UPLC-MS method was developed for identification and determination of medicinal characteristics in the two species.  The results showed that allantoin can be detected in all selected samples.  Cultivated Ruichang yam of D. opposita possessed the highest allantoin content among the tested materials, and was significantly different with that in Tiegun yam and D. alata. Dioscin was not detected in D. alata. Overall, there was little difference in nutritional composition between D. opposita and D. alata, but the medicinal quality of D. opposita was better than that of D. alata.  Due to the outstanding comprehensive quality, the local variety of cultivated Ruichang yam can be further developed and utilized.

Salt stress can be alleviated by straw layer burial in the soil, but little is known of the appropriate form of the straw layer for optimal regulation of soil water and salinity because of the uncontrollability of field tests.  Here, the following four straw forms with compaction thickness of 5 cm buried 40–45 deep were studied: no straw layer (CK), segmented straw (SL, 5 cm in length), straw pellet (SK), and straw powder (SF).  The three straw forms (SL, SK and SF) significantly delayed the infiltration of irrigation water down the column profile by 71.20–134.3 h relative to CK and the migration velocity of the wetting front under SF was the slowest.  It took longer for the wetting front to transcend SK than SL but shorter for it to reach the bottom of soil column after water crossed the straw layer.  Compared with CK, the average volumetric water content in the 0–40 cm soil layer increased by 6.45% under SL, 1.77% under SK and 5.39% under SF.  The desalination rates at the 0–40 and 0–100 cm soil layers increased by 5.85 and 3.76% under SL, 6.64 and 1.47% under SK and 5.97 and 4.82% under SF.  However, there was no significant difference among straw forms in the 0–40 cm soil layer.  Furthermore, the salt leaching efficiency (SLE, g mm^–1 h^–1) above the 40 cm layer under SL was 0.0097, being significantly higher than that under SF (0.0071) by 37.23%.  Salt storage under SL, SK and SF in the 40–45 cm layer accounted for 4.50, 16.92 and 7.43% of total storage in the 1-m column profile.  Cumulative evaporation under SL and SF decreased significantly by 41.20 and 49.00%, with both treatments having the most significant inhibition of salt accumulation (resalinization rate being 36.06 and 47.15% lower than CK) in the 0–40 cm soil layer.  In conclusion, the different forms of straw layers have desalting effects under high irrigation level (446 mm).  In particular, SL and SF performed better than SK in promoting deep salt leaching and inhibiting salt accumulation on the soil surface.  However, SL was simpler to implement and its SLE was higher.  Therefore, the segmented 5 cm straw can be recommended as an optimum physical form for establishing a straw layer for managing saline soils for crop production.