Objectives Triarrhena lutarioriparia straw are large in yield and rich in phosphorous (P). Naturally abandon of T. lutarioriparia straw around Dongting Lake leads to huge ecosystem pressure to the water body. We investigated the effects of fermented products of T. lutarioriparia straw on the phosphorus availability in red upland soil for the efficient use of T. lutarioriparia straw as a P resource.

Methods An incubation experiment was conducted using red upland soil. Two anaerobic ferment products of T. lutarioriparia straw, with high P content (4.23 g/kg, In1) and low P content (2.98 g/kg, In4), were used as test materials, and no straw addition was used as control (CK). During the incubation period of total 70 days, soils were destructively sampled at 7, 20, 40 and 70 days of incubation for analysis of total P, Olsen-P, pH, phosphorus fractions and enzyme activities, respectively.

Results Compared with CK, In1 addition increased soil Olsen-P content throughout the incubation, whereas In4 addition did not increase soil Olsen-P, and even significantly reduced Olsen-P at 40s of incubation. Both In1 and In4 addition increased water soluble P, but In4 decreased organic acid exchangeable P (the loosely adsorbed P) significantly. Both In1 and In4 addition enhanced soil phosphatase activity significantly, and In1 increased more than In4. Pearson correlation analysis showed that soil available P and loosely adsorbed P pools were positively (P<0.05) correlated with organic carbon content and phosphatase activity, indicating that soil P sorption properties and organic P content attributed to the availability of soil P.

Conclusions The anaerobic ferment product of T. lutarioriparia straw can be used as an alternative P source due to their efficiency in improving the availability of P in red upland soil, and the high P content in the ferment products stimulate the benefit effects significantly. Therefore, strains causing the enrichment of straw P should be chosen for the anaerobic fermentation of T. lutarioriparia straw.