Attenuated cadmium and arsenic enrichment in rice by co-application of organic composting and chemical fertilization

Abstract

A pot experiment was conducted on arsenic (As) and cadmium (Cd) co-contaminated soil to discern the influence of varying proportions of pig manure compost (PM) vis-à-vis chemical fertilizers (NPK) on the mitigation of Cd and As absorption by rice. Our findings illustrated that by increasing the PM proportions from 25 to 100%, it manifested a statistically significant reduction in the mobilized fractions of Cd, accounting for up to 77% reduction in soil CaCl₂-Cd concentrations. Conversely, the NaHCO₃-As reactions were contingent on the distinct PM application rates. Furthermore, augmented PM application rates correlated with a substantial surge in Cd and As concentrations within the iron (Fe) and manganese (Mn) plaques, ranging from up to 116.6% and 85.9%, respectively. This led to a concomitant decline in Cd and As concentrations within the grains, up to 72.6% and 74.5%, respectively. Notably, grain concentrations of As and Cd diminished progressively with increased PM application, reaching a nadir with the 75% PM treatment. In summary, the observed mitigation in contamination is postulated to stem from the modulation of soil attributes via PM addition, which curtails Cd availability, combined with the bolstered immobilization of As and Cd by the Fe/Mn plaques.

Keywords: As and Cd co-contaminated soil; Availability; Fe/Mn plaques; Pig manure compost; Sustainable agriculture.

Fig. 1

The percentages of (a) Cd and (b) As fractions in the total Cd and total As and the concentrations of available (c) Cd and (d) As in soil under different treatments. Cd and As fractions: F1 (acid extractable fraction), F2 (reducible fraction), F3 (oxidizable fraction) and F4 (residual fraction). The error bars indicated standard deviation of three replicates. The different lower-case letters in the same figure indicated significant differences (ANOVA, P < 0.05) among different treatments. CK: control, NPK: all N is supplied by urea, 25PM: 25% of N by pig manure compost and 75% of N by urea, 50PM: 50% of N by pig manure compost and 50% of N by urea, 75PM: 75% of N by pig manure compost and 25% of N by urea, PM: all N is supplied by pig manure compost.

Fig. 2

Concentrations of (a) Fe, (b) Mn, (c) Cd and (d) As in the Fe/Mn plaque on the surface of roots of rice. Significant differences are indicated by different letters (P < 0.05). Fe, Mn, and Cd concentrations in the Fe/Mn plaque were measured using the DCB method. CK: control, NPK: all N is supplied by urea, 25PM: 25% of N by pig manure compost and 75% of N by urea, 50PM: 50% of N by pig manure compost and 50% of N by urea, 75PM: 75% of N by pig manure compost and 25% of N by urea, PM: all N is supplied by pig manure compost.

Fig. 3

Concentrations of Cd (a–d) and As (e–h) in different parts of rice plants under different organic compost dosage treatments. Significant differences were indicated by different lower-case letters (ANOVA, P < 0 0.05). NPK: all N is supplied by urea, 25PM: 25% of N by pig manure compost and 75% of N by urea, 50PM: 50% of N by pig manure compost and 50% of N by urea, 75PM: 75% of N by pig manure compost and 25% of N by urea, PM: all N is supplied by pig manure compost.

Fig. 4

A partial least squares path model describing the effects of the key factors on Cd (a) and As (b) concentrations in rice grain. The red and blue line indicate positive and negative correlations, respectively (***P < 0.001,**P < 0.01, *P < 0.05).