In Situ Bioremediation and Crop Growth Promotion Using Trichoderma Microbial Inoculant (TMI) Ameliorate the Effects of Cu Contamination in Lowland Rice Paddies

Abstract

Soil contamination from mine tailings has impoverished the farming community of Mogpog, Marinduque, Philippines. Crop productivity has dwindled due to heavy metal (HM) contamination so the farmers’ incomes have consequently diminished. To help alleviate the constraints to crop productivity, a rice paddy experiment was conducted during the 2020 wet season in Mogpog, Marinduque to test the efficacy of using rice straw compost (RSC) and Trichoderma microbial inoculant (TMI) in increasing the yield and reducing the levels of soil copper and lead. The initial soil Cu content in the area was 379–512 mg kg−1, whereas the mean Pb concentration was 42 mg kg−1. Three treatments with three replicates each in a randomized complete block design were made: T0 (control), T1 (with RSC), and T2 (RSC + TMI). RSC was applied at 0.18 kg m−2. Mineral fertilizers were applied to all treatments at mean rates of 27.3 g m−2 for N and 16.17 g m−2 each for P and K fertilizers. After harvest, Cu, Pb, pH, organic matter (OM), and yield were measured. Data analysis showed that soil Cu levels had a significant, moderately negative correlation with yield. The combination of RSC and TMI in T2 significantly increased yield compared to the other treatments. Mean soil Cu and Pb concentrations in T2 were significantly lower than those in T1 and T0, respectively. Thus, using TMI together with RSC had a significant impact on yield accompanied by a reduction of total soil Cu and Pb concentrations. Possibly, TMI + RSC bioremediation and growth-promotion effects synergistically combined to produce large yield responses and remediation of HM in the soil, as discussed in the paper. Furthermore, rice grains harvested from these paddies have Cu content within the allowable limit for the element, whereas Pb was undetected in the rice grains.