Issues with the Amendment of Post-mined Reconstituted Soil with Organic Matter for Production of Sugarcane

Abstract

The mining of heavy minerals from sand dunes along the east coast of South Africa is a controversial issue. We report a field experiment that was conducted on backfilled land at the Hillendale mine in northern KwaZulu-Natal, South Africa, to test the effect of filtercake (FC), a locally available source of organic matter, to soil and its ability to support sugarcane growth. Five treatments were evaluated including FC applied at 10, 30 and 100 Mg ha⁻¹. In two other treatments, inorganic fertilizer (IF) was applied alone (without FC) to the reconstituted soil at the recommended rate and at three times the recommended rate, as based on the fertility status of the reconstituted soil. Sugarcane was also grown in an adjacent unmined area in disturbed soil used for cropping. In agreement with fractional light interception, yield of the plant crop on the unmined area (77 Mg ha⁻¹ year⁻¹) was better than on the reconstituted soil treated with IF (59–67 Mg ha⁻¹ year⁻¹) and FC (22–39 Mg ha⁻¹ year⁻¹). Stalk length, rather than tiller number and stalk diameter, was the most important contributor to these yield differences. Based on foliar nutrient content, poor yields in all treatments could be attributed to Fe toxicity caused by oxygen deprivation in the reconstituted soil. In the FC treatments, yields were worsened by N deficiency resulted from immobilization of N. These unexpected outcomes clearly have implications for the efficient rehabilitation of formerly productive agriculture land in the wake of mining locally and worldwide.