Reclamation of an Ultisol Damaged by Mechanical Land Clearing

Mechanical land clearing in 1972 of a Yurimaguas soil (fine-loamy siliceous, isohyperthermic Typic Paleudult) located in the Amazon Basin of Peru resulted in compacted soil that was abandoned for continuous crop production in 1974. The purposes of this study were to reclaim this abandoned land for continuous cultivation and to evaluate temporal changes in soil physical properties with time after reclamation treatments began. In February 1980, guinea grass [Panicum maximum L.], which covered the compacted soil, was cut by hand, dried, and burned. The following eight reclamation treatments were imposed: (1) control (no till), planted with a planting stick; (2) rototill (12 kW) and stick planted; (3) rototill (48 kW); (4) chisel plow 25-cm deep, rototill (48 kW); (5) controlled traffic (i.e., assignment of pathways for foot traffic); (6) bedding with hoe and planted with stick; (7) simulated subsoiling to 25 cm with a tile spade; and (8) mulching (mulch applied when seedlings were 10- to 25-cm high). The following soil physical properties were quantitied several times during the study: infiltration rate, cone index (CI), bulk density (ρb), and the soil-water characteristic. The crop rotation during the 2-yr-long period was rice (Oryza sativa L.)-soybean [Glycine max (L.) Merr.]-corn (Zea mays L.)-soybean-corn-rice. Compared to the control treatment, all others decreased ρb and CI and increased infiltration rate, macro porosity, and total porosity in the 0- to 15-cm depth. Only chisel plowing and simulated subsoiling alleviated the detrimental effects of the compacted soil below 15 cm. Infiltration rate at the conclusion of the experiment for the control treatment was 9 mm h⁻¹ compared to 148 mm h⁻¹ for the chisel plow treatment. Yield responses were greater for chiseling and simulated subsoiling. For example, the average relative grain yield for each of the three crops was 100% for chiseling; for no-till, relative yields were 69, 23, and 20% for rice, soybean, and corn, respectively. We conclude that compacted soils similar to the Yurimaguas series can be reclaimed for continuous cropping by using deep tillage practices such as chisel plowing and subsoiling.