Changes in carbon content of a Norfolk loamy sand after 14 years of conservation or conventional tillage

ABSTRACT:

Soil carbon (C) management is vital for sandy southeastern Coastal Plain (SCP) soils that are naturally low in C. A long-term investigation began in 1979 to determine if conservation tillage would increase the C content of a Norfolk loamy sand (Typic Kandiudult) with a cropping system that included corn (Zea mays L.), cotton (Gossypium hirsutum L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.). Plots were 60 m (196.8 ft) long and 23 m (75.5 ft) wide with five replications. Before modern conservation tillage technology was available, increasing soil C was believed to be nearly impossible under row crop production, particularly if cotton and soybean were part of the rotation. Tillage (conventional vs. conservation) was the main plot treatment. At the beginning of the experiment, C contents were not significantly different. In years 9 to 14, the mean C content of the 0- to 5-cm (0- to 2-in) depth for conservation tillage was nearly double that for conventional tillage: 12.0 vs 7.2 g kg⁻¹ (1.2 and 0.72%) (P ≤ 0.05). The r² of C content vs time over the 14 years was 0.44 for the 0- to 5-cm layer of the conservation tillage plots. The slope was 0.61 g kg⁻¹ yr⁻¹ (0.06%), and the probability that the slope was zero was < 0.001. A smaller slope increase of 0.17 g kg⁻¹ yr⁻¹ (0.017%) also existed for conservation tillage at the 5- to 10-cm (2.0- to 3.9-in) depth. The C content was not consistently different between tillage treatments below the 15-cm (5.9-in) depth. Improved equipment, management, and soil quality allowed conservation tillage plots to produce greater yields during years 9 to 14. Long-term conservation tillage of row crops appears to be a viable method of increasing the C content of sandy SCP soils even when soybean and cotton are part of the rotation.