Crop yield and soil condition under ridge and chisel-plow tillage in the northern Corn Belt, USA

Ridge tillage is a special conservation tillage method, but the long-term effect of this tillage system on crop yield and soil quality in a corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation is largely unknown in the northern Corn Belt of the USA. Our objectives were to compare crop performance and soil condition at three nitrogen-fertilizer levels under ridge tillage (RT) and conventional tillage (CT). The experiment was started in 1990 at Brookings, SD, on a Barnes clay loam (US soil taxonomy: fine-loamy, mixed Udic Haploboroll; FAO classification: Chernozem). CT included moldboard or chisel plowing, seedbed preparation with tandem disk and field cultivator, and row cultivation. Raised beds under RT were maintained using only row cultivation. Corn grain yield was significantly (p<=0.10) greater on CT than on RT. Average (11 years and three fertilizer-N rates) corn yield was 6267 kg ha-1 with RT and 6500 kg ha-1 with CT. Soybean grain yield was not significantly (p<=0.10) different between RT and CT. Average (11 years and three fertilizer-N rates) soybean yield was 1997 kg ha-1 with RT and 2058 kg ha-1 with CT. In 9 of 11 years there was a significant soybean-yield response to N-starter fertilizer. There was no significant accumulation of NO3-N in the top 3 m of soil at the end of 9 years in either tillage treatment (111 kg NO3-N ha-1 under RT and 121 kg NO3-N ha-1 under CT). Soil pH in the top 15 cm was unaffected by tillage (average pH was 6.62). In 1999, soil organic C in the top 0.2 m was significantly greater under CT (56 Mg ha-1) than under RT (52 Mg ha-1). Bulk density in the top 0.2 m was significantly greater under RT (1.52 g cm-3) than under CT (1.44 g cm-3). Tillage did not have a great effect on grain yield or soil properties. RT can protect soil from erosion because crop residues remain relatively undisturbed on the soil surface in contrast to chisel plow. In this respect, we expect RT to be more sustainable over the long term than chisel plow tillage.