Submitted to: Soil and Tillage Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/28/2006
Publication Date: 5/18/2007
Citation: Lenssen, A.W., Waddell, J.T., Johnson, G.D., Carlson, G.R. 2007. Diversified cropping systems in semiarid montana: nitrogen use during drought. International Journal of Soil and Tillage Research. 94(2007):362-375. Interpretive Summary: Nitrogen use and nitrogen use efficiencies are important factors for sustainable and profitable annual crop production in the northern Great Plains. We conducted a field study comparing rotation field trial from 1998 through 2003 comparing nitrogen use and nitrogen use efficiency of crops in nine rotations in two tillage systems. Crops tested included spring wheat, field pea, lentil, chickpea, yellow mustard, safflower, and sunflower. All rotations included at least one spring wheat phase. Precipitation during the course of the experiment was well below normal compared to long-term precipitation received in north-central Montana. Across the nine rotations, the best performing crop following summer fallow was spring wheat. The best performing recrop was field pea. N use and NUE of lentil, chickpea, safflower, and sunflower were low. Continuous cropping rotations failed due to insufficient plant available water. Lentil, chickpea, safflower, and sunflower performed poorly during this trial, and are not adapted to drought conditions in the semiarid regions of Montana.
Technical Abstract: Improved nitrogen use efficiency would be beneficial to agroecosystem sustainability in the northern Great Plains of the USA. The most common rotation in the northern Great Plains is fallow-spring wheat. Tillage during fallow periods controls weeds, which otherwise would use substantial amounts of water and available nitrogen, decreasing the efficiency of fallow. Chemical fallow and zero tillage systems improve soil water conservation, and may improve nitrogen availability to subsequent crops. We conducted a field trial from 1998 through 2003 comparing nitrogen uptake and nitrogen use efficiency of crops in nine rotations under two tillage systems, conventional and no-till. All rotations included spring wheat, two rotations included field pea, while lentil, chickpea, yellow mustard, sunflower, and safflower were present in single rotations with wheat. Growing season precipitation was below average in 3 of 4 years, resulting in substantial drought stress to crops not following fallow. In general, rotation had a greater influence on spring wheat nitrogen accumulation and use efficiency than did tillage system. Spring wheat following fallow had substantially higher N accumulation in seed and biomass, N harvest index, and superior nitrogen use efficiency than wheat following pea, lentil, chickpea, yellow mustard, or wheat. Preplant nitrate-N varied widely among years and rotations, but overall, conventional tillage resulted in 9 kg ha-1 nitrate-N (0-60 cm) available for spring wheat production than for zero tillage. However, zero tillage spring wheat averaged more biomass N than wheat in conventional tillage. Nitrogen accumulation in pea seed was superior to that of all alternate crops and spring wheat. Chickpea, lentil, yellow mustard, safflower, and sunflower did not perform well and were not adapted to this region during periods of below average precipitation. During periods of drought, field pea and wheat following fallow had greater nitrogen use efficiency than recropped wheat or other pulse and oilseed crops.