Table 1.
Inputs, aquatic toxicity, yields, weed biomass, and net returns for the three cropping systems in the Marsden Farm rotation experiment, Boone Co., IA, 2006–2011a
Cropping system
Metrics: 2-year rotation: Corn-soybean 3-year rotation: Corn-soybean-oat + red clover 4-year rotation: Corn-soybean-oat + alfalfa-alfalfa 
Whole rotation: 
Mineral N fertilizer inputs, kg N ha-1 yr-1 80 a 9 b 7 b 
Herbicide inputs, kg active ingredients ha-1 yr-1 1.78 a 0.07 b 0.05 b 
Herbicide aquatic toxicity, comparative toxic units 21973 a 74 b 56 b 
Fossil energy inputs, GJ ha-1 yr-1 8.9 a 4.0 b 4.1 b 
Labor requirements, hr ha-1 yr-1 1.7 c 2.8 b 3.6 a 
Net returns to land and managementb, $ ha-1 yr-1 954 965 913 
Crop yields: 
Corn, Mg ha-1 12.3 b 12.6 a 12.9 a 
Soybean, Mg ha-1 3.4 b 3.7 a 3.8 a 
Oat, Mg ha-1 — 3.5 b 3.6 a 
Alfalfa, Mg ha-1 — — 8.9 
Weed biomass: 
In corn, kg ha-1 2.9 6.2 5.5 
In soybean, kg ha-1 0.8 2.4 2.1 
Cropping system
Metrics: 2-year rotation: Corn-soybean 3-year rotation: Corn-soybean-oat + red clover 4-year rotation: Corn-soybean-oat + alfalfa-alfalfa 
Whole rotation: 
Mineral N fertilizer inputs, kg N ha-1 yr-1 80 a 9 b 7 b 
Herbicide inputs, kg active ingredients ha-1 yr-1 1.78 a 0.07 b 0.05 b 
Herbicide aquatic toxicity, comparative toxic units 21973 a 74 b 56 b 
Fossil energy inputs, GJ ha-1 yr-1 8.9 a 4.0 b 4.1 b 
Labor requirements, hr ha-1 yr-1 1.7 c 2.8 b 3.6 a 
Net returns to land and managementb, $ ha-1 yr-1 954 965 913 
Crop yields: 
Corn, Mg ha-1 12.3 b 12.6 a 12.9 a 
Soybean, Mg ha-1 3.4 b 3.7 a 3.8 a 
Oat, Mg ha-1 — 3.5 b 3.6 a 
Alfalfa, Mg ha-1 — — 8.9 
Weed biomass: 
In corn, kg ha-1 2.9 6.2 5.5 
In soybean, kg ha-1 0.8 2.4 2.1 

aWithin rows, means followed by different letters are significantly different (P < 0.05); means not followed by letters are statistically equivalent. Data are from Davis et al. (2012).

bCrop subsidy payments were not included as sources of revenue.

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