Core Ideas Soybean in organic no‐till yielded as well as conventional organic. Corn in organic no‐till had lower yield than conventional organic. A crimped cover crop can cause N immobilization and reduced corn yield. Organic crop production is dependent on tillage for weed control, but because tillage can lead to decreased levels of soil organic carbon (SOC) alternative management needs to be explored. This study was conducted in Boone County, Missouri, in 2012 to 2014 to determine the effects of three organic production systems and four poultry compost rates on crop yield and SOC on a claypan soil. The production systems included tillage with no cover crop, tillage with a mowed and incorporated cover crop, and no‐till with a crimped cover crop in a wheat (Triticum aestivum L.)–corn (Zea mays L.)–soybean (Glycine max L.) rotation. Cover crops included cereal rye (Secale cereale L) and hairy vetch (Vicia villosa L.). Compost rates were 0, half the recommended rate, the recommended rate, and 1.5 times the recommended rate. Achieving cover crop biomass sufficient for weed suppression was a challenge when soil fertility declined during the study. Corn yield was reduced 30% in 2013 in no‐till plots compared to tilled although plant populations were nearly equal, indicating that N immobilization may be significant in crimped cover crops. When there was adequate soil moisture and weed control from the cover crop, soybean grown under organic no‐till was competitive with tilled treatments. Optimum timing of cover crop crimping for acceptable weed control was more successful in a soybean system compared with corn. Organic no‐till in this study was more successful in soybean and wheat than in corn, when the cover crop biomass was sufficient to suppress weeds.

Maize (Zea mays L.) grain yield is considered to be highly associated with carbohydrate dynamics in leaves and developing ears during the critical period bracketing silking. Carbohydrate changes are sensitive to variation in nitrogen (N) availability, yet a comprehensive analysis of the N effect on various carbohydrate concentrations around silking remains elusive. A 2‐yr field study was conducted to investigate grain yield, N uptake, ear dry matter and carbohydrate concentrations in ear‐leaves and whole ears (prior to silking) and kernels (after silking) of maize grown with 0, 150, and 300 kg N ha−1. Greater N availability increased maize shoot dry matter and N content at silking and physiological maturity, as well as grain yield. While N had little effect on ear‐leaf glucose concentration, sucrose concentration increased but starch concentration decreased with increasing N, regardless of sampling time. Prior to silking, glucose and fructose concentrations in the developing ear responded positively to increasing N availability, but sucrose and starch concentrations declined. In growing kernels shortly after silking, glucose and fructose concentrations in N fertilized treatments were significantly lower than those in the zero‐N treatment. In contrast, a significant increase in kernel starch concentration was found in response to 300 kg N ha−1. These observations point to an important role of the carbohydrate composition of unpollinated ears prior to silking with regard to kernel set and post‐silking kernel starch accumulation, and thus final crop yield.

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Core Ideas Drought decreased the CO2 and N2O 2 out of 3 yr of the study but in a normal precipitation year, GHG emissions increased significantly for corn and wheat but stayed relatively low for soybean. Increasing compost from 1× to 1.5× the recommended rate showed no increase in N2O emissions. NTCC and 1×+ compost rates typically resulted in the greatest GWP. Organic crop production is increasing with consumer demand, but research is needed on the best management practices that minimize greenhouse gas (GHG) emissions. This study was conducted in central Missouri from 2012 to 2014 using a 3‐yr rotation, consisting of corn (Zea mays L.), cereal rye cover crop (Secale cereale L.), soybean (Glycine max L.), winter wheat (Triticum aestivum L.), summer cover crop mix [Buckwheat (Fagopyrum esculentum Moench), sunn hemp (Crotalaria juncea L.), cowpea (Vigna unguiculata (L.) Walp.)], and cereal rye/hairy vetch cover crop mix (Vicia villosa L.). Treatments included tillage/cover crop practice (TCCP) combinations: (i) tillage with no cover crop (TNCC), (ii) tillage with cover crop (TCC), and (iii) no‐till with cover crop (NTCC) and compost additions relative to the recommended rate (0×, 1×, 1.5×). Carbon dioxide (CO2) and nitrous oxide (N2O) emission measurements followed GRACEnet protocol. GHG emissions were not influenced by management practices in 2012 due to severe drought. TCCP had direct (2013 corn, 2014 soybean) or interactive (2014 wheat) effects on CO2 emissions; compost had a direct effect (2014 corn) on N2O emissions. Drought in 2012 and 2013 contributed to generally low CO2 and N2O emissions (99–2924 kg CO2–C ha−1 and 0–0.8 kg N2O–N ha−1, respectively) while emissions increased in 2014 (527–7740 kg CO2–C ha−1 and <0.1–10.1 kg N2O–N ha−1, respectively). Across all years and crops, NTCC showed greater CO2 emissions than TNCC (1579 and 893 kg CO2–C ha−1, respectively). While few treatment differences were observed, TCCP resulted in more GHG emission differences than compost rate.