are many reasons for this, among them the development of effective fertilizers and pesticides, government poli-In the USA, the corn (Zea mays L.)-soybean [Glycine max (L.) cies, and favorable economics. Interest in developingMerr.] rotation depends on high levels of external inputs. Few research data exist comparing conventional production practices with practices alternatives to the present agricultural system has arisen involving reduced external inputs and expanded rotations. Two trials from a number of environmental, economic, and social initiated in 1989 near Lamberton, MN, evaluated a 2-yr corn-soybean issues, including heightened concern over water quality, rotation and a 4-yr corn-soybean-oat (Avena sativa L.)/alfalfa (Medincreased reliance on government subsidies, and a conicago sativa L.)-alfalfa rotation under four management strategies. tinued decline in rural populations. The four management strategies were zero (ZI), low (LI), high (HI), Agricultural productivity gains since the 1950s reand organic (OI) inputs. One trial (V1) was on land with a history sulted from the development of farming systems that of no fertilizer and pesticide usage. The other trial (V2) was on land rely heavily on external inputs of energy and chemicals with a history of conventional fertilizer and pesticide usage. From to replace management and on-farm resources (Oberle, 1993 through 1999, average corn yield in the 2-yr HI strategy was 1994). Continuous rotation of corn and soybean cannot 8.96 Mg ha Ϫ1 in V1 and 8.72 Mg ha Ϫ1 in V2. Corn yield in the 4-yr HI strategy was 4% less than in the 2-yr HI strategy in V1, whereas be sustained without substantial additions of fertilizer in V2, the yields were not different. Soybean yield in the 2-yr HI and pesticides (Heichel, 1978; Pimentel et al., 1978). A strategy was 2.90 Mg ha Ϫ1 in V1 and 2.74 Mg ha Ϫ1 in V2. Soybean number of research studies have been conducted comyield in the 4-yr compared with the 2-yr HI strategy was 3% greaterparing conventional corn-soybean production systems in V1 and 6% greater in V2. These results suggest soybean was more with low-input and organic production systems, includresponsive than corn to the expanded rotation length in the HI strating those by Chase and Duffy (1991) and Karlen et al. (1995) in Iowa, Munn et al. (1998) in Ohio, Liebhardt strategy was 9% less in V1 and 7% less in V2 while soybean yield in et al. (1989) in Pennsylvania, Smolik and Dobbs (1991) the 4-yr OI strategy compared with the 2-yr HI strategy was 19% less and Smolik et al. (1995) in South Dakota, and Posner in V1 and 16% less in V2. These results suggest that yield of organically et al. (1995) and Mallory et al. (1998) in Wisconsin. produced soybean was reduced to a greater extent than that of organically produced corn relative to conventional production practices. By egy. Corn yield in the 4-yr OI strategy compared with the 2-yr HIThe economics of organic grain and soybean production comparing yields of the 2-and 4-yr rotations for each management from several stud...
The long-term sustainability of wheat-based dryland cropping systems in the Inland Pacific Northwest (IPNW) of the United States depends on how these systems adapt to climate change. Climate models project warming with slight increases in winter precipitation but drier summers for the IPNW. These conditions combined with elevated atmospheric CO 2 , which promote crop growth and improve transpiration-use efficiency, may be beneficial for cropping systems in the IPNW and may provide regional opportunities for agricultural diversification and intensification. Crop modeling simulation under future climatic conditions showed increased wheat productivity for the IPNW for most of the century. Water use by winter wheat was projected to decrease significantly in higher and intermediate precipitation zones and increase slightly in drier locations, but with winter crops utilizing significantly more water overall than spring crops. Crop diversification with inclusion of winter crops other than wheat is a possibility depending on agronomic and economic considerations, while substitution of -017-1950-z Climatic Change (2018) 146:247-261 DOI 10.1007/s10584
Accurate carbon and water flux simulations for croplands are greatly dependent on high quality representation of management practices and meteorological conditions, which are key drivers of the surface-atmosphere exchange processes. Fourteen site-years of carbon and water fluxes were simulated using the CropSyst model over four agricultural sites in the inland Pacific Northwest (iPNW) US from October 1, 2011 to September 30, 2015. Model performance for field-scale net ecosystem exchange of CO 2 (NEE) and evapotranspiration (ET) was evaluated by comparing simulations with long-term eddy covariance measurements. The model captured the temporal variations of NEE and ET reasonably well with an overall r of 0.78 and 0.80, and a low RMSE of 1.82 g C m −2 d −1 and 0.84 mm d −1 for NEE and ET, respectively. The model slightly underestimated NEE and ET by 0.51 g C m −2 d −1 and 0.09 mm d −1 , respectively. ET simulations showed better agreement with eddy covariance measurements than NEE. The model performed much better for the sites with detailed initial conditions (e.g., SOC content) and management practice information (e.g., tillage type). The CropSyst results showed that the winter wheat fields could be annual net carbon sinks or close to neutral with the net ecosystem carbon balance (NECB) ranging from 92 to −17 g C m −2 , while the spring crop fields were net carbon sources or neutral with an annual NECB of −327 to −3 g C m −2 . Simulations for the paired tillage sites showed that the no-till site resulted in lower CO 2 emissions for the crop rotations of winter wheat-spring garbanzo, but had higher carbon loss into the atmosphere for spring canola compared to the conventional tillage site. Water budgets did not differ significantly between the two tillage systems. Winter wheat in the high-rainfall area had higher crop yields and water use efficiency but emitted larger amounts of CO 2 into the atmosphere than in the low-rainfall area. Based Chi et al.Agricultural Carbon and Water Budgets on model evaluations in this study, CropSyst appears promising as a tool to simulate field-scale carbon and water budgets and assess the effects of different management practices and local meteorological conditions for the wheat-based cropping systems in this region.
In the USA, the corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation depends on high levels of external inputs. Few research data exist comparing conventional production practices with practices involving reduced external inputs and expanded rotations. Two trials initiated in 1989 near Lamberton, MN, evaluated a 2‐yr corn–soybean rotation and a 4‐yr corn–soybean–oat (Avena sativa L.)/alfalfa (Medicago sativa L.)–alfalfa rotation under four management strategies. The four management strategies were zero (ZI), low (LI), high (HI), and organic (OI) inputs. One trial (V1) was on land with a history of no fertilizer and pesticide usage. The other trial (V2) was on land with a history of conventional fertilizer and pesticide usage. From 1993 through 1999, average corn yield in the 2‐yr HI strategy was 8.96 Mg ha−1 in V1 and 8.72 Mg ha−1 in V2. Corn yield in the 4‐yr HI strategy was 4% less than in the 2‐yr HI strategy in V1, whereas in V2, the yields were not different. Soybean yield in the 2‐yr HI strategy was 2.90 Mg ha−1 in V1 and 2.74 Mg ha−1 in V2. Soybean yield in the 4‐yr compared with the 2‐yr HI strategy was 3% greater in V1 and 6% greater in V2. These results suggest soybean was more responsive than corn to the expanded rotation length in the HI strategy. Corn yield in the 4‐yr OI strategy compared with the 2‐yr HI strategy was 9% less in V1 and 7% less in V2 while soybean yield in the 4‐yr OI strategy compared with the 2‐yr HI strategy was 19% less in V1 and 16% less in V2. These results suggest that yield of organically produced soybean was reduced to a greater extent than that of organically produced corn relative to conventional production practices. By comparing yields of the 2‐ and 4‐yr rotations for each management strategy, this research documents the beneficial yield effects of the expanded crop rotation, which can be masked by external inputs in the LI and HI treatments.
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