Regional analysis of planting date and cultivar maturity recommendations that improve soybean oil yield and meal protein concentration.

Planting date and cultivar maturity group (MG) are major management factors affecting soybean [Glycine max (L.) Merr.] yield, but their effect on seed oil and protein concentration, and in particular meal protein concentration, is less understood. We quantified changes in seed oil and protein, and estimated meal protein concentration, and total oil and protein yield in response to planting date and cultivar MG ranging from 3 to 6 and across locations comprising a 8.3° range in latitude in the U.S. Midsouth. Our results show that delayed planting date and later cultivar maturity reduced oil concentration, and this was partially associated with a decrease in temperature during the seed fill phase. Thus, optimum cultivar MG recommendations to maximize total oil yield (in kg ha-1) for planting dates in May and June required relatively earlier cultivar MGs than those recommended to maximize seed yield. For planting dates in April, short-season MG 3 cultivars did not increase oil yield compared to full-season MG 4 or 5 cultivars due to a quadratic yield response to planting date at most locations. Planting date and cultivar maturity effects on seed protein concentration were not always consistent with the effects on estimated meal protein concentration after oil extraction. Meal protein concentration decreased with lower temperatures during seed fill, and when the start of seed fill occurred after August 15, but relatively short-season cultivar MGs reduced the risk of low meal protein concentration. Meal protein concentration is a trait of interest for the feed industry that would be beneficial to report in future studies evaluating genetic, management, and environmental effects on seed protein concentration.

Long-term agroecosystem research in the central Mississippi river basin: introduction, establishment, and overview.

Many challenges currently facing agriculture require long-term data on landscape-scale hydrologic responses to weather, such as from the Goodwater Creek Experimental Watershed (GCEW), located in northeastern Missouri, USA. This watershed is prone to surface runoff despite shallow slopes, as a result of a significant smectitic clay layer 30 to 50 cm deep that restricts downward flow of water and gives rise to a periodic perched water table. This paper is the first in a series that documents the database developed from GCEW. The objectives of this paper are to (i) establish the context of long-term data and the federal infrastructure that provides it, (ii) describe the GCEW/ Central Mississippi River Basin (CMRB) establishment and the geophysical and anthropogenic context, (iii) summarize in brief the collected research results published using data from within GCEW, (iv) describe the series of papers this work introduces, and (v) identify knowledge gaps and research needs. The rationale for the collection derives from converging trends in data from long-term research, integration of multiple disciplines, and increasing public awareness of increasingly larger problems. The outcome of those trends includes being selected as the CMRB site in the USDA-ARS Long-Term Agro-Ecosystem Research (LTAR) network. Research needs include quantifying watershed scale fluxes of N, P, K, sediment, and energy, accounting for fluxes involving forest, livestock, and anthropogenic sources, scaling from near-term point-scale results to increasingly long and broad scales, and considering whole-system interactions. This special section informs the scientific community about this database and provides support for its future use in research to solve natural resource problems important to US agricultural, environmental, and science policy.

Long-term agroecosystem research in the central Mississippi river basin: goodwater creek experimental watershed weather data.

Knowledge of weather, particularly precipitation, is fundamental to interpreting watershed and hydrologic processes. The long-term weather record in the Goodwater Creek Experimental Watershed (GCEW) complements hydrologic and water quality data in the region. The GCEW also is the core of the Central Mississippi River Basin (CMRB) node of the Long-Term Agroecosystem Research network. Our objectives are to (i) describe the climatological context of the GCEW and CMRB settings, (ii) document instrumentation and the data collection, quality assurance, and reduction processes; (iii) provide examples of the data obtained and descriptive statistics; and (iv) document the availability of and access methods to obtain the data from the web-based data access portal at . These objectives support an overall goal to make these long-term data available to the public for use in further analyses and modeling in support of research and public policy on watershed management.

Radiation Use Efficiency and Biomass Production in Soybean at Different Plant Population Densities.

As population density (POP) increases in a soybean [Glycine max (L.) Merr.] crop, maximum light interception (LI) occurs earlier in the season. Earlier canopy closure would be expected to increase the cumulative radiation intercepted. We hypothesized that if radiation use efficiency (RUE) was constant across a range of population densities in a nonstressful environment, then increasing POP would increase biomass at the end of the season. To test this hypothesis, we evaluated the response of total biomass produced during the season to cumulative intercepted photosynthetically active radiation (PAR) in field experiments at Fayetteville, AR, with soybean cultivars selected from Maturity Groups (MGs) 00 to IV. Additionally, from field experiments at Keiser, AR, with MG IV soybean cultivars, we assessed the response of RUE to POP. At both locations with MG IV cultivars, a late sowing date shortened the life cycle of the crop by 13 to 25 d compared with an early sowing date, resulting in less PAR accumulated. Similarly, early maturing cultivars had less time for PAR and biomass accumulation relative to later maturing cultivars. At Keiser, in three of the four environments, RUE decreased linearly by 26 to 30% as the POP increased from 7 to 135 plants m(-2). Final biomass at the end of the season, as a function of PAR accumulated from emergence to the full-seed-size stage of development, responded linearly to intercepted PAR up to approximately 400 MJ m(-2). Above 400 MJ m(-2), the response was curvilinear with little increases in biomass >700 MJ m(-2). Our data clearly indicate that RUE decreased as POP increased and that maximum biomass production in these environments was not limited by intercepted PAR.