Corn is planted earlier every year and this is one important component in maximizing grain yield. In 2009, 47% of the statewide corn crop was planted by approximately April 26. This was four days earlier than the previous 5-year average (USDA NASS, 2009). Earlier planting dates are attributed to several causes: larger acreage per producer, less spring tillage, advancements in hybrids, increased tile drainage, and improved seed treatments. The start of corn planting is generally related to the date when the soil temperature reaches 50°F (10°C) or greater. Previous Iowa State University (ISU) recommendations for 99% maximum yield, relative to planting date, were identified as April 20 to May 19 statewide. We believe that this planting window can and should be earlier to achieve high yields. Research has been conducted at seven sites in Iowa since 2006. This report compiles the data and statistical results observed during this multi-year and multi-location study aiming to provide more precise planting date recommendations by region.
Variability in soil organic carbon (SOC) results from natural and human processes interacting across time and space, and leads to large variation in the minimum difference in SOC that can be detected with a particular experimental design. Here we report a unique comparison of minimum detectable differences (MDDs) in SOC, and the estimated times required to observe those MDDs across the north central United States, calculated for the two most common SOC experiments: (1) a comparison between two treatments, e.g., moldboard plow (MP) and no-tillage (NT), using a randomized complete block design experiment; and (2) a comparison of changes in SOC over time for a particular treatment, e.g., NT, using a randomized complete block design experiment with time as an additional factor. We estimated the duration of the two experiment types required to achieve MDD through simulation of SOC dynamics. Data for the study came from 13 experimental sites located in Iowa, Illinois, Ohio, Michigan, Wisconsin, Missouri, and Minnesota. Soil organic carbon, bulk density, and texture were measured at four soil depths. Minimum detectable differences were calculated with probability of Type I error of 0.05 and probability of Type II error of 0.15.The MDDs in SOC were highly variable across the region and increased with soil depth. At 0 to 10 cm (0 to 3.9 in) soil depth, MDDs with five replications ranged from 1.04 g C kg -1 (0.017 oz C lb ; 3%) to 3.12 g C kg -1 (0.050 oz C lb -1 ; 13%) for SOC change over time. Large differences were also predicted in the experiment duration required to detect a difference in SOC between MP and NT (from 8 to >100 years with five replications), or a change in SOC over time under NT management (from 11 to 71 years with five replications). At most locations, the time required to detect a change in SOC under NT was shorter than the time required to detect a difference between MP and NT. Minimum detectable difference and experiment duration decreased with the number of replications and were correlated with SOC variability and soil texture of the experimental sites, i.e., they tended to be lower in fine textured soils. Experiment duration was also reduced by increased crop productivity and the amount of residue left on the soil. The relationships and methods described here enable the design of experiments with high power of detecting differences and changes in SOC and enhance our understanding of how management practices influence SOC storage.
As corn (Zea mays L.) hybrids change over time, and with increased use of different plant components for feed, bedding, and energy production, it is important to know macronutrient distribution within plants and how nutrient concentration and accumulation varies during plant development. This field study was conducted in 2007 and 2008 to evaluate dry matter (DM) biomass, macronutrient concentration, and macronutrient content in corn plant fractions (stalk, leaf, tassel, ear shoot, cob, and grain) across developmental stages with two hybrids from 1960 and 2000 eras. Concentrations of N, P, and K were generally lower in all plant fractions for the 2000 compared to 1960 era hybrids, except P concentration in stalks and grain and K concentration in leaves and ear shoots. In contrast, N, P, and K content was consistently higher in 2000 era hybrids for whole plants, leaves, and grain; a reflection of greater DM production. Nitrogen, P, K, and DM content in tassels was lower for 2000 than 1960 era hybrids. From the 1960s to 2000s, hybrid development brought about an increase in plant biomass and grain yield resulting in greater total nutrient content. However, macronutrient concentrations in vegetative plant fractions and grain decreased, thus moderating increase in plant total and grain nutrient content. This research shows the importance for analysis of newer hybrid vegetative and grain biomass on an ongoing basis to provide reliable estimates of macronutrient uptake patterns and removal with harvest of specific vegetative material and grain.
Inoculants containing Bradyrhizobium japonicum are available for soybean [Glycine max (L.) Merr.] production but may not be necessary in fields where soybean previously has been produced. The objective of this study was to determine yield response and probability of an economic return from inoculants in fields with a recent history of soybean production. Fifty‐one inoculant products were evaluated in experiments (n = 73) conducted in Indiana, Iowa, Minnesota, Nebraska, and Wisconsin between 2000 and 2008. Inoculant products were similar and did not produce a yield response relative to an untreated control different from zero (P > 0.05) at 63 environments. Probability for a break‐even economic return at a soybean sale price of $0.33 kg−1 was 59% for Nebraska, 36% for Wisconsin, 25% for Minnesota, 25% for Indiana, and 4% for Iowa. Attaining a return on investment of 67 kg ha−1 (a 2:1 return) reduced success to 11, 2, 1, 7, and 0.2%, for the five states, respectively. Data from this range of environments and products indicate that application of an inoculant offers limited success for either a yield increase or improved economic return on soils where soybean has previously been grown in the upper Midwest.
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