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1. Comparison of Mehlich-3, Olsen, and Bray-P1 Procedures for Phosphorus in Calcareous SoilsFertilizer recommendations for P generally are based on soil testing. Although a variety of soil tests are reliable for evaluating plant available P of neutral or slightly acid soils. there is still uncertainty about appropriate soil tests and soil-test interpretations for calcareous soils. The Bray-P 1 and Olsen methods are the most widely used soil-test P methods in the North Central region. Extensive research has shown that the Bray-P1 test is reliable on neutral or acid soils but that it tends... |
2. Foliar Fertilization of SoybeansExtensive research addressed foliar fertilization of soybeans at reproductive stages during the 70s and 80s. The soybean plant has been characterized by markedly reduced root activity during late seed development and increased translocation of nutrients and metabolites fiom other tissue into the seed. This depletion of numents from leaves could result in decreased photosynthesis. leaf senescence. and lower grain yields. Researchers theorized that if nutrients were applied directly to the foliage... |
3. Corn and Soybean Response to Potassium Fertilization and PlacementI\ncreased adoption of conservation tillage, evidence of large within-field nutrient variability, and an apparent increase in the Frequency of crop potassium (K) deficiency symptoms in Iowa and other states have prompted questions about the effectiveness of current soil-test K interpretations and fertilizer recommendations. These questions relate to fertilizer placement and management of within-field nutrient variability. Broadcast placements are less costly than banded placements but they seem inefficient... |
4. Iowa Soil-Test Field Calibration Research Update- Potassium and the Mehlich-3 ICP Phosphorus TestIowa soil-test interpretations and fertilizer recommendations for phosphorus (P) and potassium (K) were last updated in 1999. The only change from previous recommendations (Voss et al., 1996; Voss and Mallarino, 1996) was to add interpretations for the Mehlich-3 (M3) P and K tests to existing interpretations for the Bray-1 P, Olsen P, and ammonium-acetate K tests (Voss et al., 1999). The interpretations for the ammonium-acetate and M3 K tests are similar because comparisons of amounts of K extracted... |
5. Relationship Between Soil P and P in Surface Runoff and Subsurface Drainage- An Overview of Ongoing ResearchNonpoint source pollution fiom agricultural fields has the potential to accelerate eutrophication of fieshwater ecosystems. In a report of water quality in the United States, the Environmental Protection Agency sited agriculture as the primary source of pollution in 60% of impaired river miles, 30% of the impaired lake acres and 15% of estuarine square miles @PA, 1998). Phosphorus, in particular, has received much attention due to its role as limiting nutrient in many fieshwater ecosystems (Correll,... |
6. In-Furrow Starter and Broadcast Phosphorus and Potassium Fertilization for CornIncreasing awareness of potential impacts of farming on the environment has renewed interest in further study of fertilizer management strategies that reduce nutrient inputs. Fertilizer recommendations for phosphorus (P) and potassium (K) usually are based on soil-test values and nutrient removal with crop harvest. Many Midwest fmers follow these recommendations. but many others apply removal-based P and K fertilizer rates even in high-testing soils. The typical farmer applies P and K fertilizer... |
7. Soil-Test Potassium Field Calibrations for Soybean Iowa Interpretations and Research UpdateThere is a long history of potassium (K) fertilization research for soybean and other crops in the North-Central Region. Sustained Iowa field research efforts focused on developing soil-test K (ST10 interpretation and on studying impacts of K fertilization strategies on grain yield and STK. Because of changes in the soil-test K method used in Iowa, this information collected over time should be evaluated separately. The field crop response and STK calibration research conducted Erom the late 1960s... |
8. Swine Manure Phosphorus Use for Crop Production in IowaImproving manure phosphorus (P) management guidelines should result in a more efficient use of thls resource for crop production and in lower risk of P loss to surface water resources. Phosphorus fertilizers are widely used in crop production, there is a great deal of information about their use, and farmers have little doubt about their value to improve crop yield in low- testing soils. However, there is a great deal of uncertainty concerning the value of manure nutrients for crops and about cost-effective... |
9. Assessment of the Combined Effects of Soil pH and Carbonates on Soybean Yield and Development of Iron Deficiency ChlorosisSoybean is extensively grown in areas of the Midwest where fields often have areas of acid to calcareous soils intermingled in complex spatial patterns. Soil pH is highly buffered by carbonates, and measured pH usually ranges from 7.5 to 8.3 depending on the concentration of C02 and other factors. Soybean grown on high-pH calcareous soils often shows iron (Fe) deficiency chlorosis (IDC). Symptoms of IDC include yellowing of interveinal areas of young leaves and, as the deficiency becomes severe,... |
10. Starter Potassium for Corn: Why and WhenStarter fertilizer application can complement broa dcast P and K fertilization for corn and other crops. Questions about its use relate mainly to the conditions in which it is most effective (such as soil-test level, tillage syst em, and broadcast fertilization rates among others), application methods and rates that do not damage seedlings, and nutrient ratios. Many studies in Iowa and the Midwest have shown that starter mixtures (usu ally N-P or N-P-K) often increase early corn growth. Corn yield... |
11. Foliar Fertilization and Fungicide Application for SoybeanConcerns over fungal diseases in soybean have renewed interest in applying pesticides for disease control with the goal of increasing grain yi eld. Interest has especially been sparked by discussions of the possibility of Asian Soybean Rust (Phakopsora pachyrhizi) spreading north to the North Central region. Because of increasing prices of soybean grain and traditional fertilizers, many Midwest grower s are considering mixing fluid fertilizers and fungicides for foliar application to soybean. Extensive... |
12. Testing Field-Moist Soil For Potassium And Other Nutrients - What's It All About?Potassium (K) is present in the soil in water-soluble, exchangeable (both readily available for crops), non-exchangeable or fixed (may become available over time), and mineral (unavailable) forms. Estimates of soil exchangeable K with the ammonium-acetate and Mehlich-3 extractants from air-dried or oven-dried soil samples are the most widely used soil-test methods for K. These methods provide comparable K test results, and are suggested for the north-central region by the North-Central Regional Committee... |
13. Plant Availability of Phosphorus From Struvite Produced During Corn Bioenergy ProcessingThere is strong interest on recovering nutrients from the waste stream of industrial processing of crop biomass for bioenergy so they can be efficiently utilized as fertilizer materials. Phosphorus (P) can recovered as struvite [NH 4Mg(PO4).6H2O] from the aqueous stream. A low P water- solubility in struvite and previous research with the pure mineral or struvite precipitated from liquid animal manure suggest a slow-release of P from struvite. However, a recent short-term greenhouse study in Iowa... |
14. Potassium Management, Soil Testing and Crop ResponseNew field research is conducted in Iowa as issues or questions arise to assure that nutrient management guidelines are up to date and to address new issues. This article briefly summarizes two major projects with potassium (K) whose results are useful to improve the efficacy of nutrient management and crop production. One project focused on correlating soil-test K methods with response of corn and soybean to fertilization and on obtaining better estimates of the concentration of K in corn and soybean... |
15. Long Term Phosphorus Studies and How they Effect RecommendationPhiosophiesProfitable crop production requires adequate levels of phosphorus (P) and other nutrients. Careful planning is required because of volatile grain and fertilizer prices and increasing public concerns about water quality impa irment due to excess nutrient loss from fields. Higher fertilizer prices may not be a major issue as long as the hist orical ratio between crop and fertilizer prices is approximately maintained, becomes more favora ble, or increases can be predicted. Largely unpredictable price... |
16. Evaluation of Plant-Available Phosphorus of Dried Residuals from Wastewater Processed for Phosphorus Reduction with Aluminum or IronABSTRACT Wastewater effluent from industrial and municipal water treatment plants requires phosphorus (P) removal before being discharged to surface waters. The resulting residual materials, with elevated P concentration, are usually land applied. Basing P application rates on the nutrient value for crops is the most rational way to utilize this P resource because it would improve farmers economic return while... |
17. High Gypsum Application Rates Impacts on Iowa Soil Properties, Dissolved Phosphorus Loss, and Crop YieldGypsum (calcium sulfate) is a common sulfur (S) source for crops and rates in the northcentral region seldom are > 250 lb/acre. It is known that even higher gypsum rates do not raise soil pH. Research in eastern or southeast states showed that in some conditions high gypsum rates can improve other chemical or physical properties and can reduce dissolved phosphorus (P) loss from fields. However, little research has evaluated potential benefits in prairie-developed soils of Iowa and the region.... A.P. Mallarino, M.U. Haq |