Recipient Organization
UNIV OF WISCONSIN
21 N PARK ST STE 6401
MADISON,WI 53715-1218
Performing Department
Soil Science
Non Technical Summary
Previous attempts at developing a single soil test that predicts the response of corn to added N have not been successful in Wisconsin (Osterhaus et al., 2008). This project takes the position that response of N cannot be predicted by a single soil measure, but instead, knowledge of the dynamic soil properties are the key to optimizing N fertilizer inputs. Understanding the controls of dynamic soil properties on N cycling, and the related soil management effects on dynamic soil properties are the first steps in developing site-specific N (or at least field specific) N recommendations. Dynamic soil properties are in part related to soil type, but can be altered by long-term soil management. Based on research conducted over the past 15 years, two dynamic soil properties have been shown to be response to soil management: soil aggregate size distribution and particulate organic matter (POM). Soils that have a greater proportion of macroaggregates result in greater physical protection of C and N (Six et al., 2000). The POM represents the active fraction of soil organic matter (SOM), from which the plant available N would originate (Marriot and Wander, 2006). The goals of this research proposal are to utilize long-term research plots to determine how long-term management changes these soil properties and correlate these soil properties to optimum N fertilizer rates. If a link can be shown among dynamic soil properties, response to N fertilizer, and optimal NUE, expanded research in Midwestern cropping systems would be warranted.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
The objectives of this study are to: (1) determine differences in aggregate fractionation, POM, and potentially mineralizable N (PMN) resulting from long-term soil management and (2) determine the net effect of long-term management on response to corn to N. The first hypothesis of this research is that long-term differences in crop management (crop rotation, manure inputs, cover crops) will lead to differences in soil dynamic properties and response of corn to N. The second hypothesis of this research is that long-term crop managements that maximize corn yield with lower rates of N will have greater POM and greater N stored in macroaggregates. Results from this research will be disseminated through peer reviewed publication and through Extension programming such as the Wisconsin Crop Management Conference.
Project Methods
This study will be conducted within the Wisconsin Integrated Cropping Systems Trial (WICST). Five cropping systems treatments will be used in this study. Listed from least diverse/lowest organic input to most diverse/greatest organic input: (1) Continuous corn (annual inputs of inorganic N), (2) Corn-soybean (biennial input of inorganic N), (3) Corn-soybean-wheat (green manure cover crop every third year), (4) Corn-alfalfa-alfalfa-alfalfa (dairy manure applied to corn), and (5) Corn-alfalfa-alfalfa (dairy manure applied to corn). These represent common cash grain and forage-based cropping systems, all aspects of which (N inputs, crop rotation) would affect soil properties and result in different responses of corn to applied N. This study will conduct four measurements at each of the five crop management treatments: (1) aggregate size distribution and N content of each aggregate size class, (2) POM, (3) PMN, and (4) corn yield response to N. Soils will be collected in the fall of each year and aggregate size distribution analysis will be conducted following the method outlined by Gulde et al. (2008). Soils will be fractionated in a two-step process. The first fractionation fractionates soil into macroaggregates, microaggregates, and a silt-clay fraction. The macroaggregates are then further fractionated (through wet sieving) into microaggregates and silt-clay fraction. Each fraction is dried and analyzed for total C and total N. Soils for POM analysis will be collected in the spring prior to planting. The POM will be measured by the method outlined by Marriot and Wander (2006). A simple extraction/filtering technique involving plastic bottles fitted with 53 micrometer mesh screens will be used to measure POM. Soils are dispersed using 5% sodium hexametaphosphate and shaken for one hour. Material retained on the mesh is dried, weighed and analyzed for total C and total N. Soils for PMN analysis will be collected in the spring prior to planting. The 7-day anaerobic incubation method will be used to determine PMN. This method was originally proposed by Waring and Bremner (1964). This simple method is conducted by incubating 5 g of soil in 12.5 mL of water in a test tube. The tube is sealed (and all of the soil is submersed) and placed at 40C for 7 days. After 7 days, 4M KCl is added, the soil is shaken, and the extract is filtered and analyzed for ammonium. The ammonium extraction is also performed on non-incubated samples and the difference in ammonium concentration is the potentially mineralizable N. Within each of the five treatment plots, an area will be established where no external N inputs will be applied. This includes inorganic N fertilizer, manure applications, or cover crop/green manure plantings. Within this area six plots will be established (4.5 x 12m) and will receive 0, 35, 70, 105, 140, or 175 lb/ac of N. Yields will be harvested with a plot combine. Total N uptake will be determined by collecting 10 whole plant samples and analyzing the grain and whole plant biomass for total N. Measures of NUE will be determined as agronomic efficiency (AE), crop recovery efficiency (CREC), and crop removal efficiency (CREM).