Possible methods to incorporate measurements of soil physical properties in Missouri N fertilizer recommendations will be evaluated based on results from the field trial and other available research in the state. These methods may include a modifier that reduces yield goals in soils with physical restrictions or an index that increases or decreases N fertilizer recommendations based on observed changes in N fertilizer efficiency with increasing physical restrictions.
Current Status and Importance of Research:
Natural and induced soil physical restrictions to crop growth are a common problem in Missouri soils. These restrictions include claypans, tillage pans, fragipans and compacted soil layers. Soil physical properties affect several soil processes including the rate of water infiltration into soil, soil moisture availability to plants, and nutrient transformations. Due to the importance of soil physical properties for root growth in Missouri soils, Scrivner et al. (1985) developed a soil productivity index for Missouri that included measurements of potential available water capacity (a property related to soil texture), bulk density and soil pH by depth to predict root growth.
Reduction in agricultural production due to physical restrictions, such as soil compaction, has been attributed to poor soil aeration, the high penetration resistance of compacted soils to root growth, and increased nutrient losses (Hillel, 1980). Soil physical properties that increase soil moisture may also reduce rates of N mineralization due to increased anaerobic conditions. Additional negative effects of processes affected by soil physical properties, such as soil compaction, are increased potential for environmental contamination due to reduced water infiltration and increased surface runoff, soil erosion, and transport of agricultural chemicals and nutrients in runoff to aquatic systems (Håkansson and Voorhees, 1997).
Although crop yield potential may be reduced in soils with physical restrictions, current N fertility recommendations from the University of Missouri for agronomic crops do not account for the effects of soil physical properties on crop production. In fact, research has shown that non-sandy Missouri soils with bulk densities greater than 1.3 g cm-3 have reduced potential productivity for crop growth (Scrivner et al., 1985). Among the current factors affecting N fertilizer recommendations are type of crop, yield goal, and soil organic matter content. A better understanding of the relationships between soil physical properties, fertilizer N efficiency and yield of field corn will assist in developing improved fertilizer management practices for soils with physical restrictions, such as higher or lower N fertilizer rates, and changes in fertilizer placement and timing of application. In addition, quantification of yield reductions due to soil physical restrictions will aid producers in management decisions.
Timetable:
| April, 2001 | Apply and establish N fertilizer and compaction treatments |
Plant experiments
| April-Sept., 2001 | Sample and analyze soil and plant tissue
Test soil physical assessment methods |
| Sept./Oct, 2001 | Harvest experiments and sample and analyze soil and plant tissue |
| November, 2001 | Analyze research results |
| December, 2001 | Annual report |
| April-Nov. 2002 | Same as 2000 |
| December 2002 | Submit final report |
Expected Benefits and Strategy for Application/Transfer of Knowledge:
The addition of an assessment of soil physical restrictions in calculating N fertilizer recommendations will improve N fertilizer management and provide growers with important information to manage a major soil physical factor that limits crop yield. This proposed project will also increase our knowledge of the fate of N fertilizer applied to claypan soils with physical restrictions. Additional information will be developed for the potential use of rapid and inexpensive methods to assess soil physical properties. It is anticipated that including soil physical properties as a factor in N fertilizer recommendations for Missouri will require additional calibration and testing for the major soil types around the state.
The results of this project will be incorporated into research and extension publications and workshops. A graduate student will receive support under this grant for their graduate dissertation research training.
References
Håkansson, I. and W.B. Voorhees, 1997. Soil compaction. p. 167-179. In R. Lal, W.H. Blum, C. Valentine and B.A. Stewart (eds.) Methods for assessment of soil degradation. CRC Press, Boca Raton, FL.
Hillel, D. 1980. Fundamentals of soil physics. Academic Press, San Diego, CA.
Scrivner, C.L., B.L. Conkling, and P.G. Koenig. 1985. Soil productivity indices and soil properties for farm-field sites in Missouri. Agricultural Experiment Station, University of Missouri-Columbia, Columbia, MO.
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