Steve Prochaska, Extension Agriculture and Natural Resources Agent
To measure soil-test levels over time and cropping in a field gridded in geospatially referenced 0.33-acre plots.
| Cooperator: | Ohio State University Extension | Herbicide: | |
| Unger Farm | POST | Basis Gold 14 oz/A + Banvel | |
| County: | Crawford | 4 oz/A + Crop oil 1 pt/A | |
| Nearest Town: | Bucyrus | (5/5/01), 160 lb/A actual N | |
| Soil Type: | Pewamo clay loam and | sidedressed as 28% (6/18/01) | |
| Blount silt loam | Variety: | Various site of OSU Corn | |
| Drainage: | Systematic | Performance Trials and OSU | |
| Previous Crop: | Corn | Bt trial | |
| Tillage: | Chisel plow and field cultivator | Planting Rate: | Various depending on hybrid |
| Soil Test: | pH 6.6, P 126ppm, K 490ppm | Row Width: | 30 inch |
| Fertilizer: | 0-44-60 lbs N-P2O5-K2O per A | Planting Date: | May 5, 2001 |
| (4/19/01), starter 30-0-0 lb/A | Harvest Date: | October 26, 2001 |
Soil sampling is essential to maximizing economic returns and protecting the environment in grain crop production systems. To the above ends, grid soil sampling (GSS) has recently been implemented by a number of Ohio farmers with the purpose of gathering soil-test information on small areas of a field. By GSS, field points are geo-referenced, thus permitting application of varying amounts of fertilizer or lime. Further, overlaying soil test results, yield maps, soil type maps, topographic maps, etc., can develop spatially referenced information for specified small areas of a field. Thus, better associations of the factors influencing yield can be calculated. Traditional crop soil tests (most 10 acres in size or larger) and their associated results are often quite variable, which can cause a crop to be over or under fertilized.
Thus, an analysis on six 0.33-acre grids selected randomly from a total of 15 grids was conducted to examine the stability of soil test P, K, and pH over time and cropping systems. The soil tests were taken in November of each year. The soil samples were taken at the same position in the field (using GPS) over time. There were no crops grown in 1997, when initial soil samples were taken. This study attempts to eliminate spatial bias by the repeated use of very small grids to describe soil nutrient variability.
| Table 1. Soil pH of Six Selected Grids Over 5 Years. | |||||||
| Year | Grid 1 | Grid 2 | Grid 3 | Grid 4 | Grid 5 | Grid 6 | Average |
| 2001 | 6.2 | 6.7 | 6.4 | 6.5 | 7.4 | 7.4 | 6.63 |
| 2000 | 6.7 | 7.0 | 6.6 | 6.6 | 7.4 | 7.4 | 6.83 |
| 1999 | 6.6 | 7.0 | 6.5 | 6.4 | 7.3 | 7.3 | 6.70 |
| 1998 | 6.4 | 7.2 | 6.4 | 6.8 | 7.3 | 7.3 | 6.78 |
| 1997 | 7.3 | 7.1 | 7.2 | 6.7 | 6.8 | 6.8 | 6.98 |
| LSD (0.05) | NS | ||||||
| F | <1 | ||||||
| CV (%) | 5.2 | ||||||
| Table 2. Soil P2O5 (ppm) of Six Selected Grids Over 5 Years. | |||||||
| Year | Grid 1 | Grid 2 | Grid 3 | Grid 4 | Grid 5 | Grid 6 | Average |
| 2001 | 34 | 24 | 21 | 33 | 34 | 23 | 28 |
| 2000 | 48 | 38 | 40 | 31 | 57 | 32 | 41 |
| 1999 | 40 | 36 | 39 | 37 | 36 | 44 | 39 |
| 1998 | 39 | 33 | 33 | 24 | 26 | 24 | 30 |
| 1997 | 10 | 16 | 26 | 19 | 15 | 13 | 17 |
| LSD (0.05) | 7.8 | ||||||
| F | 13.3 | ||||||
| CV (%) | 21.2 | ||||||
| Table 3. Soil K2O (ppm) of Six Selected Grids Over 5 Years. | |||||||
| Year | Grid 1 | Grid 2 | Grid 3 | Grid 4 | Grid 5 | Grid 6 | Average |
| 2001 | 145 | 126 | 116 | 170 | 123 | 142 | 137 |
| 2000 | 161 | 126 | 180 | 143 | 137 | 130 | 146 |
| 1999 | 131 | 120 | 142 | 165 | 104 | 133 | 133 |
| 1998 | 180 | 135 | 172 | 149 | 88 | 136 | 143 |
| 1997 | 90 | 142 | 155 | 167 | 64 | 158 | 129 |
| LSD (0.05) | NS | ||||||
| F | <1 | ||||||
| CV (%) | 20.8 | ||||||
Phosphate and potassium grain removal rates for 180 bu/A corn (two crop years, 1998 and 2001), 48 bu/A soybean (1999), and 93 bu/A wheat (2000), would be 238 lbs/A P2O5 and 204 lbs/A K2O respectively. The base rate(s) of fertilizer applied in the last four years were 309 lbs P2O5 and 422 K2O. Thus, both P and K soil test levels would be expected to go up. P2O5, however, went down in five of the six grids compared to 2000. K2O soil test levels went down in three of the six grids compared to 2000. The reduction in P, although small, is not explained by the fertilizer applied and crop removal budgets. Other factors, such as time of year of the soil testing and/or soil laboratory calibrations, may have had some impact on the final result. Soil pH was quite stable for five of the six selected grids from year to year.
For more information, contact:
Steve Prochaska
Ohio State University Extension, Crawford County
117 E. Mansfield St.
Bucyrus, Ohio 44820
prochaska.1@osu.edu