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Soil FertilityWICST has monitored the status of available potassium and phosphorus under the various cropping system since the start of the Trial. Because leaching and other losses are generally minimal with these two nutrients, changes in soil test levels should be directly related to inputs (fertilizer and manure) and output (crop removal). The average initial soil test phosphorus (STP) and soil test potassium (STK) levels at the start of the trial were very high at both WICST sites. Generally speaking it is considered that there is no response to fertilizer if STP is above 30 ppm and STK above 140 ppm for these rotations on the medium textured soils of southern Wisconsin. As a result, except for the advantages of starter fertilizer placement next to the seed in cool soils on the high input systems, no fertilizer was added during the first years of the trial. As mentioned earlier, manure additions on the forage systems (CS4 and CS5) were based on the estimate that at current stocking rates, dairy herds annually produced an average of 10 ton of manure per tillable acre. STP and STK in almost all the treatments dropped by the fall of 1999 but remained excessively high for soil phosphorus and was approaching “high” levels for potassium after a full nine seasons of intensive cropping. The major exceptions were CS4 and CS5 at Lakeland where forage yields were modest and the drier pack-manure used on the plots were higher in total phosphorus and potassium per ton than at Arlington. The grazing plots at Lakeland also saw an actual increase in STP and STK since they were heavily manured in 1996 prior to reseeding the paddocks. |
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