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The effect of integrated management practices on crop and soil nutrient dynamics

Slawinski, K.R. 2010. University of Manitoba


This study was undertaken to evaluate the pattern of release and uptake of N for durum wheat (Triticum durunt Desf. cv. AC Avonlea) grown on field pea(Pisum sativaL.) stubble in 2002 and 2003 under a range of management systems including (i) organic (no inputs), (ii) organic with composted beef cattle (Bos taurus) manure, (iii) synthetic fertllizer, no pesticides, (iv) Pesticide Free Production (PFPTM) (synthetic fertilizer, pesticides used before crop growth and in other crops in the rotation, no pesticides applied to the growing target crop and no residual pesticides) and (v) integrated management (synthetic fertilizer, pesticides applied as required). Regardless of management system, the greatest soil NO3- contents were generally observed between the time of seeding and the first crop stage sampled with maximum crop N accumulation occurring by anthesis. Measured soil and crop N variables tended to be greatest in systems receiving synthetic fertilizer. The strictly legume and legume and composted manure based fertility systems were not able to supply sufficient N for optimum crop production based on a sufficiency N concentration of 2 to 3%o in the whole plant prior to filling. Systems receiving synthetic urea fertilizer without pesticides also experienced N limitations in response to competition from significantly higher weed biomass. The PFP™ system was able to produce dry matter and final grain yields comparable to the integrated management system suggesting effective crop production may be possible in a reduced pesticide system as long as adequate nutrients are available to meet crop demand. The effectiveness of Plant Root SimulatorrM (PRS) probes and the Illinois soil N test (ISNT) for predicting soil N release through the growing season were also evaluated. Good relationships were found between mid season PRS-NO3- and crop N uptake (r: 0.5 1 * and 0.64* *) in 2002 and 2003 respectively. Although a greater correlation was observed between mid season soil NO3- content and crop N uptake compared to mid season PRS-NO3- and crop uptake, no significant correlation was observed between early season NO3- concentrations and crop N uptake. There was no correlation between ISNT- N and crop N uptake in either year of study. The ISNT was not a reliable indicator of potential N release under Manitoba conditions, based on the critical value of 300 mg kg-l suggested for soil samples collected from a 0-15 cm depth from corn sites in lllinois. The lack of strong, consistent relationships between early season assessment of N release potential and crop N uptake make it difficult to use these indices for adjusting recommended fertilizer rates.