Laboratory and in situ methods to evaluate nitrogen mineralization of cattle manure

Abstract

In crop year 2011-2012 (year 1) a field experiment was initiated with the objectives: a) to evaluate net N mineralization rate in area fertilized with manure and planted with maize, using laboratory and in situ methods; b) to correlate N mineralized with N absorbed by maize plants and its production. In the first year of the experiment a support scholarship of a PhD was obtained from FAPESP for the student Fernando Kuhnen (Proc. 2010/10.420-9). In the years 2012-2013 (year 2) the experiment was continued, to evaluate the same plots, and made assessment of N residual mineralization. We intend in 2013-2014 (year 3) and 2014-2015 (year 4) to give continuity to the project. In the year 3 manure will be added using same levels that were done in the year 1 (0, 10, 20, 30 and 40 t ha-1) and in the year 4 the assessment of residual effect will be made. The experiment was installed in a randomized block design with four replications. In the year 3 and 4 the N mineralization rate will be evaluated in laboratory for to determine N-NH4- and N-NO3-, using aerobic incubation with daily variation of controlled temperature (23°C for 10 hours and 28°C for 14 hours), and leaching at 0, 3, 7, 14, 21, 28, 49, 70, 91, 112 days of incubation. In the field, the in situ methods of buried bags and ion exchange resin contained at base of PVC core with undisturbed soil samples will be used. Which method will be installed on all plots on the maize seeding. Buried bags and ion exchange resin will be collected at random, of each plot at 30, 60, 90 and 120 days for analysis of mineral-N. The soil sample of time zero will be collected from each plot to fill the bags, and undisturbed samples will be collected by PVC cylinders on the day of seeding. The results obtained on laboratory and in situ methods will be correlated among themselves and with the N absorbed by maize which will be collected and analyzed at each sampling date of soil and, at last, the yield. (AU)