engleski

The optimizimg of N-fertilization by soil organic matter mineralization

Excess nitrogen (N) fertilization is both an unnecessary cost to producers and a polution risk to graundwater. Appropriate N fertilization requires an accurate estimate of the mineralized from soil organic matter and residue of the previous crop. The objective of this study was to determine the effects of the soil respiration intensity (SRI) as the indicator of soil microbial activity and humus mineralization, respectively. Therefore, the soil samples of five soil types in eastern Croatia were analyzed: the eutric cambisol, pseudogley, rigosol, amphigley and hypogley. The soil samples were taken from soil depths 0- 25 and 25-50 cm. The SRI was determined at several moisture content (SMC ; 60, 70, 80 and 100 % of field water capacity FWC) during 24 h, on three temperature level (9, 21 and 30oC). Also, the humus content (%) was determined, and the amount of released CO2 was converted into the amount of mineralized humus (%) and nitrogen (kg/ha weekly and for whole year). All tested soil samples showed lower humus content in the soil layer 25-50 cm as well as the SRI, compared to upper soil layer (0-25 cm). The increase of SMC resulted mostly by the increase of a difference between samples taken from upper and lower soil layer, measured at all temperature treatments. In general, the lowest SRI was at 9 oC, and the highest at 21 oC, excepting the eutric cambisol where the highest SRI was determined at 30 oC. Based on the SRI, it could be appraised that the mineralization in eutric cambisol was 1.66 kg N/ha weekly at 21 oC and 60 % FWC, while it was 6.89 kg N/ha at 100 % FWC. If such conditions could be maintained whole year, that would be ranged 86.34-359.19 kg N/ha. Under condition of 60 % FWC in whole year, 1.92 % of humus content would be mineralized and 7.99 % at 100 % FWC. On other localities, the estimated amount of mineralized nitrogen in kg N/ha weekly was ranged as follows: 0.74-5.43 (amphigley) , 7.49-9.19 (hipogley), 6.55-9.03 (pseudogley) and 2.89-4.18 (rigosol), respectively. At higher temperatures and optimal humidity it increased to 58.34 kg N/ha weekly on amfigley, 57.40 kg N/ha on hipogley and 54.62 on pseudogley. Concerning that the soil was most of the year cold and wet in natural conditions, or warm and insufficient humid, such high mineralization rates could be expected only in short summer intervals. The results showed doubtless influence of the soil moisture and temperature on the SRI but the relations between moisture and temperature were soil type specific.

soil respiration ; soil organic matter ; mineralization ; soiil water content ; soil temperature ; optimazing N-fertilization

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