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| Author(s): |
Silvino Guimarães Moreira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2003-03-07 |
| Advisor: | Luis Ignacio Prochnow |
| Abstract | |
With the objective of evaluating the bioavailability of micronutrients in soils cultivated with soybean under no tillage (NT), two studies (1 and 2) were conducted at field conditions. Study 1 was carried out under an OxisoI Iocated in Ponta Grossa, PR, which was submitted 12 years to four different tillage treatments (NT, conventionaI tillage - CT, minimum tillage - MT and NT/scarification each 3 years). Study 2 was carried out in nine sites of Tibagi, Ponta Grossa and Castro, PR, with and without previous Mn deficiency in soybean. In four sites was applied Mn rates, varying of 0 to 48 kg ha-1 In both studies, the availability of soil micronutrients was studied by extractants Mehlich I and III, HCI 0.1 moI L-1 , DTPA-TEA pH 7.3 and by the sequential extraction (exchangeable, organic, oxides and residual). The soil samples were collected from the layers of 0.00-0.05, 0.05-0.10 and 0.10-0.20 m (study 1) and 0.00-0.10 m (study 2). In the soil samples from the 0.00-0.05 and 0.05-0.1 O m (study 1) and 0.00- 0.10 m (study 2) was extracted humic acid (HA) in order to study the interaction of metaIs and HA, using the electronic paramagnetic resonance (EPR). Leave samples (study 1) and representative top plants (study I and 2) were collected and contents of macro and micronutrients analytically determined. In the study I, extractable soil Mn determined by all extractants in the soil layer of 0.00-0.05, and in the average of all extractants in the soil layers of 0.05-0.10 and 0.00-0.20 m, were higher in the NT as compared to the CT. The same effect was obtained for Zn in the layer of 0.00-0.05 m in the average of all extractants. The percentage of Mn in the organic form in the 0.00-0.05 m soil Iayer was higher in the NT and NT with scarification as compared to the CT. The hígh amounts of Fe oxides in the HA samples did not make possible to obtain signals for Cu and Mn, even afier long high speed centrifugation of samples. Soybean yield was not affected by tillage systems. In the case of study 2, manganese rates applied affected directly the extractable soil Mn, but not the leave concentration or the uptake of Mn by the plants. Exchangeable, organic and oxide forms of Mn increased with rates applied in soils with previous Mn deficiency for soybean, with the highest increase for the organic fraction (5.4 to 35.1 mg kg-1 of Mn from the control to the highest rate of Mn applied, i.e., 48 kg ha-1). Manganese was not detected by EPR in the solid samples of AH - pH 3.0. Manganese quantification in the same samples, after nitric percloric digestion, plus clear signs for Mn by EPR in samples of AH - pH 2.4, Iead to the idea that Mn was strongly linked to the functional groups of AH. Soybean yield was not affected by manganese rates. The DTPA-TEA was the most reliable extractor for the element in order to evaluate Mn bioavailability to soybean under NT. (AU) | |