Abstract
The effect of tillage system (NT-no tillage; CT-conventional tillage; MT-minimum tillage; and NT/scarification, every three years) on soybean nutrient availability and yield was evaluated on Oxisol after 12 years of cultivation. Soil samples were collected at depths of 0.00-0.05, 0.05-0.10, and 0.10-0.20 m and were analyzed for P, K, Ca, Mg, carbon (C), organic matter (OM), pH value, potential CEC, base saturation (BS%), and number of semiquinone organic radicals. The macronutrient concentration in the leaves and amount accumulated in the plants at the blooming stage were determined, as well as the yield of the two soybean crops. The soil pH value, BS% and K, Ca, and Mg concentrations were not influenced by the tillage system. The soil P and OM in the surface layer, however, were inversely proportional to the intensity of soil preparation. The P content in the soil surface layer under NT was twice as high as that of soil under CT. The P content in the soybean leaves under NT was also higher compared to that in the plants under CT and MT. The number of semiquinone radicals was low in the soil surface layer under NT, indicating a small degree of humification. However, soybean yield was not affected by the tillage system.
Highlights
It is recognized that a simple change of the cultivation system from conventional to NT does not increase organic matter (OM) throughout the soil profile, some studies have demonstrated that an increase in OM occurs in the surface layer of the soil, mainly from 0 to 0.05 m (Santiago, Quintero, & Delgado, 2008; Aziz, Mahmood, & Islam, 2013; Motschenbacher, Brye, Anders, & Gbur, 2014; Fink, Inda, Bavaresco, Barrón, & Torrent, 2016; Souza, Figueiredo, & Sousa, 2016)
In the early 2000s, Bayer, Martin-Neto, Mielniczukc, and Ernani (2002a) and Pérez et al (2004) used ESR to determine the semiquinone free radical content in humic substances extracted from soils under different management systems as an indicator of changes in OM characteristics
In contrast to the results obtained by other authors, where the pH values of the surface layer were lower in soils under NT systems than in those under conventional tillage (CT) (Grove & Blevins, 1988; Tarkalson, Hergert, & Cassman, 2006; Martínez et al, 2016), pH was not modified by the tillage system in the present study (Tables 2 and 3); this observation agrees with Kibet, Blanco-Canqui, and Jasa (2016)
Summary
It is recognized that a simple change of the cultivation system from conventional to NT does not increase OM throughout the soil profile, some studies have demonstrated that an increase in OM occurs in the surface layer of the soil, mainly from 0 to 0.05 m (Santiago, Quintero, & Delgado, 2008; Aziz, Mahmood, & Islam, 2013; Motschenbacher, Brye, Anders, & Gbur, 2014; Fink, Inda, Bavaresco, Barrón, & Torrent, 2016; Souza, Figueiredo, & Sousa, 2016). There is still a need for long-term studies relating the effect of cropping system to the degree of humification of humic substances (HS) in the surface layer of tropical soils. Martin-Neto, Rosell, and Sposito (1998), using electron paramagnetic spectroscopy (EPR or ESR, from electron spin resonance), detected an increase in the semiquinone free radical content in humic acids extracted from soils with an increase in mean annual rainfall along the temperate grassland climosequence from Argentina. They concluded that OM humification increased with increasing rainfall. In the early 2000s, Bayer, Martin-Neto, Mielniczukc, and Ernani (2002a) and Pérez et al (2004) used ESR to determine the semiquinone free radical content in humic substances extracted from soils under different management systems as an indicator of changes in OM characteristics
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