Soil chemical properties under a no-tillage system : Forage grass seeding modes of gender urochloa intercropped with maize

Different farming practices and soil management can make changes in the chemical properties of the soil. In this sense, the monitoring of these possible changes is essential for proper soil correction and/or using systems that are more sustainable. The objective of this work was to verify the behavior of the chemical attributes of a Latosol (Oxisol) under a no-tillage system of plantation, by intercropping maize with two species of forage grasses in different methods of sowing. The experiment was conducted in an area of the Laboratory of Agricultural Equipment and Mechanization of Universidade Estadual Paulista “Júlio de Mesquita Filho” (UNESP, São Paulo State University), in Jaboticabal, Brazil, and the treatments were maize intercropped with two species of grass, of the Urochloa gender, namely Urochloa brizantha cv and Urochloa ruziziensis cv, sown in four modes: maize with Urochloa in row seeding (MFL); maize with Urochloa between rows, sown on the same day of the sowing of maize (MFE); maize with Urochloa sown in rows, covered by fertilizer at the V4 stage (MFC); maize with Urochloa, sown by casting, along with fertilizer cover at the V4 stage of maize (MFLA) and maize alone, without any intercropping (control). Composite samples were taken for chemical analysis (P, MO, Ca, Mg, K, H + Al, SB, T, and V) in layers from depths 0.00 to 0.10 m; 0.10 to 0.20 m; and 0.20 to 0.30 m. The experimental design was that of randomized blocks, with nine treatments, in a factorial design (2×4) +1, with four replications. Major changes were observed in the soil chemical attributes in layer 0.10-0.20 m, within modes MFE and MFLA. In the no-till system, Urochloa brizantha cv has greater cycling of Ca 2+

formation of straw and the production of grain, a fact observed almost wherever in the state of São Paulo as well as in the Brazilian Midwest (Barducci et al., 2009).In tropical regions, the decomposition of organic material is faster and this fact is worthy of greater attention by producers (Liu et al., 2010).In recent decades, with the advancement in research and the use of new technologies, a change is happening in the agricultural sector, which is explained by the incorporation of more intensive processes in production systems (Barcellos et al., 2008).Among planting systems used by producers, the no-till is considered the most conservationist, for recommending the supply of coverage over the soil, rotation and intercropping.In the no-till system, intercropping is an alternative aimed at increasing the sustainability of the agricultural production model, because the consortium of crops changes the physical, chemical and biological soil properties over time, may favor the improvement of the sustainability of agricultural systems as a result of yield diversity (Garcia et al., 2008;Calonego et al., 2011).
The maize crop has excelled in integration with forage grass for providing increased straw provision for the maintenance of tillage, in addition to allowing the use of the dry mass after harvest, used in animal feed during periods of lower supply of pasture.Barducci et al. (2009), claim that the implanted forage grass species in the consortium is crucial for obtaining good yields of both maize grains and accumulation of forage grass dry matter.Various forage grass species stand out in intercropping with maize, but in the literature are found a few that stand out, such as B. brizantha cv, B. ruziziensis cv, Panicum maximum cv.Tanzania and P. maximum cv.Mombaça, (Pereira et al. 2014).Forage grasses provide large amount of mass (dry matter), according to Costa et al. (2014) the Urochloa brizantha cv. and Urochloa ruziziensis cv are good alternatives in the production of straw under no-tillage.Thus, forage grasses protect the soil for longer against erosion and change the physical and chemical properties of soil through nutrient cycling and aggregate stability (Loss et al, 2011;Seidel et al, 2014).It is extremely valuable to understand the dynamics of soil properties, be they of physical, biological or chemical order, in view of the direct influence of these factors in the success of agricultural production.Thus, the monitoring of soil fertility levels is important not only for the correct nutritional supply of crops, but also to allow that adequate management practices of fertilization and soil preparation are performed efficiently, enabling improvements in management practices in order to improve the production and crop management (Tasso Júnior et al., 2010).
The no-tillage improves soil chemical conditions due to the level of organic matter from straw, contributing to soil cover, while maintaining system stability (Chioderoli et al., 2012a).Also, according to Mateus et al. (2012), the simple fact of maintaining straw in the soil, increases the level of organic matter, phosphorus, potassium, calcium, dos Santos et al. 5051 magnesium, pH, effective CEC and micro-nutrients on the soil surface, as well as there is a decrease of exchangeable Al.Freitas et al. (2014) reported that the main chemical changes in cultivated soils compared to the original conditions, are due to the variation of pH and cation levels.The chemical properties of the soil are affected by the removal of natural vegetation and cultivation, mainly on its surface, due to the addition of lime and fertilizers and agricultural operations.According Zanão Junior et al. (2010), in the no-tillage system (SPD), the management itself, such as the surface application of limestone, fertilization, accumulation of crop residues, can alter the soil chemical fertility.Thus, the adoption of certain management practices, such as surface fertilizer; sowing by casting; sowing in rows; crop residues in succession and/or rotation over the years, contribute in the dynamic behavior of the soil chemical properties.In this sense, the evaluation of soil chemical properties is required due to the heterogeneity of these attributes, especially when associated with methods of sowing and intercropping.Therefore, the objective of this study was to evaluate the behavior of soil chemical properties due to the consortium maize-forage grass of the Urochloa species under different methods of sowing.

MATERIALS AND METHODS
The experiment was conducted in the experimental area of the  (Embrapa, 2006), or "Ferralsol", according to the FAO Soil Classification, aka "Oxisol"), with a particle distribution of 200 g/kg sand, 290 g/kg silt and 510 g/kg clay.The experimental area was being treated in the SPD for over ten years.The climate, according to Koeppen classification is Aw, defined as tropical humid, with a rainy season in summer and a dry winter, with an average annual rainfall of 1,425 mm and an average temperature of 22°C.The precipitation, maximum temperature, minimum and average ( °C) during the experiment are shown in Figure 1.
The treatments consisted of two species of Urochloa (U. brizantha cv and U. ruzizienses cv) and four modes of intercropping of urochloas with maize, namely: maize with Urochloa at sowing line (MFL); maize with Urochloa between rows, sown on the same day of the sowing of maize (MFE); maize with Urochloa sown between rows, covered by fertilizer at the V4 stage of maize (MFC); maize with Urochloa sown by casting, with surface fertilization at the V4 stage of maize (MFLA), and maize without intercropping (control).Maize received basic fertilization in two growing years, of 300 kg/ha of the commercial formula (08-28-16) with supplementary cover fertilization at the V4 stage, corresponding to 120 kg/ha of potassium chloride and 300 kg/ha urea, while for soy, the basic fertilizer was 250 kg/ha commercial formula (04-20-20), and for Urochloas, we used 20 kg/ha commercial formula (08-28 -16) for forage grass seeding between rows (MFE) and at the time of the maize crop at the V4 stage (MFC), being the fertilizer used only as a vehicle for distribution of seeds.The experimental design was a randomized block design, with nine treatments in a factorial scheme (2×4) +1.Two forages of the genus Urochloa (Urochloa brizantha Each experimental plot consisted of eight maize lines (DKB 390) for a population of 60 thousand ha -1 plants, with 0.90 m row spacing, sowing density of 5.4 m -1 seeds and 14 Soybean cultivar Valiosa Roundup Ready, spaced at 0.45 m.The plots were 25 m long, 15 m haulers for machine and equipment maneuvers, useful area corresponding to the two maize lines and three soybean rows with five meters each, discounting the ten meter border in each end.Soil samples were collected from depths of 0.0-0.10;0.10-0.20;0.20-0.30m for subsequent chemical analysis (P, MO, Ca, Mg, K, H + Al, SB, T, and V), following the method proposed by Raij et al. (2001).Data were submitted to analysis of variance by the F test (p<0.05)and when significant, factorially compared to the control group (maize, only) and this comparison performed by applying Dunnett's test (p<0.05).Statistical analyzes were performed by using a statistical software, Assistat, version 7.7 (beta) Silva and Azevedo (2016).

RESULTS AND DISCUSSION
In general, the soil chemical attributes in the layer from 0.0 to 0.10 m do not differ statistically among themselves by Dunnett test (p<0.05)presented in Table 1.The nonsignificant difference among the soil chemical properties in the layer from 0.0 to 0.10 m, may possibly be explained by the short development period of the study, which lasted one agricultural years.However, the phosphorus levels were higher and significantly different within modes, MFLA (Casting V4) and MFL (Rows), and possibly these results may be due to the process of decomposition of the roots of Brachiaria, releasing nutrients, together with the colloids present in latosols, as kaolinite clays, Fe and Al oxides, favoring greater fixation of phosphorus.
Another factor that may be contributing to the higher phosphorus values within modes (sown by casting in V4 stage) and (in the maize planting row), is the pH, since as it rose there was an increase in the phosphorus level, and this may be due to competition between the OH anions (from the rising pH) and H 2 PO 4 -and HPO 4 2-from the surface of colloids.With regard to the detailing for the phosphorus level, forage grasses within the modes, as well as modes within forage grasses (Figure 2) , it is noticed that there was an increase in the phosphorus level within modes MFL (Rows) and MFLA (Casting V4) for forage grasses U. ruzizienses cv and U. brizantha cv respectively.Means followed by same letter do not differ at Tukey test 5% probability.Forages: U .B -(Urochloa brizantha); U.R -(Urochloa ruziziensis); sowing modalities: MFL -(Maize with urochloa in the sowing line), MFE -(Maize with urochloa in the interweave, sown on the same day as maize sowing), MFC -(Maize with urochloa in the seeded line together with the cover fertilizer in the V4 stage), MFLA -(Maize with urochloa on the haul along with maize V4 maize mulch).These results may be due to continuous fertilization in rows and between rows (Ciotta et al., 2002;Costa et al., 2009), in addition to biopores formed by the roots and soil fauna (Adiscott, 1995), promoting redistribution of P in the profile and by its low mobility in the soil.Furthermore, the soils in the tropical regions have clays with high fixation  ----------------------mmolc dm  -3 ----------------------(  capacity of phosphorus (Ferreira et al., 2014).For the values of chemical parameters of the soil in depth from 0.10 to 0.20 cm (Table 2), in general, significant differences in the interaction between grasses and modes for the pH, Mg, H + Al, SB and V, as detailed in Figures 3, 4, 5, 6 and 7 respectively.Nascente et al. (2014), by studying the chemical attributes of an Oxisol under no-tillage affected by soil management and crop rotation, concluded that chemical attributes Ca, Mg, organic matter, P, K, concentrated in the most superficial layer, regardless of rotation used in managements with lesser soil revolving.With the exception of phosphorus, which is found in the between rows mode for Urochloa ruziziens, the other attributes (pH, Mg, SB, T and V) had higher values observed in mode Casting V4 for Urochloa brizantha cv, (Table 2).-------------------------mmolc dm  -3 ---------------------(%   These results can be explained by the low competition occurring between maize and forage grasses in the vegetative stage V4 of maize, together with supplementary surface fertilization and a higher pH value, where higher pH values contributed directly in the reduction of potential acidity levels (H + Al) and increased levels of Mg, SB and V (Strojaki et al., 2013).Also with respect to the pH, when it is increased, there is also an increased mineralization of organic matter, and this process is favored in soils of pH values between 5.0 and 6.0, freeing N, P and S, as well as macro and micronutrients in smaller amounts (Cardoso et al., 2014).For the detailing of pH (Figure 3), the Urochloa ruziziensis cv showed higher pH levels in the MFE mode differing from the others.For Portugal et al. (2010), the forage grass Urochloa ruzizienses cv has a positive effect on the increase of cations in the soil, which can positively affect crop productivity in the short and long run  As for the magnesium levels (figure 4), the highest values were found in the MFE mode for Urochloa ruzizienses cv, differing from the others.This result can be explained by the nutrient cycling capacity that have the Urochloa ruzizienses cv, together with the fertilization carried out between rows.Dalchiavon et al. (2012), by evaluating the spatial variability of fertility of an oxisol under no-tillage system, report that high Mg 2+ levels, layered from 0.10 to 0.20 m, occured by providing considerable amounts of exchangeable bases during liming.
Means followed by same letter do not differ at Tukey test 5% probability.with urochloa in the interweave, sown on the same day as maize sowing), MFC -(Maize with urochloa in the seeded line together with the cover fertilizer in the V4 stage), MFLA -(Maize with urochloa on the haul along with maize V4 maize mulch).To have the contents of H + Al (figure 5), higher values within the MFE mode were found, as a greater value for Urochloa brizantha cv.This result is explained by the pH increase in the same mode (figure 3).According to Steiner et al. (2011), the potential acidity has a behavior opposite to that of the pH, therefore, as the pH is raised, the potential acidity tends to decrease.The author comments that when the pH is increased in depth it is due to the downward movement of Ca  3. Average values of the soil chemical parameters, evaluated in the layer from 0.20 to 0.30 m, according to the sowing mode and forage grass species.

Figure 2 .
Figure 2. Ramifications of interaction between factors, sowing modalides and fodder for the variable phosphorus.

Figure 3 .
Figure 3. Ramifications of interaction between factors, sowing modalides and fodder for the variable pH.

Figure 4 .
Figure 4. Ramifications of interaction between factors, sowing modalides and fodder for the variable magnesium.

Figure 5 .
Figure 5 .Ramifications of interaction between factors, sowing modalides and fodder for the variable H + Al.

Figure 6 .
Figure 6.Ramifications of interaction between factors, sowing modalides and fodder for the variable SB.

Figure 7 .
Figure 7. Ramifications of interaction between factors, sowing modalides and fodder for the variable V.
2+ and Mg 2+ to deeper soil layers.However,Oliveira et al. (2002) observed that in the no-tillage system the higher pH values are found in the surface layer up to 0.10 m.Means followed by same letter do not differ at Tukey test 5% probability.Forages: U.B -(Urochloa brizantha); U.R -(Urochloa ruziziensis); sowing modalities: MFL -(Maize with urochloa in the sowing line), MFE -(Maize with urochloa in the interweave, sown on the same day as maize sowing), MFC -(Maize with urochloa in the seeded line together with the cover fertilizer in the V4 stage), MFLA -(Maize with urochloa on the haul along with maize V4 maize mulch).For SB levels (figure6) the highest values were found in the MFLA mode for Urochloa brizantha cv, both for forage grasses within the modes and to the modes within the forage grasses.This result can be explained by higher values of Ca 2+

Table 1 .
Average values of the chemical soil parameters, evaluated in the layer from 0.0 to 0.10 m, according to seeding mode and forage grass species.

Table 2 .
Average values of the chemical soil parameters evaluated in the layer from 0.10 to 0.20 m, according to seeding mode and forage grass species.