Pasture recovery with the application of agricultural gypsum associated with nitrogen fertilization

The presence of toxic aluminum in the soil and N deficiency are one of the main causes of degradation of cultivated pastures, mainly of the Urochloa genus. The use of agricultural gypsum for restoring soil fertility is one of the ways to recover the productive capacity of degraded areas. Given the above, the work aims to assess pasture recovery with the application of agricultural gypsum associated with nitrogen fertilization. The experimental design was randomized blocks in a 3x4 factorial arrangement, that is, absence of nitrogen, 50 kg ha in the form of ammonium nitrate and 50 kg ha urea, interacting with four doses of agricultural gypsum, namely: 0 ; 750; 1500 and 3000 kg ha and with four replications, totaling 48 plots. The use of urea as a source of N resulted in a higher plant height (PH) when compared to the use of ammonium nitrate, representing a relative increase of approximately 12% in relation to the control. Dose of 1730.8 kg ha of agricultural gypsum resulted in a maximum production of 4.97 t ha of dry pasture. The linear interaction of the use of ammonium nitrate with gypsum doses shows an extremely interesting synergistic potential with this source. For dry mass of culms (CDM), the use of urea had a PMTE of 1730.8 kg ha of agricultural gypsum resulting in 2.38 t ha. The culms dry mass of (CDM) represented 47.9% of the total dry mass of the pasture.


Introduction
In the Brazilian agricultural scenario, the ruminant production systems absorb a lot of technology and innovation in order to raise the zootechnical indexes related to animal quality and productivity. In systems qualified as extensive, these being predominant in the national territory (Dias et al, 2015), great part of the initial investment is destined to the implantation of pastures with forages that present nutritional quality aiming to supply the needs of the herds (Dim et al, 2015), since this represents the largest portion of the animal food tract due to the practicality of cultivation (Porto et al, 2017).
In the Brazilian cerrado, approximately 53 million hectares are considered as pasture for livestock. However, part of the pastures cultivated in Central Brazil is in some state of degradation, it is estimated that 80% of these are evolutionary process of loss of vigor. The description of soil degradation is linked to soil quality, that is, from negative changes in characteristics, a process of degradation is associated. The loss of chemical nutrients in the soil, responds to the fall of its fertility, due to the reduction of macro and micronutrient contents and by the contents and quality of organic matter. The loss of chemical nutrients in the soil, responds to the fall of its fertility, due to the reduction of macro and micronutrient contents and by the contents and quality of organic matter (Bilibio, 2010).
Usually, there is an increase in the levels of Mn and Al, due to the reduction in pH. To obtain good indicators of soil quality, a combination of physical, chemical and biological attributes will occur, which together, hypothetically, would represent an ideal combination in order to provide optimal conditions for plant development and maximum expression of their biological potential (Colodel et al, 2018). In this sense, alternatives should be sought in management that are simple, economically viable and that contain technologies accessible to producers, where they seek less impact and movement in the soil structure, among them, the application to the surface of agricultural corrective products becomes a strategy to mitigate these damages to the soil (Neves Junior et al, 2013) The substantial increase in the levels of exchangeable aluminum in the soil solution can cause several morphophysiological disorders for most cultivated plants (Freitas et al, 2015), mainly affecting the root system, altering or even impeding water and nutrient absorption patterns (Pezzopane et al, 2015;Fidelis et al, 2018). These disorders also manifest deleterious effects on the aerial part of the plant body, such as reduced size and dry mass and Development, v. 9, n. 9, e913997981, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.7981 leaf deformity (Derré et al, 2013).
In addition to choosing the appropriate method, it is important to correct the mineral deficiencies of the soil, in specific cases, the application of limestone and gypsum plays an important role in correcting the acidity of the soil, in addition to providing calcium (Ca), magnesium (Mg) and sulfur (S). Gypsum, which acts in the supply of S, also supplies Ca to the soil-plant system, which allows for a greater export of these elements in the DM of pastures. And this phenomenon is due to the deeper rooting, provided by gypsum that acts as soil conditioner (Mesquita et al, 2002).
In addition to the use of correctives in the pasture recovery process, the use associated with nitrogen fertilization is an important strategy in the production system, since the use of nitrogen is fundamental for the increase in the production of biomass and in the recovery process of pastures (Silva, 2013). The N compound in the soil, resulting from the mineralization of organic matter, does not meet the demand of grasses with high productive potential (Fagundes et al, 2005).
The behavior of N in the soil is dynamic and complex different from other nutrients. It has greater mobility in the soil, undergoes several modifications mediated by microorganisms, has high movement in depth with low residual effect and is lost by volatilization. Therefore, part of the N distributed in the pasture is lost within the system, decreasing its efficiency, due to nitrogen fertilizers being commonly applied in cover, where there is no incorporation into the soil. Two aspects are fundamental in the management of nitrogen fertilization; the source to be used and the installment of the doses, therefore, in order to decrease mainly the losses by volatilization and leaching. This results in a better use of nitrogen by the plant, reduction of losses and maintenance of dry mass accumulation rates (Costa et al, 2010).
Given the above, the work aims to assess pasture recovery with the application of agricultural gypsum associated with nitrogen fertilization.

Climate
The local climate, according to the Koppen classification, is of the Aw type, characterized by the seasons of hot weather in summer and dry winter, with the months from November to March having the highest rainfall. The annual averages of temperature, precipitation and relative humidity are, respectively, 30ºC of maximum, 19ºC of minimum, accumulated rainfall of 1311 mm and average humidity of 78%.

Soil description
The area's soil was classified according to Embrapa (2013). The chemical analysis was carried out in the laboratory of the Faculty of Engineering of Ilha Solteira, of a soil sample collected at a depth of 0-20 cm where the following chemical attributes were determined: P, K, Ca, and Mg the ion exchange resin method, pH in CaCl2, was used; organic matter by calorimetry; H+Al with SMP buffer solution; Al in KCl (Raij et al, 2001). As shown in Table   1.

Experimental design and treatments
The experimental design was randomized blocks in a 3x4 factorial arrangement, that is, absence of nitrogen, 50 kg ha -1 in the form of ammonium nitrate and 50 kg ha -1 urea, interacting with four doses of agricultural gypsum, namely: 0; 750; 1500 and 3000 kg ha -1 and with four replications, totaling 48 plots.

Plant height (PH)
At 120 days after installation of the experiment, the plant height (PH) was determined using a ruler graduated in millimeters, with which six random points were measured per experimental unit. The average of the six points comprised the average height of the plot.

Forage production
At 90 days after the installation of the experiment, manual cuts were made at 15 cm from the soil surface in a sample area of 1.0 m 2 , all material collected in the sample area was weighed immediately and a homogeneous and representative sub-sample was collected that passed through the separation morphological and then dried in an oven with forced ventilation at 65ºC until they reach constant weight, to determine the following variables: total dry mass (TDM); total dry mass of green leafs (TDMGL); total dry mass of yellow leafs (TDMYL); total dry mass of dead leafs (TDMDL) dry mass of culms (DMC); inflorescence dry mass (IDM) and weed dry mass (WDM) was measured by visual sample separation and weighed separately. All variables were converted to t ha -1 by converting the dry mass in relation to the forage weight of the sampled area.

Statistical analysis
All variables were subjected to the F test (p <0.05) and regression analysis was applied to the gypsum doses, where their linear and quadratic models were tested. To determine the best nitrogen source, the Tukey test was applied at a 5% probability of the event occurring.
The point of maximum technical efficiency (PMTE) was obtained through the first order derivative of the quadratic regression equation between the doses where the mathematical model was employed y= -b/2c (Banzatto & Kronka, 2013). The statistical program was used RStudio (R Core Team, 2015).

Results and Discussion
The plant height (PH) was influenced by the application of nitrogen (N), where the Research, Society and Development, v. 9, n. 9, e913997981, 2020 (CC BY 4. to the sources, the use of urea as an N supplier resulted in a higher mean PH when compared to the use ammonium nitrate as shown in Figure 1. Table 2. Mean values and analysis of variance of the regressions where the models were tested: linear, quadratic and cubic, of plant height (PH); total dry mass (TDM); total dry mass of green leafs (TDMGL); total dry mass of yellow leafs (TDMYL) and total dry mass of dead leafs (TDMDL) of forage after cultivation with nitrogen sources and doses of agricultural The relative increase in urea when compared to a control was approximately 13%.
This fact can probably be explained by the higher concentration of N in the composition of urea, which, despite the higher potential volatilization rate presented by this fertilizer, provides a greater amount of N in the easily absorbable soil (Costa et al, 2008).
A statistical difference was observed for the F test in the variables: total dry mass (TDM), total dry mass of green leafs (TDMGL), e total dry mass of dead leafs (TDMDL) as a function of the N application factor. In the vast majority, Pearson correlations were observed between the variables analyzed in the Urochloa humidicola after using gypsum associated with two sources of nitrogen as shown in Figure 2. Research, Society and Development, v. 9, n. 9, e913997981, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.7981 It was possible to observe that the total dry mass (TDM) presented the largest number of positive correlations, this result was already expected, because with the increase in other dry masses, total dry mass (TDM), it is also worth mentioning that larger plants tend to have more dry mass which corroborates these results. It is worth highlighting the positive correlation between TDMDLxIDM, proving that the presence of inflorescence shows that the plants were in the senescence phase, which leads to an increase in the amount of dead leaves in the plant. The positive correlations between the variables evaluated are notorious, as shown in Table 3. Plant height (PH); total dry mass (TDM); total dry mass of green leafs (TDMGL); total dry mass of yellow leafs (TDMYL) and total dry mass of dead leafs (TDMDL). Source: Authors.
Note that for these parameters, with respect to the means separation test, no difference was found for the sources used, however, the absence of N application resulted in lower  Research, Society and Development, v. 9, n. 9, e913997981, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.7981  This is due to the important role of N directly in the metabolism, growth and development of the plant body, being a base component in the synthesis of amino acids, proteins, enzymes, nucleic acid and chlorophyll (Arnuti et al, 2017). According the Farias Research, Society and Development, v. 9, n. 9, e913997981, 2020(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.7981 13 Filho et al, (2018 when the plant's needs for the nutrient are well met, it causes a substantial increase in vegetative development, increasing the size and accumulation of dry matter in the plant body. Also, for the parameter total dry mass (TDM) as shown in Figure 6  The best performance of the pasture when cultivated in the presence of gypsum is presumably due to the beneficial effects of using it, among them the supply of S in the deeper layers, better root development, leaching of toxic elements (Fe 3+ , Mn 3+ , Al 3+ ), which improves the availability and absorption of bases, among others (Amaral et al, 2017). For research purposes and understanding of dynamics, higher doses of ammonium nitrate should be tested under the same study conditions, allowing a better understanding of the biological curve. Ammonium nitrate has less use in relation to urea due to its higher price, but it may prove to be advantageous in the production field as it presents greater efficiency and reduced volatilization and leaching losses (Balbinot Junior et al, 2019).
For the variables culms dry mass of (CDM) (Figure 7) and inflorescence dry mass (IDM) (Figure 8), a statistical difference was determined for the sources of N, where the results for treatments without fertilizer application showed lower (p≤0.01) ( Table 4). There were no differences between the sources for them. This fact explains the importance of nitrogen fertilization in agricultural systems as an indispensable practice when seeking to obtain high yields, regardless of the applied source, provided that it is carried out consciously and with a theoretical basis.
The CDM was also influenced by the application of gypsum doses, and, by studying the interaction (Figure 7), the polynomial behavior obtained was of quadratic adjustment for urea, linear for ammonium nitrate and not significant for the absence of application. For the use of urea, the data denote a PMTE of 1730.7 kg ha -1 resulting in 2.38 t ha -1 of culms dry mass of (CDM). The maximum dose for this variable corroborates that for total dry mass (TDM). Aiming at the maximum production of the study, the culms dry mass of (CDM) represents 47.9% of the total dry mass of the pasture.
The observed event can be elucidated by the increase in the number of tillers per area and the greater weight of tillers. With the increase in stalk weight, the tillers become more developed, as a way to guarantee the support of the leaves (Santos et al, 2009).  Source: Authors. Development, v. 9, n. 9, e913997981, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.7981 16 No statistical difference was found for the variable weed dry mass (WDM), for any factor under study. Possibly, the beneficial effect of the practice of fertilization had a more accentuated effect on the pasture, accelerating the muffling effect in relation to the invaders (Crusciol & Borghi, 2007), which did not show a more developed, hesbistatic or hermetic behavior.

Final considerations
The use of urea as a source of N resulted in a higher plant height (PH) when compared to the use of ammonium nitrate, representing a relative increase of approximately 12% in relation to the control.
Dose of 1730.8 kg ha -1 of agricultural gypsum resulted in a maximum production of 4.97 t ha -1 of dry pasture.
The linear interaction of the use of ammonium nitrate with gypsum doses shows an extremely interesting synergistic potential with this source.
For dry mass of culms (CDM), the use of urea had a PMTE of 1730.8 kg ha -1 of agricultural gypsum resulting in 2.38 t ha -1 .
The culms dry mass of (CDM) represented 47.9% of the total dry mass of the pasture.