Residual Effect of Gypsum and Phosphate Fertilization on the Second Corn Crop

The objective of this study was to evaluate the residual effect of the gypsum when used with phosphate fertilization on the mineral nutrition, development and yield of second corn crop. The experiment was conducted at UFJ, with an experimental design consisting of 15 treatments established in randomized blocks in a 5 × 3 factorial scheme, with 4 replicates. The first factor corresponded to doses of gypsum (0, 1, 2, 4 and 8 Mg ha) and the second factor corresponded to doses of phosphorus (0, 40 and 80 kg ha). 16 months after the application of the various doses and treatments of agricultural gypsum, the following components were evaluated: dry root mass, macro and micronutrient contents in the leaves, production components and grain yield. The residual effect (16 months) of gypsum did not increase efficiency of phosphate fertilization for second corn crop. Under water stress conditions, the yield of corn grains responds to the application of agricultural gypsum above that of the dose recommended by the formula NP = 5 × g kg of clay, which for this research is 2.93 Mg ha of gypsum. Phosphorus provides increases in corn grain yield only when 100% of the recommended dose is applied.


Introduction
The cultivation of plants and the raising of livestock are complementary and elementary activities for the growth of a region.In this context, the corn crop (Zea mays) is of great importance.With this, the small crop or second corn crop of the year, known locally in Brazil as milho safrinha, which is sown from January to March, stands out as one of the main grain crops produced in Brazil, mainly in the South, Southeast and Center West, being sown immediately after the soybean harvest (CONAB, 2017).
Due to the time it is sown, the second corn crop often faces periods, sometimes long, of water stress.Therefore, the management of the soil in areas where the cultivation of this crop is common must provide optimum conditions for the full root development of corn, especially in terms of depth, since this practice will allow farmers to take advantage of a greater volume of soil, and consequently, a greater access to water and nutrients, focusing on those with low mobility or soil with the correct properties such as that with phosphorus (P), for example.
Among the main factors of the soil that limit the full development of the root system of agricultural crops are those of a physical nature, such as compaction, reduction of porosity and soil aeration, as well as those of a chemical nature, such as an excess of aluminum (Al 3+ ) and the low levels of calcium (Ca 2+ ) and P in subsurface.
Liming has long been the main tool for the correction of acidity and the supply of Ca 2+ and Mg 2+ to the soil, but in established no-till farming areas, the application of this corrective process is limited to the soil surface since excessive soil disturbance is avoided when liming.Thus, the benefits of liming are mostly restricted to the first few years and to the surface of soil, and therefore, does not solve the subsurface acidity problems.
Thus, the application of soil conditioners, such as agricultural gypsum, due to its greater solubility, reduces Al 3+ activity and increases nutrient availability in the deeper layers of the soil (Ritchey, Silva, & Costa, 1982).The combination of agricultural gypsum with liming may favor root development at greater soil depths, especially in jas.ccsenet.

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Materia
The exper year 2015/ 17º55′32″ The predo dry and c classificati n the area was the area had be g no-till farmin rch with its tre y year in whic crops: soybea 5 and h the e, 16 months after the application of gypsum, the corn sown in the second crop of 2015/2016 was in fact the fifth crop cultivated.
The treatments related to P 2 O 5 received fertilizers to increase productivity of soybean and second corn crop at their respective doses, which were 0, 50 and 100% of the recommended dose of P 2 O 5 .
For the chemical and textural analysis of the soil before the research, 10 simple soil samples were collected, before the 2014/2015 harvest, with the aid of a probe to compose a composite soil sample of the soil layers 0-20 and 20-40 cm deep (Table 1).Since it is an experiment in which the effects of the treatments have been evaluated over time since the beginning of the first crop of the agricultural year of 2014/2015 and that the chemical analysis of the soil is always carried out after the harvest of the second corn crop, the soil's chemical analysis performed after the harvest of the second crop of the year of 2015 have also been presented in table 2 for a better explanation of the data.
The experimental design consisted of 15 treatments established in randomized blocks, in a 5 × 3 factorial scheme, with four replications, with each plot measuring 11.25 m 2 (2.25 × 5 m).The first factor corresponded to the doses of gypsum (0, 1, 2, 4 and 8 Mg ha -1 ), and these doses represent 0, 34, 68, 136 and 273% of the recommended dose according to Sousa and Lobato (2004).The second factor corresponded to the doses of phosphorus (0, 40 and 80 kg ha -1 of P 2 O 5 ) representing 0, 50 and 100% of the recommended dose.
For soil correction 3.0 Mg ha -1 of dolomitic limestone (85% PRNT) was applied relying soley on gravity to penetrate the soil 3 months before sowing the soybean crop in the agricultural year of 2014/2015.The gypsum was applied only once 30 days after the limestone in each treatment's respective doses and since then the area had been cultivated every year with a rotation of soybean and corn intercropped with brachiaria.Only the residual effect of the applied gypsum in a combination with phosphate fertilization was evaluated from the first year being carried out at the time of sowing of each crop in all agricultural years.The chemical makeup of the gypsum used in this research is shown in Table 3.The recommended doses of N, P and K for a high yield of corn were 150 kg ha -1 of N and 80 kg ha -1 of P 2 O 5 and K 2 O.The sources used were urea, triple superphosphate and potassium chloride, respectively.The P 2 O 5 was distributed at sowing time in the furrow at the doses for each treatment.It is important to note that for the crops prior to the second corn crop the same doses of P 2 O 5 were used.N and K were manually distributed in each plot.
For N, the applied urea doses were 30 kg ha -1 at sowing and 120 kg ha -1 when the crop was at the V3-V4 stage.
The first and second applications of K 2 O were carried out at 15 and 25 days after sowing with doses of 60 and 20 kg ha -1 of K 2 O, respectively.
The sowing of the hybrid corn AG-8677 PRO 2 was carried out on February 23, 2016, using a 5 row planter tractor distributing 2.8 seeds per meter.Each plot was composed of 5 rows of 5 meters, the area of use being the 3 center rows with 0.50 m excluded from each end.Corn seeds were treated industrially with deltamethrin.
With the objective of controlling invasive plants, a dose 1.5 L ha -1 of commercial atrazine and 1.5 L ha -1 commercial glyphosate was applied during the V3-V4 stage.In order to control Spodoptera frugiperda (fall armyworm), two applications were made with the products Bulldock® 125 SC (beta-cyfluthrin) and Connect® (imidacloprid and beta-cyfluthrin), with 0.1 L ha -1 and 0.75 L ha -1 , respectively.
Weed management was performed with a post-emergence application of 2.5 L of glyphosate and 1.5 L of atrazine ha -1 for the control of unwanted soybean plants.Two preventive applications of fungicides with the product Approach Prima (0.3 L ha -1 ) were applied for disease management.Pest control was performed with insecticide based on the level of weed control in the area using the products Bulldock 125 SC (0.1 L ha -1 ) and Connect (0.75 L ha -1 ).
At the time of the female inflorescence (silking), 5 leaves were collected per plot, opposite and below the first ear, excluding the central vein, to determine macro and micronutrient leaf contents according to Martinez et al. (1999).The leaves were kept in an oven at 60 ºC until it had a constant mass.The dry leaves were then sent to the Laboratory of Analysis of Soils and Vegetable Tissue of the State University Paulista (UNESP) "Júlio de Mesquita Filho" Ilha Solteira Campus for determination of macro and micronutrient contents according to methodology described by Malavolta et al. (1997).
Root samples were collected before harvesting the corn, where three soil samples were collected, randomly distributed within the area of use of each plot in the middle of the betweenlines, that is, 22.5 cm away from the planting lines, in the soil layers 0-20 and 20-40 cm in depth.For this operation, a probe was used which is capable of collecting a volume of 0.922 liters of soil for every 20 cm of depth.After the collection, with the aid of a sieve and running water, the soil and roots present in the sample were separated.
Subsequent to the separation, the collected root samples were left in a forced air circulation oven at 60 °C until the plant material had a constant mass, to be weighed to quantify the mass of dry roots in each plot.Subsequently, the dry root mass values obtained were corrected to a standard volume of 1.0 dm-3 of the initial soil sample.
At harvest time (07/13/2016), the ears present in the area of use of each plot were collected manually and stored in bags with the identification of their respective plots.Ten ears were randomly assigned to each plot to determine the dry mass of the ear, the number of rows of grain per ear, the length of the ear, the diameter of the ear, as well as, the diameter of the cobs.By subtracting the last two parameters and then dividing the result by two the average grain length was calculated.
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Results
The summ shown in T macronutr Ca 2+ and regression   (2007), evaluating the DRM in many soil layers noted that in the presence of gypsum the dry root mass values tend to decrease in the 0-10 cm layer of soil and increase in layers deeper than 10 cm.Different results were found by Rosolem e Marcello (1998), who observed that the low availability of P, induces root growth in terms of length with a consequent increase in surface area of the root, but without increasing dry root mass.
In the interaction between gypsum and phosphorus there was an increase in the dry root mass of corn with the increase in the availability of P only in the 20 to 40 cm layer of soil and only for the dose of 8, 0 Mg ha -1 of gypsum (Table 8).
The summary of the variance analysis (F-Test) for corn production components is shown in Table 9.There was no interaction between the factors studied (G × P) for any of the evaluated production components.For the P 2 O 5 dose variation factor, only ear diameter and number of rows presented different behavior out of the doses evaluated (Table 9).
For ear diameter, the treatment that did not receive phosphate fertilization presented lower values in relation to the others.For the number of rows per ear, there was a significant difference only between treatments 0 and 80 kg ha -1 of P 2 O 5 (Table 10).These components exhibit a relationship of dependency with each other, since the increase in the number of rows usually results in ears with larger diameter.Note.The averages followed by the same letter do not differ statistically from each other using the Tukey test at 5% probability. jas.ccsenet.
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Table 1 .
Chemical and textural analysis of the soil at 0-20 and 20-40 cm depths of the experimental area before carring out the experiment in 2014, Jataí,GO, 2018

Table 3 .
Chemical composition and moisture of the agricultural gypsum used in the experiment.Jataí,GO, 2018

Table 10 .
Average ear diameter, number of rows and productivity, evaluating the doses of phosphorus in isolation