Nitrogen in corn and sunflower

Essential for the growth and development of corn and sunflower plants, the Nitrogen is extremely important for both crops. That's why the importance of determining the fertilizer doses of this element in a balanced way, that at the same time prioritize aspects of productivity are also economically viable.

As agriculture becomes more competitive production cost at its various levels of technology becomes an important instrument in the administration’s decision-making process rural, although there are difficulties in estimating them (MARTIM et al., 1994).

Confresa is the most populous municipality from the region called Araguaia – Xingu, located northwest of Mato Grosso. This one municipality is part of the transition between the Cerrado and Amazon Forest Biomes, between the 10th to 11th parallels and the 51st to 53rd meridians. With 24.293 inhabitants (IBGE, 2012), the municipality's population is distributed 34,80% in the urban area and 65,20% in the countryside.

According to Zanatta (2013), the municipality of Confresa “grows” above the national average in demand for credit and at a pace business in the cultivation of soybeans and corn, in an integrated manner with livestock farming, as well as such as the construction of gigantic warehouses to store grain production. Banco do Brasil, for example, increased its rural “businesses” by 2.000% in last five years.

Logistical problems such as price freight, unfinished highways and roads and/or in poor condition, low fertility of soils occupied for years with pastures without corrective input and fertilizers and lack of production storage structures influence the components of production costs.

The growth of agricultural areas cultivated in the municipality of Confresa therefore demands economic studies to that farmers, agriculturalists and economic groups operating in the sector agriculture can understand more concisely the geotechnical factors and that influence, in some way, on the quantitative participation of the components of the production cost of that municipality. This way, they can provide a better basis when planning important actions to obtain the profits.

Nitrogen (N) is essential for the growth and development of plant species, as present in the composition of the most important biomolecules, such as ATP, NADH, NADPH, chlorophyll, proteins and numerous enzymes (MIFLIN & LEA, 1976; HARPER, 1994; MARSCHNER, 1995; MALAVOLTA, 2006).

The low efficiency of fertilizers nitrogen is related to the degree of recovery of this element by plants, reaching in many cases less than 50%, due to leaching, ammonia volatilization, denitrification, erosion and microbial immobilization (BREDEMEIER & MUNDSTOCK, 2000; CHAVARRIA & MELLO, 2011). Associated with These factors also include the high cost of nitrogen fertilizers (DÖBEREINER, 1990). At the In the case of corn, for example, N is the most expensive nutritional element in the culture production system (CANTARELLA & MARCELINO, 2008).

The maximum economic dose of fertilizers can be understood when the value of the increase in production is equal to the cost of fertilizer, with a proportional increase in fertilizer will not be paid for by the monetary increase in production (RAIJ, 1991).

The technician's guidance in this case is the law of proportions variables, also called the law of diminishing returns or the law of non-proportional increases, which can be stated as follows: if the amount of a productive factor is increased by equal increments, while the quantities of other factors, the corresponding increases in production may increase at first, but will decrease after a certain point (ZAGATTO & PIMENTEL GOMES, 1960).

The objective of this work was to estimate the doses of maximum economic nitrogen applied by broadcast, covering corn plants and sunflower grown in the 2015 and 2016 "safrinhas" in Confresa, Mato Grosso Brazil, Brazil.

The experiment was conducted at the Federal Institute of Education, Science and Technology of Mato Grosso – campus Confresa, in an area previously cultivated with soybeans. Corn (Down AgroSciences Power Core 22M12VIP) and sunflower (M734) were sown respectively in February and March, on the dates 26/02/2015 and 11/02/2016 and 28/03/2015 and 27/03/2016 with a spacing of 0,50 cm between lines, establishing a final population of 3,1 plants per linear meter and 4,0 plants per linear meter. The amount of fertilizer supplied in response to fertilization with P2O5 and K2O was carried out considering the values ​​of the soil chemical analysis and the recommendation of fertilization for these crops according to Ribeiro et al. (1999). Still, on the line of sowing, 25 kg/ha of N were added.

The experimental design used was randomized blocks with supply of 0,0 20,0, 40,0, 60,0 80,0 and 100,0 kg/ ha of nitrogen released at the V6 phenological stage for corn and sunflower using urea and four repetitions.

The estimated productivity in kg/ha of corn or sunflower grains adjusted to humidity of 14% (evaluated characteristic) allowed the determination of maximum production N dose (DNMP) and maximum economic nitrogen dose (DNME) through regression equation 2nd order polynomial as described by Raij (1991). To this end, they were also considering the sales values ​​of R$19,00 (2015) and R$32,75 (2016) and R$47,00 (2015) and R$47,00 (2016) for bags of corn and sunflower grains with 60 kg respectively, as well as the kg value of N in the nitrogen source used of R$ 2,44.

In trials with corn and sunflower, an increase was observed of net profit and gross revenue with an increase in N doses in the cultivation of corn and sunflower to a certain "point", and that the increase in the cost of fertilizer is linear.

The nitrogen dose of maximum productivity (DNMP) average in corn obtained through the derivatives of the regression equations in harvests of 2015 and 2016 respectively was 53,82 kg/ha of N added in top dressing, allowing productivity average of 116,08 bags of grain corn/ ha. Furthermore, in this sense, the average maximum economic nitrogen dose (DNME) was 48,13 kg/ha of N providing average productivity of 115,69 bags of corn grains/ha. The average difference between DNMP and DNME for corn was 5,69 kg/ha of N, which means that the DNME was 10,57% lower than the DNMP.

Silva et al. (2014) working with doses of N (20% in the sowing line and 80% in the broadcast) and phosphorus in corn cultivation "safrinha" (19/03/2010) with use of irrigation in summers in a Cambissolo Eutrophic clayey texture in the city of Baraúna, Rio Grande do North, observed that 88 kg/ha of N allowed maximum productivity of corn grains, with the maximum economic dose being 70 kg/ha of N combined with 120 kg/ha of P2O5., a difference of 41,67%.

Pavinato et al. (2008), cultivating corn in harvests 2002/2003 and 2003/2004 in a dystrophic Red Oxisol found that maximum corn grain productivity under sprinkler irrigation occurred with 283 kg/ha to 289 kg/ha of N, but maximum economic efficiency occurs at 156 kg/ ha 158kg/ ha  of nitrogen. That also means a respective difference of 44,87% and 45,33%.

Orioli Junior et al. (2011) conducted an experiment aimed at producing corn grains in the municipality of Ribeirão Preto, São Paulo, in dystroferric Red Oxisol clayey texture. Increasing doses of N were applied in coverage, in the However, 20 kg/ha of this element were used in the sowing line. To the maximum economic doses and maximum productivity of corn grains were 150kg/ha and 170 kg/ ha and 136kg/ha and 162 kg/ ha of N with respective use of urea and ammonium sulfate, which results by 9,33% and 4,71% respectively.

The nitrogen dose for maximum productivity (DNMP) sunflower average obtained through the derivatives of the regression in the 2015 and 2016 harvests, respectively, was 69,94 kg/ ha of N added in coverage, allowing an average productivity of 29,29 bags of corn grains/ha. Furthermore, in this sense, the maximum nitrogen dose economic (DNME) average was 61,88 kg/ ha of N providing average productivity of 29,08 bags of corn grains/ha. The average difference between DNMP and DNME for corn was 8,06 kg/ha of N, which means that the DNME was 11,39% lower than DNMP.

Rasool et al (2013), in silt soils of Kashimira, identified in two years of studies maximum economic doses and maximum productivity of 80,00 kg/ha and 120,00 kg/ha N. Süzer (2010) in silty soils in Turkey identified in three years of studies with different populations of hybrid plants of sunflower, average doses of maximum economic and maximum productivity of 50,00 kg/ha and 60,00 kg/ha N respectively. Rasool et al (2013), in silt soils of Kashimira, identified in two years of studies maximum economic doses and maximum productivity of 80,00 kg/ha and 120,00 kg/ha N.

In Cassilândia, Mato Grosso do Sul, Biscaro et al. (2008) tested four increasing doses of N divided into three coverages in Quartzarenic Neosol under irrigation, from March to August. They found that 55,00 kg/ha of N provided the highest grain productivity. Sachs et al. (2006) stated that with this same value they obtained the best response on the productivity of sunflower achenes. In the experiment of Santos et al. (2013), from April to August in Lagoa Seca, Paraíba, testing increasing doses of N in two coverage installments, they found that the dose of maximum productivity of sunflower achenes was 112,43 kg/ha of N.

In an experiment conducted in the municipality of Londrina, Paraná, in a eutrophic Purple Oxisol, very clayey texture during three harvests (1991/92, 92/93 and 93/94), Castro et al. (1999) observed in the joint analysis of data relating to sunflower cultivation using urea in incorporation or part incorporated (30% of the total N in the tested dose) and part in coverage, that the dose economic maximum was 17,5 kg/ha of N, and it is not possible to determine a "point" in the second order polynomial equation to determine the dose of maximum grain productivity.

Conclusions

The average doses of N supplied to "throw" on the cover of the corn and sunflower plants in which they were The maximum grain yields obtained were 53,82 kg/ha and 69,94,00 kg/ha N respectively, being 48,13 kg/ha and 61,88 kg/ha N the maximum doses economic.

The maximum economic N doses were respectively lower by 10,57% and 11,39% in relation to doses of N used to obtain maximum productivity of corn grains and sunflower.

Article published in issue 222 of Cultivar Grandes Culturas, November, 2017.