Yield parameters of two maize hybrids submitted to different spacing in Paraibano Semiarid, Brazil

— One of the most important crop practices to obtain high grain and forage yields in maize is the correct management of the seeding density, because the plant stand can influence growth components, production and partitioning of photoassimilates. The objective of this study was to evaluate the growth and yield of corn cultivation at five spacings, using two hybrids. The experiment was installed at the experimental farm of the Federal University of Campina Grande, CCTA/UFCG, Campus de Pombal, located in the city of Santo Domingo — PB. The experimental design was a randomised complete block, in a factorial scheme, with the factors being five spacings and two hybrids, with four replications. The spacings were 0.15, 0.30, 0.45, 0.60 and 0.75 m between plants, and the two hybrids were ‘AG - 1051’ and ‘BR - 106’. The following yield components were evaluated: ear weight with straw and without straw; weight of 1000 seeds, ear length and diameter, grain yield and mass of corn. The spacings of 0.30 and 0.45 m had the best results, corresponding to the population densities of 30,000 and 40,000 plants ha -1 , and the ‘AG - 1051’ cultivar had the best performance, with an average yield of 13 t ha -1 , largely due to its better genetic load.


I. INTRODUCTION
Corn (Zea mays L.) is a monocot the Poaceae family, native to Central America, and it is among the most cultivated cereals consumed in the world, due to production potential, chemical composition, nutritional value, multiplicity of applications and high adaptability, which facilitate cultivation beyond the broad market [12].
Among the various factors that may interfere with the productivity of the corn, seeding density and arrangement appear to be the main factors responsible for the low yield of corn in Brazil [13]. This is because the plant stand can affect the growth of the culture components due to increased competition in assimilate partitioning [2]. The ideal population to maximise the yield of corn grain ranges from 30 to 90 thousand ha -1 plants, depending on the availability of water, soil fertility, sowing and spacing adopted among rows and among plants in the cultivation line in addition to cultivating characteristics, which are crucial to plan the density of plants [8].
According to [14], studies indicate that modern hybrids have had a reduction in spacing from 0.9 to 0.4-0.6 m, and an increase in the population of plants 60 to 75 ha -1 plants. [17] showed that plant populations between 60 and 80 thousand plants ha-1 showed increases in productivity of approximately 12.5 to 13.6%, corresponding to spacing between plants in the row of 0.6 and 0.8 m. The use of higher plant densities in smaller spacing allows greater interception of photosynthetically active radiation, promoting higher grain yields per plant [15].
According [19] the management of plant density is one of the cultural practices that most interferes with the productivity of maize. This response is associated with the fact that maize does not have an efficient space compensation mechanism, since it tends little and has low prolificacy and limited expansion capacity. The effects of density are also reflected in genotype hybrids with smaller numbers of leaves that are upright, with lower biomass production, which reduces the interference of one plant with another [9].
Considering the importance of obtaining high yields and knowledge about the double spacing recommendations between rows of commercial hybrids, this work was to evaluate the influence of five spacings cultivation, growth and productivity of two hybrids of commercial corn. Soil preparation was done by cross harrowing five days before sowing, favouring the initial weed control as well as providing conditions for a good germination and root growth of commercial culture.
Before sowing, soil sampling data was collected at a depth of 0-0.20 m and sent to the Soil and Plant Nutrition Laboratory, LSNP, at the Centre for Science and Agrifood Technology at the Federal University of Campina Grande, to determine its physicochemical characteristics and preparation of fertiliser recommendations (Table 1 and 2).  The fertilisation was performed during the period of sowing, and 10, 60 and 20 kg ha -1 of nitrogen, phosphorus and potassium, respectively, were applied in the groove. After 30 days, 20 kg ha -1 of nitrogen was applied to cover. The sources used were superphosphate, potassium chloride and urea fertilisers.
The seeding was performed manually in open grooves with the aid of spades; the spacing used was 0.8 m between the double rows and 0.30 m between the single rows. Each plot consisted of three double rows, with different plant densities in planting lines according to the treatments employed. Thinning was performed at the V3 stage, when the plants had three fully expanded leaves.
The treatments consisted of two corn hybrids ('AG-1051' and 'BR-106') and five approximate density values: The management of the weeds was conducted by means of chemical control associated with manual hoeing undertaken only as post-emergent application in the association of herbicides (Atrazine + Nicossulfurom) at a dosage of 1.5 to 5 L h -1 , respectively, which are recorded in the MAP (Ministry of Agriculture Livestock and Supply) and are selective for the corn crop.
Based on the water requirement of 800 mm culture during the cycle, irrigation was handled to provide a sheet of 6.7 mm/day/plot, since both hybrids have an average cycle of 120 days. The irrigation system was with 20 mm thick dripping tapes with self-compensating drippers, and the dripping tapes were coupled to spiders, which were arranged in 32 mm tubing, in a single line, in the experimental area.
Throughout the crop cycle data on precipitation and temperature were monitored. According to INMET (2017), one 206 mm rainfall during the experiment was observed as well as an average temperature of 28°C (Fig. 1).

International Journal of Advanced Engineering Research and Science (IJAERS)
[  Harvest was done manually at 127 OF before the physiological maturation stage R6, with the particular components of the production cultureof ear weights with and without straw (kg ha -1 ), number of grains per spike (kg ha -1 ), diameter of shank (mm), ear length (cm), weight of 1000 seeds, seed yield (kg ha -1 ) and cob weight.
Data were subjected to analysis of variance by F (p ≤ 0.05) test, when significant effect was verified the treatment means were unfolded, and regression analysis was applied to the density factor, and for the hybrid factor. All statistical procedures were performed using the computer program for statistical analysis SISVAR [7].

III. RESULTS
The interaction between hybrids and different spacing did not influence all variables (Table 3). Evaluating the effect of different spacings, we observed a significant effect on the straw with ear weights (PES/P), the ear weights without straw (PES SP) and numbers of grains per spike (Nº GR ESP). For hybrid sources of variation, there was no significant effect for the studied variables, except for PES/P.  Fig. 2A, 2B and 2C). The spacings above 0.45 m (0.60 and 0.75 m) did not promote significant increases for variables of these hybrids. The values of the straw with ear weight corroborate those obtained by [16] that when evaluating the hybrid 'AG-1051', aimed at

International Journal of Advanced Engineering Research and Science (IJAERS)
[ Vol-7, Issue-2, Feb-2020]  https://dx.doi.org/10.22161/ijaers.72.38  ISSN: 2349-6495(P) | 2456-1908(O) www.ijaers.com Page | 286 The interaction between hybrids and spacing influence (p < 0.01) the weight of 1000 seeds (P 1000). The length of the spike (C), grain yield (PG) and mass cob (MSAB) were affected (p < 0.01) by treatment alone (Table 4). Based on these results, we can infer that the seeding density was not a determining factor for there to be changes in the variables P 1000. The length of the spike (C) increased linearly at the rate of 5.680 cm for each meter (m) increment, considering all studied spacings (Fig. 3A), with a maximum of 15.768 cm in spacing of 0.75 m.   [18] noted that dehusked ear weight and number of grains per spike showed higher average values when the corn was cultivated under larger spacings (0.83 and 1.00 m), assigning the highest weights to less competition for abiotic factors, such as water, sunlight and nutrients and hence the greater potential for expression of genetic potential. [6] to evaluate the performance of corn cultivars for the production of corn found significant differences among cultivars, for ear weight variables and dehusked ears, with an average of 253.12 and 190.29 g, respectively.on the importance of the work or suggest applications and extensions.

IV. DISCUSSION
As the spacing is an alternative to increase the interception of solar radiation, as well as a better photosynthetic activity and proper allocation of assimilates, depending on other management factors such as irrigation, the plant can not only reduce the average ear weight values, but also other factors such as the number of grains per spike [18], [5]. [20], who studied the performance of corn hybrids in different spacings, had higher mean values for the variables of the shank length and number of grains per spike, as it increased the spacing between plants.
The delay in processing the lateral branches of spike early observed in cultures denser, can affect the final number of grains per spike and the morphological and physiological changes imposed on the female inflorescence before flowering, during fertilisation and early grain filling. The number of grains per spike at high densities can also be reduced by the abortion of newly fertilised eggs in the early part of grain filling, occurring more frequently in localised grains in the apex of the ear, which are the last to be fertilised [9]. [3], when evaluating the production potential of several hybrids in different spacings, observed that there was no significant difference for the weight of 1000 grains.
The maximum observed values of grain and cob weights in plots spaced at 0.45 m and 0.44 m, respectively, was 10.74 Mg ha -1 and 0.31 g. The results, possibly because there were larger gaps and therefore less plant population, potentiating the photosynthetic capacity of the plants, and the C4 metabolism that makes them highly efficient in converting light energy into chemical energy, allowing more significant yields and better utilisation of the available radiant energy, as a result of the equidistant distribution of plants. [4] found that the grain yield was influenced by the double line spacing (0.20 × 0.70 m).
[11] studied different populations of plants (40, 53, 71, 84 and 97 thousand ha -1 plants) observed linear productivity, as the plant density increased, for some hybrids. The authors concluded that the increase in grain yield, with increase in plant density, depends on the hybrid being worked.

V. CONCLUSION
The combination of 0.8 m spacing between the double rows, and spacing of 0.45 m between plants in the row corresponding to a population of approximately 40.000 h-1 plants showed promise for achieving high productivity. We analysed two different hybrids, and for most of the observed variables, the results obtained increased with increased spacing and decreased from 0.45 m spacing between plants.