MILHO VERDE CULTIVADO EM DIFERENTES ESPAÇAMENTOS, DESFOLHAS E ÉPOCAS DE SEMEADURA

Abstract

“Green corn” (slightly immature corn) is a culture of great social, cultural, and economic importance. This study aimed to evaluate the agronomic performance of AG 1051 cultivar, subjected to three sowing periods (I, 9 Jun. 2017; II, 12 Aug. 2017; and III, 17 Dec. 2017), four different spacings (0.60, 0.70, 0.80, 0.90 m), and four types of defoliation (removal of all leaves above the ear of corn (AA), removal of all leaves below the ear of corn (ABC), removal of two leaves below and two leaves above the ear of corn (TBTA), and lastly the control, without removing leaves (CONTROL), with four replicates and a 3x4x4 factorial scheme. The leaves were removed in the phase VT. Seed treatment was carried out using Fludioxonil+Metalaxyl-M (Maxim XL) fungicide and thiamethoxam-based insecticide (Cruiser 600 FS), both with a dosage of 200 mL per 100 kg of seed. S-metalachlor (Dual Gold 915 EC) herbicide at the dose of 2 L ha-1 and Atrazine (Atranex 500 SC) herbicide at a dose of 5 L ha-1 were applied in preemergence weed control. Tembotrione (Soberan) at a dose of 200 mL ha-1 was applied in post-emergence weed control. In all sowing periods, 16 kg ha-1 of N, 120 kg ha-1 of P2O5, and 40 kg ha-1 of K2O were applied. The cover fertilization was carried out with 180 kg ha-1 of nitrogen (urea) in the phase V5. Pest and disease control were carried out according to the technical recommendations for the crop. Plants were irrigated via central pivot in the first two sowing periods. There was no irrigation in the third sowing period, accounting only the water coming from precipitations in that period. Irrigation management was done using the Class A tank. The corncobs diameter with straw (CDS), the corncobs diameter without straw (CDW), corncobs length without straw (CLW), number of commercial corncobs (CC>15), number of non-commercial corncobs (CC<15), number of grain rows (NGR), number of grains per row (NGpR), corncobs yield with straw (CYS) (kg ha-1 ), corncobs yield without straw (CYW) (kg ha1 ), mass yield (MY) (%), and dry matter content (DM) (%) were evaluated. The harvest of the sowing periods I, II, and III was carried out on 23 Sept. 2017, 11 Nov. 2017, and 3 Mar. 2018, respectively. The corncobs were harvested from the two central rows of each treatment, excluding 0.50 m of border. Approximately 50 g of fresh samples were weighed for determining the dry matter, and they were placed under forced ventilation oven at 65ºC until obtaining constant weight. All data were submitted to analysis of variance using the F-test. The means of the sowing periods and the defoliation types were compared by the Tukey test at the 5% significance level, and the spacing means were submitted to the regression analysis. All analyzes were carried out using R software. There was a significant effect of sowing period for the CDS, CDW, CLW, NGR, NGpR, and CC<15 variables. The sowing period II stood out from other periods in the CDS and CDW. In the sowing period III, longer corncobs (CLW) were produced, and NGR and NGpR were higher in the sowing periods II and III. The greatest number of non-commercial corncobs (CC<15) was produced by plants sown in period I. Defoliation was significant for CDS, CDW, CLW, and CC<15. It was verified that the plants without defoliation presented higher values for CDS, CDW, CLW, and was found that the plants showed decrease in the averages evaluated, regardless of the defoliation type. The defoliation of AA showed a greater number of CC<15, superior to the other defoliation. The interaction between sowing period and defoliation was significant for CC>15, CYS, CYW, and DM. The treatment without defoliation for CC>15 in sowing period III was superior to the others. There was no difference among the periods for AA defoliation. In the defoliation of ABC and TBTA, plants sown in period III showed the highest numbers of commercial corncobs. Regardless of the defoliation carried out in sowing period I, there was no difference in the plants production of CC>15. The plants with no defoliation (CONTROL) showed the highest CC>15 in the sowing periods II and III. The sowing period II stood out with the highest CYS in the CONTROL, AA, and ABC treatments. In the TBTA defoliation, the sowing periods were statistically the same. When evaluating sowing period I individually, it was found that the treatments did not differ among themselves, regardless of the defoliation type. The same behavior occurred in sowing period II. In sowing period III, the plants without defoliation (CONTROL) showed the highest yield. The CYS with a significant difference spacing of 0.60 m among rows showed higher yields. CYW was higher in CONTROL, AA, and ABC treatments in the sowing period II. For TBTA defoliation, there was no significant difference among the sowing periods. When evaluating the defoliation types at each sowing period, it was found that in the sowing period I, regardless of the defoliation, the CYW did not differ. Plants that did not have the leaves stripped showed higher CYW in the sowing period II. CONTROL, ABC, and TBTA treatments were also superior to the AA treatment in the sowing period III. The spacing among rows was significant for CYW, showing higher averages in 0.60 m spacing. The DM contents in the CONTROL, AA, ABC, and TBTA treatments were higher in the sowing period II. They were inferior and did not differ among themselves in the sowing periods I and III. There was no difference among defoliations during the sowing period I. The highest DM content was for AA defoliation in the sowing period II. There was no difference among defoliations in the sowing period III, similar to the sowing period I. The corncobs mass yield (MY) was influenced by the interaction among the sowing periods and spacings. The sowing period II showed the highest mass yield at all spacing. When evaluating the sowing periods I, II, and III individually, it was found that spacing did not differ from each other. The spacing of 0.75 m provides higher MY. The spacing of 0.60 m provides greater corncobs yield with and without straw. The AA defoliation decreases CDS and CDW, the CLW, the CYS in the sowing period III, the CYW in the sowing period II and III and increases the CC<15. The sowing period II promotes higher CYS and CYW.