Evaluation of NPK doses on the production of papaya

The study aimed to evaluate the effect of different NPK doses on the yield components of papaya hybrid ‘Caliman 01’. The experiment was carried at the company WG Fruticultura, located in the Chapada do Apodi region. Five nitrogen doses (94, 590, 837, 1088 and 1575 kg N ha-1), five phosphorus doses (10, 72, 96, 133 and 195 kg P2O5 ha -1) and five potassium doses (75, 527, 752, 978 and 1429 kg K2O ha -1), were combined according to the experimental matrix Pan Puebla II, in 16 combinations and distributed in a randomized block design, with five repetitions. The plots consisted of six papaya plants and the four central plants were evaluated. The fertilizers urea, monoammonium phosphate and potassium chloride were used as NPK sources, respectively. The doses of N and K were split into 30 applications, one every two weeks. Phosphorus doses were split into two applications, the first at 75 days after transplantation (DAT) and the second one at 150 DAT. Fruit production was evaluated during eight months. The best results were obtained for NPK doses of 1088, 72 and 527 kg ha -1, respectively. Increasing N doses linearly increased the number of fruits per plant and yield, while increasing P and K doses reduced yield by a quadratic and linear model, respectively. The combination of NPK doses 590-72-75 kg ha-1 provided the best economic results with the highest rate of return for papaya production.


INTRODUCTION
Brazil presents excellent climatic conditions for the cultivation of papaya. In 2016, Brazil produced 1.4 million tons in 30,372 hectares. In 2017, Brazil exported about 39,700 kg year -1 , generating USD 40.35 million revenue (BRAZILIAN FRUIT YEARBOOK, 2018).
The papaya cv. Formosa absorbs large amounts of nutrients continuously, especially in the first year (FONTES et al., 2010). To obtain the maximum crop yield and fruit quality required by the market there is a need to supply correct amounts of fertilizers (SANTOS et al., 2014).
Nitrogen is the second most required nutrient by the papaya plant and is responsible for vegetative growth (FONTES et al., 2010). Its absorption is continuous and increasing during plant cycle. In an experiment with nitrogen doses of 210, 428.4 and 642 kg ha -1 year -1 and constant doses of 85.7 kg ha -1 of P 2 O 5 and 428.4 kg ha -1 of K 2 O, Marinho et al. (2001) observed statistical differences in yield and number of fruits per plant. Silva Junior et al. (2016a, b) observed statistical differences in yield of papaya 'Caliman 01' as a function of different doses and sources of nitrogen, as well as for the interaction.
Phosphorus is required in smaller quantities by papaya as compared to N and K, but presents a great importance in the early stage of root development (OLIVEIRA et al., 2004). Evaluating combinations of N, P 2 O 5 and K 2 O for papaya 'Improved Sunrise Solo Line 72/12', Oliveira and Caldas (2004) and Oliveira et al. (2007) observed statistical differences in yield, and fruit quality. In Indonesia, Nasution, Noflindawati and Budiyanti (2011) observed a positive correlation between doses of phosphorus and number of fruits per plant, and average fruit weight in five papaya varieties.
Potassium is the most required nutrient by papaya and it is absorbed at a continuous and increasing rate along the plant cycle, with particular importance during the flowering and fruit set stage (OLIVEIRA et al., 2004). Testing different doses of K 2 O in papaya, Nascimento et al. (2009) observed an increase of 36.45% in the number of fruits per plant between the minimum and the maximum rate tested. Viana et al. (2008) observed quadratic increases with maximum number of fruits per plant with the dose of 157 kg KNO 3 ha -1 month -1 .
In a study carried out in five locations in India, Kumar et al. (2010) tested the doses 0; 150; 300 and 450 g K 2 O plant -1 year -1 , with fixed doses of N and P 2 O 5. The N-P 2 O 5 -K 2 O, combination of 300-300-300 kg ha -1 , was recommended to obtain highest yield, number of fruits per plant and fruit weight.
Due to the economic importance of papaya production, its increasing planted area and lack of research on papaya fertilization in the Chapada do Apodi region, this study tested the hypothesis that increasing doses of NPK increase yield of papaya 'Caliman 01', and there is a combination of NPK doses that provides the best economic return for papaya growers. The objective of this work was to study the effects of fertilization with different doses of nitrogen, phosphorus and potassium on yield components of papaya hybrid 'Caliman01', in order to determine the doses with maximum economic return and improve the sustainability of the crop fertilization.
Seedlings of papaya hybrid 'Caliman01' were transplanted to the field 30 days after germination, in the spacing 4.0 x 2.0 m, planting three plants per pit. The roughing was done at 90 days after transplanting (DAT), leaving one hermaphrodite plant per pit.
Treatments consisted of sixteen combinations of doses of N, P 2 O 5 and K 2 O. Five nitrogen doses (94, 590, 837, 1088 and 1575 kg N ha -1 ), five phosphorus doses (10, 72, 96, 133 and 195 kg P 2 O 5 ha -1 ) and five potassium doses (75, 527, 752, 978 and 1429 kg K 2 O ha -1 ), were combined according to the experimental matrix Pan Puebla II and distributed in a randomized block design, with five repetitions. The plots consisted of six plants and the four central plants were evaluated.
The fertilizers urea, monoammonium phosphate (MAP) and potassium chloride (KCl) were used as NPK sources, respectively. Urea and KCl doses were split in 30 applications, applied every two weeks, with the following distribution along the crop cycle: 83% of the urea and 30% of KCl doses were applied in the vegetative stage (15-120 DAT), 17% of the urea and 70% of KCl doses were applied in the flowering and fruit set stage (120-300 DAT). The MAP doses were split into two applications, 53% of the MAP dosage was applied at 75 DAT and the remainder at 150 DAT. The N added in the MAP applications was discounted from the applied urea doses.
Magnesium sulfate was applied as a source of sulfur and magnesium at dosage of 1.5 kg ha -1 , once a week, by Evaluation of NPK doses on the production of papaya 'Caliman 01' fertigation. Micronutrients were foliar applied using the commercial product Supra® with the following chemical composition, in g L -1 : 130 P 2 O 5 , 78 K 2 O, 26 Ca, 14.3 Zn, 6.5 B, 2.6 de Cu, 1.9 Fe, 1.3 Mo and 78 of total carbon, at a dosage of 0.8 L h -1 , once a month.
Irrigation was performed daily, 4 hours per day, using a drip irrigation system. Emitters with flow rate of 4 L h -1 were spaced every 0.50 m. During the vegetative phase it was used one drip line per row and in the reproductive phase two drip lines per row. The weed control was carried out using herbicides Glyphosate © and Gramoxone © . Preventively, were applied Oberon © , Abamec © and Ortos © to control mites and Calipso © and Decis © for insect control.
Harvest began at 190 DAT and was performed once a week, for eight months. Fruits were harvested when they presented two or three noticeable yellow stripes at their the base. At harvest the fruits were counted and weighed, obtaining this way, the number of fruits per plant, average fruit weight, production (kg plant -1 ) and yield (t ha -1 ).
The cost of each combination of NPK was determined taking as a basis the average price (in USD) per kilogram of N, P 2 O 5 and K 2 O are 0.51, 0.55 e 0.66, respectively. Revenue (benefit) from fruit sales was calculated considering the average price per kilogram (R$ 0.16). The most economical combination of NPK doses was determined by the cost/benefit ratio.
The data were submitted to analysis of variance to evaluate the effect of different combinations of NPK doses and the means were compared by the Tukey test at 5% probability. The effect of doses of N, P 2 O 5 and K 2 O was assessed by multiple regression analysis, using the statistical software SAEG 9.1 (UNIVERSIDADE FEDERAL DE VIÇOSA, 2007).

RESULTS AND DISCUSSION
The number of fruits per plant, average fruit weight, production and yield of papaya 'Caliman 01' were significantly affected by combinations of NPK doses ( Table 1). The largest number of fruit per plant was obtained with the combination of NPK doses 1088-72-527 kg ha -1 (combination 5), differing significantly from combinations 1, 7, 11, 15 and 16. The highest fruit weight was obtained with the combination of NPK doses of 590-72-978 kg ha -1 (combination 2), which was not significantly different from combinations of 3, 4, 6, 9, 11, 12 and 15. The highest fruit production and yield were 37.21 kg plant -1 and 46.51 t ha -1 , respectively, and were obtained using combination 5 (1088-72-527 kg ha -1 ), which did not differ significantly from combinations 8, 9, 12, 13 and 14.
Silva Júnior et al. (2016a) obtained a fruit production of 8.08 kg plant -1 and yield of 13.5 t ha -1 , when they applied 525 g of polymerized N plant -1 . Using urea as the source of N, they obtained a fruit production of 6.42 kg plant -1 and a yield of 10.7 t ha -1 for the maximum N dose (500.9 g plant -1 ). Both yields are smaller than those obtained by Brito Neto et al. For papaya variety 'Sunrise Solo', Oliveira and Caldas (2004) and Oliveira et al. (2007) obtained 102.4 fruits per plant after 12 months of harvest, using a combination of NPK 560-280-560 kg ha -1 . Marinho et al. (2001), working with the cultivar 'Improved Sunrise Solo Line 72/12' obtained 45.4 fruits per plant, using the combination of NPK 428.4-85.7-428.4 kg ha -1 .
Average fruit weight varied from 1.40 to 1.66 kg (Table 1) which was higher than those observed by Marinho et al. (2002) for cultivars of the 'Taiwan' group, 'Tainung 01/781' and 'Tainung 02/785', with average fruit weight of 1.35 and 1.11 kg, respectively, while for cultivar 'Know You 01/784 ', the average fruit weight was 2.01 kg, therefore, higher than those obtained in this work.
Production and fruit yield obtained in this study (Table 1) were lower than those obtained by Marinho et al. (2002), with cultivars 'Tainung 01/781'; 'You Know 01/784' and 'Tainung 02/785' (36.8 kg plant -1 and 45.8 t ha -1 , 36.1 kg plant -1 and 44.4 t ha -1 ; 24.5 kg plant -1 and 43.7 t ha -1 , respectively). That difference in production and yield may be attributed to plant density and harvest period, since in this experiment we used 1,250 plants ha -1 and the harvest season lasted eight months. Marinho et al. (2002) used 1.785 plants ha -1 , which were harvested for nine months.
The number of fruits per plant increased linearly as N doses increased (Figure 1a), while P and K reduced according to quadratic and linear trends, respectively (Figures 1b and 1c). Marinho et al. (2001) also observed a linear increase in the number of fruit with increases in nitrogen levels in papaya 'Sunrise Solo Line 72/12', while Oliveira and Caldas (2004) observed quadratic  (2016 a,b) reported a quadratic response in the production per plant and yield when N doses increased. Maximum yield values of 14,30 and 8.70 t ha -1 , were obtained with the doses of 498 and 460 g per plant for coated and conventional urea, respectively. The yield was 39.2% higher when the polymerized urea was used over conventional urea application . Brito Neto et al. (2011) reported that the production of fruits per plant presented an increasing linear behavior with increasing N doses, with the highest production of 7.8 kg plant -1 obtained with the dose 400 g plant -1 . The average fruit weight increased in a quadratic manner as a result of increasing of N doses, with a maximum value of 387 g obtained with the dose of 288.9 g plant -1 .
Increasing N levels did not significantly affect average fruit weight of papaya 'Caliman 01'. Marinho et al. (2001) also observed no effect of N rates on average fruit weight of cultivar Sunrise Solo Line 72/12. Doses of K showed a positive linear effect on average fruit weight (Figure 2), with an estimated increase of 29.3%. N doses linearly increased production of fruits per plant, providing estimated increase of 1.15 kg of fruits per plant per 100 kg N ha -1 (Figure 3a) . Brito Neto et al. (2009) also observed positive linear behavior of N rates in the production of papaya 'Sunrise Solo' (increase of 0.96 kg of fruits per plant per 100 kg N ha -1 ). However, Figure 3 -Fruits production of the papaya 'Caliman 01' in function of N rates combined with 72 kg ha -1 P 2 O 5 plus 527 kg ha -1 K 2 O (a); 01' in function of P 2 O 5 rates combined with 1088 kg ha -1 N plus 527 kg ha -1 K 2 O (b) and in function of K 2 O rates combined with 1088 kg ha -1 N plus 72 kg ha -1 P 2 O 5 (c) increasing P and K doses reduced fruit production of papaya 'Caliman 01' by 80.1% and 83.3%, between the highest and lowest doses of these nutrients, respectively (Figures 3b and 3c). Anjos et al. (2015) observed positive linear behavior of K rates in the production of papaya 'Tainung 01' with yield varying from 100 to 142 kg of fruits per plant. Allam, Taylor and Dicks (2000) evaluated the fertilization with NPK in papaya 'Solo' and did not detect effects of N, P and K on fruit quality. Fruit weight presented significant quadratic responses for N and P    applications, but there was a significant negative NK interaction, with higher levels of K, resulting in reduced fruit weight.
The combinations of NPK doses 12 and 14 showed the best benefit/cost ratios for production of papaya 'Caliman 01' (Table 3). There was an increase of the benefit/cost ratio for combinations 12 and 14 compared to combination 5, which means a financial return rate of 113% and 212%, respectively, considering only the economic aspect of the papaya fertilization. That return allows to infer that the combination of NPK doses 14 is the best option for the production of papaya 'Caliman 01' at the edaphic and climatic conditions of the site. Marinho et al. (2008) studied the effects of five irrigation depths and four K doses on yield and fruit quality of papaya cv. Golden ('Solo' group). During eleven months of harvest, the average yield was 79.4 t ha -1 and there were no significant differences among the treatments. However, in absolute values, the highest yield (96.4 t ha -1 ) was obtained with the combination of an accumulated irrigation depth of 1,525 mm and fertilization with 42 g K 2 O per plant per month. Silva et al. (2001) obtained a maximum yield of 30.9 t ha -1 for the papaya cv. Sunrise (six months of harvest) when they applied an irrigation depth of 2,731 mm. Oliveira and Caldas (2004) obtained, in twelve months of harvest, a maximum yield of 99.53 t ha -1 for papaya cv. Sunrise Solo, with fertilization doses of 272; 136 and 272 g plant -1 of N, P 2 O 5 and K 2 O, respectively.
Evaluation of NPK doses on the production of papaya 'Caliman 01' CONCLUSIONS 1. Under the conditions of the study, the increase of the nitrogen doses increased the yield of the papaya' Caliman 01', while the increase of the phosphorus and potassium doses reduced fruit yield; 2. The combination of 590-72-75 kg ha -1 of N, P 2 O 5 and K 2 O provided the best economic results for papaya production.