ABSTRACT. The management of weeds in melon is hindered by the slow initial growth of the crop, favouring weed infestation and reducing production. During the years 2016 and 2017, weed interference periods were evaluated in two melon hybrids, yellow and frog skin, to determine the time of weed control in the crop. Four-parameter logistic regression was used to determine the critical weed control period (CPWC). The weed species with the highest occurrences in 2016 were Merremia aegyptia, Senna obtusifolia, and Urochloa plantaginea. In 2017, there was a predominance of M. aegyptia, indicating the possibility of successive cultivation, favouring the predominance of species with growth habits similar to melons. The increase in the period of living with weeds reduced the productivity and quality of melon fruits. Coexistence with weeds throughout the cycle reduced productivity by about 50%. The CPWC was 15 to 58 and 10 to 45 for frog skin and 12 to 52 and 4 to 50 days for yellow melon in 2016 and 2017, respectively, considering a productivity loss of 5%. These results underscore the importance of adopting strategies that allow melons to grow free from the presence of weeds, especially before they are fully established in the growing area.

ABSTRACT Phosphorus (P) is an important nutrient for obtaining high yields and has been the one that most often limits production. The objective of this study was to evaluate the agronomic performance of onion cultivars as a function of phosphate fertilization. The experiments were installed at the Rafael Fernandes Experimental Farm, of the Federal Rural University of the Semi-Arid Region, Mossoró-RN, Brazil, from July to October 2016 and from June to October 2017. The design used was randomized blocks, in a 2 x 6 factorial scheme, with four replicates. The treatments consisted of the combination of two onion cultivars (IPA11 and Rio das Antas) and six P doses (0, 60, 120, 180, 240 and 300 kg ha-1 P2O5). The economical doses of P, associated with the maximum marketable yields of onion were estimated at 212.45 and 207.65 kg ha-1 of P2O5, respectively for the cultivars IPA 11 and Rio das Antas. In general, the cultivar Rio das Antas was more productive than IPA 11, in the two growing periods.

RESUMO O aumento na densidade de plantas aliado à utilização de híbridos no cultivo da cebola tem proporcionado ganhos significativos na produtividade desta cultura, com impacto direto na quantidade de macronutrientes absorvidos. Objetivou-se avaliar a produtividade e qualidade de duas cultivares de cebola sob sistema adensado em função de doses de potássio fornecidas via fertirrigação em Mossoró/RN. Adotou-se o delineamento em blocos casualizados, em esquema fatorial 2 x 7, com quatro repetições. Os tratamentos constituíram-se de duas cultivares (IPA 11 e Rio das Antas) e sete doses de potássio (0, 70, 140, 210, 280, 350 e 420 kg ha-1 de K2O), fornecidas via fertirrigação. As doses de potássio que proporcionaram as máximas produtividades total e comercial de bulbos foram de 215 e 216 kg ha-1 de K2O, respectivamente. Os sólidos solúveis e o percentual de bulbos das classes 2, 3 e 4 não foram influenciados pela adubação potássica. Houve redução do percentual de bulbos não comerciais com o aumento das doses de potássio. A dose de máxima eficiência econômica foi de 210,6 kg ha-1 de K2O, responsável por uma produtividade comercial de 61,8 t ha-1.

ABSTRACT The increase in plant density, combined with the use of hybrids in onion cultivation, has provided significant gains in yield, with a direct impact on the amount of absorbed macronutrients. The present work aimed to evaluate the yield and quality of two onion cultivars under a densified system as a function of potassium doses supplied via fertirrigation. A randomized complete block design was used in a 2 x 7 factorial scheme with four replications. The treatments consisted of two cultivars (IPA 11 and Rio das Antas) and seven potassium doses (0, 70, 140, 210, 280, 350 and 420 kg ha-1 K2O), provided by fertigation. The potassium doses that provided maximum total and commercial yields were 215 and 216 kg ha-1 of K2O, respectively. The soluble solids and the percentage of bulbs of classes 2, 3 and 4 were not influenced by potassium fertilization. There was a reduction in the percentage of non-commercial bulbs with the increase of potassium doses. The dose with maximum economical efficiency was 210.6 kg ha-1 of K2O, responsible for a commercial yield of 61.8 t ha-1.

Resumen: El objetivo de este estudio fue evaluar el crecimiento y acumulación de macro y micronutrientes en la planta del melón híbrido Ibérico (Syngenta Seeds). El experimento fue realizado entre enero y abril de 2013 en la hacienda experimental «Rafael Ferdandes» de la Universidade Federal Rural do Semi-Árido, ubicada en Mossoro, Río Grande do Norte, Brasil. El diseño experimental utilizado fue el de bloques al azar con once tratamientos y cuatro repeticiones. Los tratamentos consistieron en colectas a los 0, 7, 14, 21, 28, 35, 42, 49, 56, 63 y 70 días después del transplante. El estudio cuantificó las acumulaciones de materia seca, nitrógeno (N), fósforo (P), potássio (K), cálcio (Ca), magnésio (Mg), zinc (Zn), hierro (Fe), manganeso (Mn) y cobre (Cu) en la parte vegetativa (hojas y tallos), frutas y planta entera. Al final del ciclo los frutos acumularon mayor cantidad de materia seca, correspondiendo al 73,7 % del total. El N, P, K, Fe, Mn, Zn y Cu se acumularon preferencialmente en los frutos, mientras el Ca y Mg lo hicieron en la parte vegetativa. La mayor acumulación de masa seca y nutrientes ocurrió entre 35 y 49 días después del trasplante, con la excepción de calcio, magnesio, cobre y zinc que extendieron su acumulación hasta el final del ciclo. El orden decreciente de acumulación de nutrientes para el melón híbrido ibérico fue: N> K> Ca> P> Mg> Fe> Zn> Mn> Cu.

Summary: The objective of this work was to evaluate the growth and accumulation of plant nutrients in Ibérico hybrid melon (Syngenta Seeds). The experiment was carried out at the «Rafael Ferdandes» experimental farm of the Universidade Federal Rural Semi-Arido in Mossoró, Rio Grande do Norte, Brazil, from January to April 2013. We used a randomized block design with eleven treatments and four replications. The treatments consisted of the sampling periods: 0, 7, 14, 21, 28, 35, 42, 49, 56, 63 and 70 days after transplanting. This study assessed dry matter, nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu), the vegetative part (leaves and stems), fruits, and whole plant. The fruits were the preferred drain of the plant, corresponding to 73.7 % of the dry matter accumulated. The N, P, K, Fe, Mn, Zn and Cu were accumulated preferentially in fruits, while Ca, and Mg accumulated in the vegetative part. The highest accumulation of dry mass and nutrients occurred from 35 to 49 days after transplanting, with the exception of calcium, magnesium, copper and zinc that extended their accumulation until the end of the cycle. The decreasing order of nutrient accumulation for the Ibérico hybrid melon was: N > K > Ca > P > Mg > Fe > Zn > Mn > Cu.