The objective of this study was to evaluate the performance of onion cultivars as a function of the spacing between plants. The experimental design was a complete randomized block in a 3 x 4 factorial scheme, with four replicates. The treatments were composed of the combination between three onion cultivars (Vale Ouro IPA 11, Serena and Rio das Antas) and four plant spacings (3, 6, 8 and 10 cm). The evaluated characteristics were total, marketable and unmarketable yield of bulbs, percentages of bulbs in classes 1, 2, 3 and 4, bulb mean weight, bulb dry weight. In onion cultivation, the cultivars Rio das Antas and Serena are the most indicated, with the highest marketable yields at 6 and 3 cm spacings between plants, respectively. The cultivar Vale Ouro IPA 11 presented higher marketable yield for the spacing of 5 cm between plants.

Nitrogen exerts a marked influence on the yield and quality of the onion. The present work was developed from June to October 2016, aiming to evaluate the yield and quality of two cultivars of onion under a system densified as a function of nitrogen doses in Mossoró, RN, Brazil. A randomized block design was used in a 2 x 7 factorial scheme, with four repetitions, corresponding to two cultivars (IPA 11 and Rio das Antas) and seven nitrogen doses (0, 45, 90, 135, 180, 225 and 270 kg ha-1 of N), provided by fertigation, with four repetitions. The dose of 92 kg ha-1 of N provides the highest total and marketable yields of bulbs. Nitrogen fertilization increases the concentrations of N, chlorophyll a, b and total in the leaves of the onion, as well as the percentage of bulbs of classes 3 and 4 and the pungency, reducing the percentage of bulbs of class 2 and non-commercial. The doses of 108 and 82 kg ha-1 of N provide the highest rates of return for ‘IPA 11’ (R$ 2.07) and ‘Rio das Antas’ (R$ 2.41), respectively.

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.

Although watermelon is one of the major vegetable-fruit crop, management fertilization still lacks information for increased productivity, quality and profitability, and to lower environmental impact. An experiment was conducted in Mossoró, Brasilian city of Rio Grande do Norte, from August to October 2012, to evaluate the effects of doses of phosphorus (P) (0, 45, 90, 135, 180 and 225 kg ha-1 P 2 O 5) in productivity, quality and profitability of two cultivars of watermelon cultivation (Top Gun and Olympia), in a randomized blocks in a factorial 6 × 2, with four replications. Larger number of commercial fruits (1.70 per plant) and commercial yield (74.39 t ha-1) were obtained with 54.8 and 49.4 kg ha-1 P 2 O 5 , respectively. Attributes of quality of watermelon fruit were not influenced by P. Dose between cultivars differences were found, and 'Olympia' had higher fruit mass and skin thickness than the 'Top Gun'. However, the soluble solids content of the 'Top Gun' was 4.9% higher than the Olympia. The maximum economic return was achieved with a dose of 49.37 kg ha-1 of P 2 O 5 .

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.

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 P 2 O 5 ). 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 P 2 O 5 , 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.