Nutrição mineral nas fases de semeadura e de individualização de “seedlings” do melhoramento genético de cana-de-açúcar

Abstract

The concern and interest in ensuring the adequate nutritional supply for plant cane and ratoon cane, and even for propagation seedlings, has been quite evident. However, there is little information on the supply of nutrients in the different stages of the sugarcane breeding, especially during sowing and individualization of seedlings and the initial acclimatization of seedlings in the nursery and field conditions of phase T1. The understanding of these effects can guarantee the full development of the seedlings, in order to avoid masking and the elimination of some genotype of high productive potential. The general objective of this work was to study the influence of nutrient supply by nutrient solution on the development of seedlings in the initial phase of the selection process of sugarcane genotypes adopted by PMGCA-UFSCar. The specific objectives were: (a) to evaluate the effects of frequency of application and concentration of nutrient solution on biometric parameters of development of sugarcane seedlings; and (b) obtain subsidies to suggest seedlings fertigation as a routine practice. Sugarcane seeds originating from biparental crossings RB925211 x RB855463, SP803280 x RB855536 and RB935744 x RB72454 were used. The seedlings were individualized in containers with vermiculite to compose the treatments, arranged according to a completely randomized design, under controlled greenhouse conditions for three months, with a 3x3x3 factorial scheme, using 12 replicates per treatment. The frequency of application (1, 2 and 3 times a week) and the concentration of the nutrient solution (calculated - C, half C / 2 and double 2C) were tested on seedlings grown in vermiculite, with the substrate Multiplant®, used in routine of the PMGCA-UFSCar, as a reference. The low rate of sugarcane seeds germination and the early death of seedlings could not be attributed to the temperature fluctuations registered in the greenhouse. The germination of sugarcane seeds was more homogeneous under germination chamber conditions, with a photoperiod of 12 h and a temperature of 30 °C. In the first month after harvesting, seedlings kept in the Multiplant® substrate showed the highest growth in height and mild copper (Cu) deficiency, with no visual symptoms. In the period of 30-60 days after growing, seedlings grown on the Multiplant® substrate showed nitrogen (N), sulfur (S), copper (Cu) and manganese (Mn) deficiency, showing visual symptoms only for S, characterized by chlorotic young leaves with reddish-purple edges. In this period, the application of nutrient solution three times a week, at a concentration equivalent to two times the calculated concentration, constituted the most appropriate treatment for the crosses studied. In the third month after harvesting, seedlings of the Multiplant® substrate continued to be deficient in N and S. The application of nutrient solution twice a week, at a concentration equivalent to two times the calculated concentration (2x2C), was the most appropriate treatment for the studied crosses, in the period of 60-90 days after the breeding. The application of a nutrient solution with a concentration equivalent to two times the calculated one, twice a week, represented the most appropriate treatment to be incorporated as a fertigation routine for seedlings from the crossings covered in this study.