Acúmulo de massa seca e nitrogênio durante o ciclo de crescimento e desenvolvimento da batata

Abstract

The goal of this work was to determine the effect of N supply in growth, development and yield of potato plants and the implications to N fertilization in this crop. The experiment was conducted in a greenhouse of the Fitotecnia Department of UFSM, from September 2 to December 12, 2003. Potato tubers of the cv. Asterix were planted in 5 dm3 polyethylene bags filled with an organic substrate. Plant density was 4.4 plants m-2. Plants were fertigated with a complete nutrient solution. Treatments consisted of five nutrient solutions differing in N concentration, (mmol L-1): 5.0 (T1); 8.3 (T2); 11.3 (T3); 14.3 (T4) and 16.3 (T5). Standard concentrations were used for all other nutrients, (mmol L-1) 8.3 of K+; 3,5 of Ca++; 1,4 of Mg++; 1,4 of SO4 -; 1,2 of H2PO4 micronutrients were also added. Five plants of each treatment were harvested at seven-day intervals, from 43 to 99 days after planting, to determine dry mass, number of tubers and leaf area index (LAI). The N concentration of plant tissues was determined by Kjeldahl s method. Tuber yield was determined at the and of the experiment. Shoot and tuber dry mass increased with N levels, reaching maximum values at T4 and decreasing at T5. Vegetative dry mass was similar in T1 and T2, reaching the maximum value in T4. Maximum LAI increased by a factor of 0.5 from T1 to T4. Plant cycle increased from 78 days in T1 to 99 days in T4/T5. Tuber number also increased from T1 to T4. Based upon the results, nutrient solutions with N concentrations between 14.3 and 16.3 mmolN L-1 are needed for tuber number; and about 12 mmolN L-1 for maximum tuber size. These N concentrations can be used in open hidroponical systems with organic substrates. Nitrogen dilution was observed in all organs during plant growth and development. The experimental data fitted well in the model %N= aMS-b described in the literature. The critical nitrogen curve of the whole plant was adjusted with values of 3.6 and 0.367 for a and b, respectively. This curve can be used as a referential point to infer results from foliar analysis and to estimate N uptake during growth and development of potato plants.