Agronomic and physiological responses of seed-potato in different organic substrates

Potato cultivation is very important, especially in organic systems. However, high cost and low availability of seed-potatoes are limiting factors. This study aimed to formulate and select an organic substrate to promote vegetative and reproductive development for seed-potato production. Four experiments were carried out in a greenhouse, in a completely randomized design with five replicates, with the cultivars (cv.) Aracy, Ágata and Aracy Ruiva, evaluating survival, leaf growth rate, gas exchange, agronomic variables, and macronutrients. Sprouts were used as propagation units. Experiment I was carried out to pre-select the best organic substrates, using cv. Aracy in 16 different substrates (S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, S11, S12, S13, S14, S15, and S16), with survival rates ranging from 80 to 100%. Experiments II, III and IV were carried out with 8 substrates; the second experiment was conducted with the cv. Aracy, the third experiment was conducted with the cv. Ágata and the forth experiment was conducted with the cv. Aracy Ruiva, and compared with commercial substrate (Mecplant®). The survival rates in the experiments were similar or higher than the commercial substrate. The substrates that promoted the highest leaf growth rate were S8 (experiments I and II), S11 (experiment III), and S9 (experiment IV). Substrates S8, S15, S1 and commercial promoted the highest instantaneous efficiency of carboxylation in plants of Aracy. The Aracy Ruiva grown in substrates S15, S8, S2 and commercial had higher internal concentration of CO ₂ ; and those grown in S3 had higher instantaneous efficiency of water use. The eight substrates selected provided similar mass, diameter and length of tubers produced by all cultivars, when compared to the commercial substrate. Significance was observed only for Ágata, regarding the number of tubers. Among the organic substrates evaluated, substrate S11 is indicated for the production of seed-potatoes, as it promotes the highest survival among the evaluated substrates, high leaf area development, being the highest to the cv. Ágata, promoted tuberization, increasing the tuber number produced by the plants and the tuber mass, and length and transversal diameter tuber of the evaluated cultivars and the substrate is formulated with washed coconut powder; sifted poultry litter; humus, limestone and sand, products easily to find by growers, with low cost and allowed to use in organic agriculture.