Alterações na nutrição mineral do meloeiro em função da salinidade da água de irrigação.

Abstract

A field experiment was carried out at 'São João' farm, Mossoró-RN, during September 15 to November 28, 2000, to study the nutrition changes in melon irrigated with waters of different salinity leveis. The experiment combined three factors: irrigation water salinity leveis (SI = 1.1 dS.m"1; S2 = 2.5 dS.m"1 e S3 = 4.5 dS.m"1), two melon cultivars (Trusty e Honey Dew Orange Flesh) and two irrigation tums in two leveis (Fi = one-day interval turn and twice a day and F2 = two-days interval turn and once a day depending on the plant age). For nutrient and growth analyses, the plants collected at five times (22, 29, 36, 47 e 61 days after sowing (DAP)), from the four replications of each treatment, vvere combined to form a new experimental plot for each collection time. With this new arrangement, it was evaluated the effect of the three salinity leveis and the two cultivars according to a completely randomized 3 x 2 factorial scheme utilizing F] and F2 as replications. A multivariate analysis was performed considering each collection time as another factor. The sampled plants were divided into two portions, which were analyzed separately for dry matter yield and macronutrient contents. The accumulation of dry phytomass in the plant decreased with increasing irrigation water salinity levei. The initial plant growth was slow in the first 37 DAP, with dry plrytomass reaching a maximum at 61 DAP. Phytomass distribution in the treatments with salinity leveis (SI, S2 e S3) was 33.93,41.28 and 42.58% in the plant shoot and 66.07, 58.72 and 57.42% in the fruits, respectively; in the cultivars was 32.86 to 45.55% in the shoot portion and 54.45 to 67.14% in fruits, respectively. The total of nutrients (N, P, K and Mg) exported by the plant decreased with increasing water irrigation salinity levei. The macronutrient contents (N, P, K and Mg) in the dry phytomass decreased along the crop cycle, while Ca content increased at the end of the cycle. The sequence of magnitude of the average macronutrient contents in the phytomass was K > N > Ca > Mg > P, with the melon plant nutrient uptake behaving as well. On an average basis, of the total amounts of absorbed nutrients the fruits exported 57.13%, 67.06%, 69.94%, 18.31% and 41.03% of N, P, K Ca and Mg, respectively, with the nutrient accumulation sequence in fruits following the order K > N > P > Mg > Ca. Nutrient use efficiency regarding both cultivars and increasing salinity leveis was P > Mg > Ca > N > K.