Necessidades hídricas, crescimento e desenvolvimento do abacaxizeiro nos tabuleiros de Santa Rita-PB.

Abstract

The Paraíba State is a traditional producer of pineapple crop, which fruits are outstanding by their quality and flavor due to its favourable soil and climatic conditions. The pineapple crop, with good water supply, change its water consumption as compared to the rain-fed crop. So that, for a better crop management and rational use of water it is necessary to know the water requirements of the crop. With this objective, an field experiment was conducted in the rural area of Santa Rita-PB during the period from March, 2001 to June, 2002, in an irrigated area of 0.80 ha grown with pineapple (Ananas comosus (L) Menu), cv. Pérola crop, planted in a spacement of 0,80 m between rows by 0.25 m between plants. Two micrometeorological towers were installed in the experimental area: one with sensors of net radiation and reflected solar radiation and another with sensors of global solar radiation, dry and wet bulbs temperatures and wind velocity at two levels: 0.2 m and 1.2 m above crop canopy. In the soil, under the leaves, a soil heat flux plate was installed at 0.02 m depth and an evapotranspirometer was connected to a drainage tank with 1.80 m x 2.40 m x 1.0 m and 0.80 m x 1.20 m x 1.20 m volumes, respectively. The analogical signals of the radiometers, psychrometers, anemometers and fluxmeters were collected by a data acquisition system (Data Logger CR 10X) and were used for the determination of the Bowen ratio energy balance. Throughout the field experiment, it was detected problem with the management and use of the evapotranspirometer, what made impossible the measurements of évapotranspiration by this technique. The reference évapotranspiration was determined by the FAO (Penman- Monteith) method. As crop morpho-physiological variables, the plant diameter and height and number of leaves were measured. Based on dry-matter and leaf area, relative and absolute growth rates, leaf area index and net assimilation rate were determined. Also, yield aspect and fruit quality were analyzed. The net radiation and reflected solar radiation were 63% and 14% of the global solar radiation while the latent heat flux (LE) was 80% of the net radiation. In terms of crop évapotranspiration (ETp), the phase I (crop growth) was divided into two sub-phases ( I I and 12) with ETp values of 4.2 mm.d"1 and 4.5 mm.d"1, respectively while, for the other phases, were obtained the following values of ETp: 4.4 for the phase JJ (flowering/flowers fall), 3.8 for phase m (fruit development) and 3.5 for phase IV (fruit harvest). For the whole crop cycle, the mean value of ETc was 4.1 mrn-d"1. The crop coefficient (Kc) was not constant throughout the crop cycle, so that the use of this index should be made with restrictions. However, for the first 140 days after planting ETp = 0.7 while for rest of the crop cycle a value of ETp = 0,9 may be used. The growth variables were compared to those described in the literature. The fruits considered as first class had weights above 1.7 Kg, corresponding to 60% of the total harvested fruits (57,000 Kg). The fruits considered as of second and third classes had weights between 1.3 Kg and 1.7 Kg (30% of the total fruits harvested) and bellow 1.3 Kg (10% of the total fruits production, which were considered to be used in the industries of juices and animal rations.