Densidade populacional do feijão-caupi sob níveis de irrigação

Abstract

The cowpea is a crop traditionally produced in the North and Northeast regions. In the state of Piauí, its low average income still persists today, despite the culture was well adapted to soil and climatic conditions of the region and there are improved cultivars available on the market. Thus, studies that describe best practices in crop management with the proper combination of plant density and irrigation levels, are important as they are able to present alternatives that enable increased efficiency of water use by the crop and reduce costs with agricultural inputs. The aim of this study was to evaluate the possible interaction of water levels and plant density on cowpea growth parameters, gas exchange, yield components, grain yield, efficiency of water use and distribution of soil moisture. The experiment was conducted during the period July to September 2012 in the experimental field of Embrapa Meio-Norte, located in the city of Teresina, Piauí. Treatments consisted of five irrigation (L5 -150%, L4 -120%, L3 - 90%, L2 - 60% and L1 - 30 % of ETo) and four densities (D1 – 150,000, D2 - 200,000, D3 -250,000, D4 – 300,000 plants ha-1). There was a significant interaction between irrigation levels and population densities for yield components, number of pods per plant, weight of pods, pod yield, pod length, pod weight of hundred grains, grain yield and water use efficiency. Grain yield showed the maximum value of 1668.86 kg ha- 1 with a water depth of 390.88 mm associated with the density of 241,000 plants ha- 1. Obtained the maximum efficiency of use of water, 4.78 kg ha-1 mm-1 with the blade of 342.97 mm and density of 233,000 plants ha-1. As regards the distribution of soil moisture under the higher irrigation regimes and different seeding rates, water consumption was different cowpea depending on the density of roots. The pattern of water extraction from the soil by roots of cowpea was directly proportional to the seeding densities evaluated. There was wide variation in water extraction in different densities of cowpea when subjected to minor irrigation. Under a water depth of L5 - 150% ETo and plant density of 241,000 plants ha- 1, the cowpea responsive in terms of production, maintaining the available water capacity in the soil, in the approximate range of 80% (in the layer of 0.10 m) to 60% (in the layer of 0.30 m). A significant interaction between irrigation levels and population densities for leaf area of cowpea, indicates that there is a reduction in growth with decreases in water levels and plant density parameter. The highest values occur with irrigation depth of 367.86 mm and density of 188,000 plants ha- 1. Separately, the continuous application of water increased the photosynthetic rate, stomatal conductance and transpiration with reduced values in the smaller irrigation 201.73 mm and 260.39 mm .