Beetroot (Beta vulgaris L.) is a tuberous vegetable that is under experimentation in the vegetable production system in Rio Grande do Norte state (Brazil). It is quite demanding, in nutritional terms. One of the alternatives to meet this need is green manuring using spontaneous species of the Caatinga biome. The aim of the present work was to optimize the agro-biological performance and economic profitability of the beetroot 'Early Wonder', fertilized with different doses of hairy woodrose (Merremia aegyptia (L.) Urb.) in this semi-arid environment. Hairy woodrose is a spontaneous species of the Caatinga biome that is widely distributed, being found in forests, fences, forest clearings and fields, growing in soils of different textures, producing biomass with a high content of macronutrients. This material was collected from spontaneous vegetation, native to the region, and used as green manure.The experimental design was a randomized complete block, with four treatments and five replicates. The treatments consisted of four amounts of hairy woodrose biomass incorporated into the soil (10, 25, 40 and 55 t ha-1 of dry matter). The following agronomic characteristics were evaluated in each beetroot treatment: plant height, fresh mass of shoots, number of leaves per plant, dry mass of shoots and dry mass of roots, total and commercial root productivity, and root productivity classified into scrap and extra roots, extra A roots, extra AA and great roots. Apart from these characteristics, the following economic indicators were also determined for each treatment: gross income, net income, rate of return and profit margin. The maximum agro-biological efficiency of beet root productivity (22.68 t ha-1) was obtained from 44.92 t ha-1 of hairy woodrose biomass added to the soil. The maximum economic efficiency of the yield of beet roots was achieved as a net income of AU$2,491.00 (R$6,406.36) ha-1, provided by the production of 22.04 t ha-1 of commercial roots, using 37.03 t ha-1 of hairy woodrose biomass incorporated into the soil. The use of hairy woodrose as green manure presents agro-economic feasibility in beet cultivation in this semi-arid environment.
