Efeito da rega com injecção de ar na humidade do solo, dis­ponibilidade de azoto nítrico, condutividade eléctrica e pro­dutividade da alface cultivada em estufa plástica

The objective of the present study was to evaluate the effect of the air injection through subsurface drip irrigation (oxyga­tion) in soil moisture, availability of nitro­gen oxide, and electrical conductivity, plant growth and yield of lettuce, variety "Men­tion", cultivated in plastic greenhouse. The experiment was carried out at the Mitra-ICAM, an Experimental Station of the Uni­versity of Evora -Portugal. The experiment was arranged in a randomized block design with four replications and the treatments were: irrigation with (CAR) and without (SAR) air injection. The air was introduced into irrigation water through a jet "Mazzei". The soil moisture in the surface layer (0­0.05 m) was similar for the two treatments, reaching values around zero. Concerning NO3-concentration in 0.10-0.20 m soil layer at 35 and 47 days after planting was higher in the treatment CAR. At 47 days after plant­ing, the average levels of NO3-were 95.33 and 67.94 ppm respectively in treatments CAR and SAR. Air injection increased root length density at 0-0.10m depth. The com­mercial yield was not affected by air injec­tion. The lack of response by the crop to the increase of the soil nitrate concentration and root length density could be related with the short cycle of the crop and/or with high con­tents of nitrogen present in the soil, or result of the dripline setting depth.