Effect of irrigation with injection of air in soil moisture, nitrate availability, electrical conductivity and lettuce productivity grown in plastic greenhouse.

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 MitraICAM, 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. Key-words: Lactuca sativa L., oxygation, root length density, subsurface drip irrigation