Production and composition of Chinese cabbage under plastic rowcovers in southern Spain

The effects of plastic rowcovers on the growth and quality of Chinese cabba ge (Brassica pekinensis (Lour) Rupr. 'Nagaoka 50') were investigated in Gra nada, southern Spain (latitude: 37 degrees 10' 21" N; longitude: 3 degrees 38' 10"E; elevation: 600 m), for three years. Polyethylene (T-1) and polypr opylene (T-2) covers increased air temperature by 7K and 5K, and soil tempe rature (5- and 15 cm depth) by 3-4K and 2K, respectively, compared with plo ts in the open (T-0). In contrast, radiation levels in T-1 and T-2 were red uced by 12% to 16%, respectively. Thus, total shoot fresh weight was 111% ( T-1) and 108% (T-2) greater under rowcovers, and the commercial head weight s were 105% (T-1) and 96% (T-2) greater, and dry weights 21% (T-1) and 13% (T-2) greater than T-0. These differences in plant production were reflecte d in higher yields under plastic, and a higher proportion of marketable hea ds (23% in open air compared with 68% and 65% under T-1 and T-2, respective ly). The concentration of soluble sugars and pigments were also lower in th e shoot under rowcovers than in plants in the open air. There were only sma ll differences between the two plastic covers. Slightly warmer conditions a nd less shade under polyethylene compared with polypropylene provided great er plant production, yields and sugar concentrations, but lower pigment con centrations. Growing Chinese cabbage plants under plastic rowcovers in sout hern Spain increased production without significantly affecting composition .