Plants often express deficiencies with visible abnormalities; however, it is necessary to obtain reliable information to make the proper diagnosis about the missing nutrients. Until now, research with this approach has not been carried out for crops such as feijoa (or pineapple guava). For this reason, the present investigation identified and described the symptoms produced in young feijoa plants due to poor fertilization of N, P, and K and its effect on some components of plant growth and development. To achieve this, different treatments were established: complete fertilization (control); complete fertilization -N; complete fertilization -P; complete fertilization -K; and one treatment with no element (negative control, H2O). We determined the symptoms associated with each deficiency by means of a photographic record and the description of the symptoms. Among these nutrients, N deficiency yielded the highest plant detriment, due to lower growth and a global pale green coloration, while -P plants showed foliar malformations and necrosis, -K plants exhibited the brown margin in old leaves, then turning necrotic, while young leaves showed a lack of turgor. Also, lack of N seriously affected apical growth, number of basal and apical shoots, and chlorophyll foliar content, while the -P and -K developed lower growth rate in the shoot than in the control. Such symptoms were registered after two months of treatment. This study indicated that the greatest affectation of the feijoa was due to a lack of nitrogen; and also P and K deficiencies showed symptoms and growth characteristics that were altered in the development of the plants.

Nutrient deficiency symptoms are widely used to determine the nutrient demands of a crop and to clarify nutritional disorders, especially when they are nutrient specific. Until now, a calcium (Ca), magnesium (Mg) and boron (B) deficiency experiment has not been carried out on feijoa, and diagnostic symptoms have not been described. For this reason, 9-months-old ‘Quimba’ feijoa plants were studied using the missing nutrient method. A modified Hoagland and Arnon solution was applied for each treatment, leaving out one element in each treatment. The treatments were: (1) complete fertilization (control); (2) complete fertilization -Ca; (3) complete fertilization -Mg; (4) complete fertilization -B; and (5) without fertilization (negative control). Deficiency symptoms in the plants were described, and photographic records were made. The Ca deficiency was noted early in the shoot tips and later in fully-expanded, young leaves. The Mg-deficiency was observed in older and fully-expanded leaves, mainly as interveinal chlorosis, while the B deficiency generated a variety of symptoms, interveinal and total chlorosis in fully and not fully-expanded leaves and a mosaic of symptoms in adult leaves. For the growth components, the Mg deficiency reduced the number of apical shoots, while the Ca- and Mg-deficiencies reduced the seedling growth rate significantly. For future experiments, the authors suggest an experiment period longer than 102 d to achieve more conclusive results.