Correlations between soil and cladode nutrient concentrations and fruit yield and quality in cactus pears, Opuntia ficus indica in a traditional farm setting in Argentina

Abstract

Soil and cladode relations were examined between yield and fruit quality in an 8-year-old planting of Opuntia ficus indica in a traditional farm setting in Santiago del Estero, Argentina. The plantation had a relatively high mean yield and fruit soluble solids concentration of 19.5 Mg ha −1 and 15.0%. Five fertilizer treatments: (1) control, (2) 100 kg N ha −1, (3) 100 kg ha −1 N and 50 kg ha −1 P, (4) 100 kg ha −1 N+50 kg ha −1 P+100 kg ha −1 K and (5) 100 kg ha −1 N+50 kg ha −1 P+100 kg ha −1 K+50 kg ha −1 Mg were applied to the soil of 10 plants per treatment (total of 50 plants but 4 died during the experiment). There were no significant influences of these soil applications on fruit yield or quality. Additionally correlations were examined between yield, quality (Brix, fruit firmness, % pulp) and 11 cladode nutrients and 7 soil nutrients for the 46 individual plants. The only significant positive correlations with yield were for exchangeable soil Ca concentrations and the ratio of cladode Ca/Mn. Yield was very highly significantly negatively correlated with cladode Mn and significantly negatively correlated with cladode Zn concentration. While this was surprising, given the mean Ca/N ratio of 3.95 in Opuntia vs. approximately 0.50 in field and fruit crops, the importance of Ca to Opuntia mineral nutrition seems reasonable. The significant positive Ca/Mn correlation suggests a beneficial role of Ca in mediating a slight toxic Mn effect. Fruit firmness was highly correlated with cladode K concentrations, which is reasonable given that K is the most abundant nutrient in cactus fruits. Although this local variety has excellent firmness, it will be important to examine the role of K in other very high yielding varieties which have low consumer acceptance due to low pulp integrity and firmness. While fruit yield was not correlated with cladode protein, it is nevertheless important to maintain adequate protein for regulatory processes and photosynthesis. The cladode N was highly significantly correlated with cladode Ca, Cu, K and Mn and Zn in that order. Since the N fertilization treatment did not stimulate cladode micronutrient concentrations, the high correlations between cladode N and Cu, Mn and Zn may indicate micronutrient limitations. Given the higher Ca/N and K/N ratios in Opuntia than other crops, and the highly significant correlations we observed between yield and exchangeable soil Ca, it appears that the importance of the basic mineral nutrients Ca and K have been overlooked, and that future Opuntia fruit yield/quality trials should give priority to these nutrients.