Mineral nutrition enhances yield and affects fruit quality of 'Cristalina' cactus pear.

摘要

Cactus pear (Opuntia spp.) responds positively to supplemental organic and mineral nutrition. There are several recommended rates and sources of mineral nutrition for this crop. However, there is no information on ways to produce optimal fruit yield in cactus pear. The objective of this study was to test a nitrogen-phosphorus-potassium (NPK) fertilization matrix over three consecutive growing seasons and to determine its effect on yield and fruit quality of 'Cristalina' cactus pear. In the second and third growing seasons, mineral nutrition significantly increased fruit yield. Average yields were 9.6, 12.1, and 21.6 t ha-1 for the 2004, 2005, and 2006 growing seasons, respectively. Supplemental nutrition at a rate of 90N-30P-30K increased fruit yield 13.4- and 5.2-fold in the 2005 and 2006 growing seasons, respectively, over unfertilized control plants. Application of K alone had no effect on fruit yield. Therefore, the maximum biological response of fruit yield was estimated at 30.3 t ha-1 with 90 kg ha-1 N and 30 kg ha-1 P. Although fruit number increased, fruit size, as mean fruit weight, was similar among treatments. Fruit quality, determined as peel firmness, peel to pulp ratio, and total soluble solids concentration, exhibited inconsistent responses to supplemental mineral nutrition. Fruit dry matter was reduced as N and P application rates increased. Cladode macro- and micronutrients were found in sufficient concentrations, except for Mn. Even when Mn was at high concentrations, no toxic effects were observed in cactus pear plants. Spearman rank correlation between some fruit quality attributes and nutrient concentrations found a significant positive association between fruit firmness and cladode K concentration, but negatively association between TSSC and cladode N and K concentrations. Nutrient use efficiency decreased as N and P application rates increased. After plant and soil mineral analysis, the 90 kg ha-1 N and 30 kg ha-1 P could be applied to production sites by cactus pear growers. The lack of fruit yield response from cactus pear to K fertilization should be studied further because cactus pear extracts ~54 kg K year-1. Over the long term, this constitutes an important drain on the ecosystem if no K is added back.