Integrated management of K -additives to improve the productivity of zucchini plants grown on a poor fertile sandy soil

Three eco-friendly approaches were investigated for their effects on improving K-uptake by zucchini plants; hence, increasing shoot growth and fruit productivity. These approaches were: (1) amending soil with biochar (0 and 5g kg-1), (2) spraying plants with Amphora extract (0 and 1g L-1) and (3) substituting inorganic-K fertilizers partially with organic ones. In this concern, five levels of compost (0, 1.5, 3, 4.5 and 6 g kg-1) were applied to a poor fertile sandy soil (98.5% sand) in complementation with inorganic NPK-fertilizers to bring their concentrations, even in the control treatment, to the recommended levels. This investigation was conducted under the greenhouse conditions during the summer season of 2020. Results obtained herein reveal that application of either of biochar or Amphora extract exhibited positive effects on soil available-K (20 and 6.5% respectively), K-concentrations in fruits and total K-uptake by the aboveground plant parts. Furthermore, these two amendments raised considerably the dry weights of both zucchini shoots and fruits. On the other hand, compost could partially substitute inorganic-K fertilizers when it was applied at a rate not exceeding 3g kg-1, recording significant improvements in all the investigated parameters. Nevertheless application of high compost doses reduced significantly fruit yield. Generally, there existed a highly significant linear relation between the total K-uptake by plants and fruit dry weights. Accordingly, treatments that improved considerably K-uptake by plants (the combination between foliar application of amphora extract + 5 g kg-1 biochar + 0-3 g kg-1 compost) recorded the highest improvements in productivity of zucchini plants.