Effects of mulching on soil temperature and moisture variations, leaf nutrient status, growth and yield of pistachio trees (Pistacia vera.L)

The objective of this study was to investigate the response of leaf nutrients concentration, growth and yield of pistachio trees affected by changes in soil moisture and temperature as a result of different mulching. The experiment was conducted in a randomized complete block design with five replications in Feyzabad, Khorasan Razavi, Iran, for two years in 2014 ('off' year) and 2015 ('on' year). Treatments included sub-soil plastic (SPM1 and SPM2), up-soil plastic (UPM), woodchips (WM), barley residue (BM) mulches and control (CK). Treatment of SPM2 recorded the highest shoot growth and nut splitting, and lowest bud abscission in 'off' year. However, in 'on' year, maximum bud abscission was found in SPM2. Treatments of BM and WM were effective in decreasing flower bud and fruit abscission than other treatments during 'on' year. Mulching affected leaf P concentration in 'off' year and N, P and Mg in 'on' year, with the highest rate of these nutrients recording in BM treatment. Yield variations were not significantly affected by treatments in 'off' year, but in 'on' year, SPM2, WM, BM and SPM1 treatments increased yield by 29.2%, 28.7%, 19.8% and 10.5% compared to CK, respectively. Unlike other treatments, UPM had negative effect on leaf N concentration, and yield during 'on' year. This difference is attributed to high soil temperature in this treatment, so that yield reduced in soil temperature ranges over 36-37 °C in mean depth of 20-60 cm. In general, sub-soil plastic mulches, despite increasing yield in 'on' year, could not control flower bud abscission in that year. Thus, due to the increase of leaf nutrient concentration, regulation of alternate bearing phenomenon and improvement of yield, organic mulches are better options in arid and semi-arid regions with traditional irrigation methods.