Growth and nut yield of plastic mulched pecan trees growing under hot and dry conditions

Five-year-old 'Wichita' pecan trees growing under hot and dry conditions of the Sonoran desert in the northwest of Mexico were plastic mulched on March 25, 2013 to evaluate its effect on plant growth and nut yield. Trees were planted in a rectangular design and space between rows and trees was 12 by 6 m, respectively. Tree rows were hedged North-South. The area between rows was mowed to clean the alleys during the growing season. Fall leaves were accumulated under tree canopies over the soil, making a natural mulch of 2 cm height. Irrigation was provided with subsurface drip irrigation with four lines, ≈1.5 and 3 m at each side of the row center running the length of the row with 1.8 L h^‑1 emitters spaced 0.5 m apart. In this study two treatments were tested, plastic mulch (PM) and the control (CO, no plastic mulch). The PM treatment consists in place over the drip lines, above soil surface, a one-meter wide white plastic band; it means four bands per row (24 m² tree^‑1). Control treatment was not plastic mulched. In the beginning of February, a set of capacitance probes (EC-5, Decagon) were placed at 10, 30, 60, 90 and 120 cm depth, between two drip lines, and the information was recorded with a data logger. The experimental design was a randomized complete block with four replications. Each experimental plot consisted in a row of 15 trees. Total nut yield and marketable yield and viviparous nut yield was not significantly different in both treatments. Cumulative total nut yield in PM treatment was 5,364 kg ha^‑1, 9.6% higher than control treatment. Nut yield efficiency, expressed as g of nuts produced by each square cm of the trunk transversal area, was higher in PM treatment, but it was not significantly different. In 2014, PM treatment increased significantly nut vivipary yield in 2014, from 237 to 386 kg ha^‑1. Percent of viviparous nuts varied from 15.9 to 24.1% in both years of study; PM had higher values, but there were no significant differences. Regarding to nut quality, there were no significant differences on total meat yield, premium meat yield and embryo rot. In 2013, PM treatment increased significantly nut weight (from 8.30 8.47 g nut^‑1). Fruiting characteristics as percent of shoot with cluster, fruits per cluster and fruits per shoot were not affected significantly. In high a yielding year, 2013, percent of shoot with cluster oscillated from 76.5 in the control treatment to 81.0% in PM treatment. Also in low yielding year, 2014, fruit per cluster and fruit per shoot was lower, in both treatments. During the period of March 12 to May 7, 2014, PM increased soil volumetric water content (m³ of water m^‑3 of soil), was increased in the next soil depths: 10 cm depth (from 0.30 to 0.34 m³ m^‑3), 30 cm (from 0.35 to 0.4 m³ m^‑3), 60 cm (0.32 to 0.25 m³ m^‑3). In this study, mulched soil had 14% more water content than control treatment. Plastic mulch decreased water loss avoiding soil evaporation and also affected nut quality and shoot retention.