Rabets (Raised Bed Trough System)
The Rabets field trials were initiated at Monterey Bay Academy (MBA) near Watsonville, CA and near Santa Maria, CA in Fall 2010 to Summer 2011. The studies were set-up in randomized complete block design consisting of 5 treatments replicated 4 times. The treatments were 1.) 100% coir, 2.) 70:30 peat:perlite mixture, 3.) 50% steamed soil + 50% amendments (25% rice hulls + 25% coir), 4.) fumigated grower’s standard and 5.) non-fumigated grower standard. Harvesting was done from April 28 to September 15, 2011(MBA) and April 13 to October 4, 2011 (Santa Maria) and the fruits were sorted as marketable and cull (non-marketable). Periodic collection of substrate samples was done to monitor pH, electrical conductivity (EC), nitrate-N (NO3-N), ammonium-N (NH4-N) and available P. All data were subjected to analysis of variance (JMP version 8) and LSD at 0.05 was used to compare means. Table 2 shows the diameter and yield of strawberry grown in Monterey Bay Academy (MBA) and Santa Maria. There were highly significant differences in diameter and yield (marketable, cull and total) of strawberry grown in Monterey Bay Academy. The widest diameter (10.46 in) was from plants grown in peat:perlite system. The three different substrates (coir, peat:perlite and amended soil) did not significantly differ in terms of marketable yield. The standard untreated control treatment had the smallest diameter and lowest marketable yield. The percent marketable yield of the amended soil, coir and peat:perlite treatments were significantly higher by 13%, 27% and 29%, respectively, relative to the fumigated standard treatment. In Santa Maria, the widest plant diameter (10.25 in) was in the amended soil and peat:perlite substrate. However, the different growing media did not significantly affect the marketable yield. Significant differences were only noted on the cull yield. The highest cull yield was from the amended soil. The significantly higher cull yield obtained from the amended soil treatment, both in Santa Maria and MBA could be attributed to the very low pH and high EC of this substrate.
One of the main concerns in soilless strawberry production is the maintenance of a favorable pH, EC and nutrient supply to the growing plants; thus, periodic sampling was done. For most of the sampling periods at both experimental sites, the different substrate and soil treatments were significantly different in terms pH, EC, NO3-N, NH4-N and available P. The results of analysis for NO3-N are shown in Table 3. At both sites, the pH of coir and peat:perlite treatments was lower in the early sampling periods but increased with time reaching the targeted value of 5.7. It took 3 to 4 months (pH data of some sampling periods not shown) for the pH to equilibrate and reach the target value which could be attributed to the high buffering capacity of the soilless substrates. The pH of the amended soil treatments at both sites were generally low at all sampling periods and the target value was not reached. With the exception of the initial sampling period, the ECs of the substrate treatments at MBA were generally low (<2.0 mS/cm). In contrast, the ECs in Santa Maria were consistently high which could be due to the higher amount of salts in the irrigation water. The EC of the amended soil treatment in Santa Maria was also consistently high throughout the growing season. The soilless substrates are considered to be low in nutrients; thus, fertilization is one of the key issues in using these for strawberry production. Surprisingly, the initial NO3-N of the 100% coir and peat:perlite mixture was higher at both sites and the target value of 100 ppm was maintained in beds through the season except for the latter stages of plant growth. The grower’s standard beds had generally low NO3-N. At all sampling periods, the NH4-N was lower than the RABETs target value of 14 ppm. The RABETs target available P of 30 ppm was maintained in all of the media treatments at both sites.