EFFECT OF SPENT MUSHROOM SUBSTRATE ON THE GROWTH AND YIELD OF THREE CULTIVARS OF MUSKMELONS (Cucumis melo)

Muskmelons are currently grown in several areas of Vietnam for domestic and international consumer markets. The fruit grows well in greenhouses in soil or soilless substrate such as coconut peat. Researchers in Vietnam are investigating the growth of muskmelons in a range of organic by-products. In this study, spent mushroom substrate was recycled for use as an organic substrate and to evaluate the growth, quality, and yield of three muskmelon varieties including RZ F1, PN 128, and TL3 in greenhouses over three months. The substrate was incubated for one month before use and contained 45% spent mushroom substrate, 30% manure, 7.7% rice husks, 1.5% phosphorus, 0.2% commercial Trichoderma (Tribac), 0.1% rice bran, 15% sand, and 0.5% micronutrients and water. Following incubation, the substrate had optimal pH for the growth of muskmelon and the concentration of nutrients and beneficial microorganisms had increased significantly. The growth of RZ F1 and TL3 cultivars was significantly better than PN 128 in terms of growth, fruit quality, and yield. Specifically, RZ F1 and TL3 species took 78 days and 75 days to complete their life cycle produced 1.76 kg and 1.62 kg of fruit, had a pericarp thickness of 4.0 cm, and possessed 14.20o Brix and 14.88o Brix of soluble solid content, respectively. These findings suggest that agricultural by-products, such as spent mushroom substrate, could be a valuable resource for the culture of muskmelons in Vietnam.

Calcium Carbonate Can Be Used to Manage Soilless Substrate pH for Blueberry Production

Blueberry (Vacciniumcorymbosum interspecific hybrids) production in soilless substrates is becoming increasingly popular. Soilless substrates have low pH buffering capacity. Blueberry plants preferentially take up ammonium, which acidifies the rhizosphere. Consequently, soilless substrates where blueberry plants are grown exhibit a tendency to get acidified over time. Agricultural lime (CaCO3) is commonly used to raise soil and substrate pH in other crops, but it is rarely used in blueberry cultivation. We hypothesized that substrate amendment with low rates of agricultural lime increases substrate pH buffering capacity and provides nutritional cations that can benefit blueberry plants. We tested this hypothesis in a greenhouse experiment with ‘Emerald’ southern highbush blueberry plants grown in rhizoboxes filled with a 3:1 mix of coconut coir and perlite. We found that substrate amendment with CaCO3 did not cause high pH stress. This amendment maintained substrate pH between 5.5 and 6.5 and provided Ca and Mg for plant uptake. When blueberry plants were grown in CaCO3-amended substrate and fertigated with low pH nutrient solution (pH 4.5), they exhibited greater biomass accumulation than plants grown in unamended substrates. These results suggest that low rates of CaCO3 could be useful for blueberry cultivation in soilless substrates.

Petunia (Petunia ×hybrida) Cultivars Vary in Silicon Accumulation and Distribution

Silicon (Si) is a plant-beneficial element that can alleviate the effects of abiotic and biotic stress. Plants are typically classified as Si accumulators based on foliar Si concentrations (≥1% Si on a dry weight basis for accumulators). By this definition, most greenhouse-grown ornamentals are low Si accumulators. However, plants that accumulate low foliar Si concentrations may still accumulate high Si concentrations elsewhere in the plant. Additionally, screening cultivars for variability in Si uptake has not been investigated for low Si accumulator species. Therefore, the objective of this study was to assess cultivar variability in Si accumulation and distribution in petunia (Petunia ×hybrida). Eight cultivars (Supertunia Black Cherry, Supertunia Limoncello, Supertunia Priscilla, Supertunia Raspberry Blast, Supertunia Royal Velvet, Supertunia Sangria Charm, Supertunia Vista Silverberry, and Supertunia White Improved) were grown in a commercial peat-based soilless substrate under typical greenhouse conditions. They were supplemented with either 2 mm potassium silicate (+Si) or potassium sulfate (-Si) at every irrigation. Silicon supplementation increased leaf dry mass (4.5%) but did not affect total dry mass. In plants not receiving Si supplementation, leaf Si ranged from 243 to 1295 mg·kg−1, stem Si ranged from 48 to 380 mg·kg−1, flower Si ranged from 97 to 437 mg·kg−1, and root Si ranged from 103 to 653 mg·kg−1. Silicon supplementation increased Si throughout the plant, but most predominantly in the roots. Leaf Si in the 2 mm Si treatment ranged from 1248 to 3541 mg·kg−1 (173% to 534% increase), stem Si ranged from 195 to 654 mg·kg−1 (72% to 376% increase), flower Si ranged from 253 to 1383 mg·kg−1 (74% to 1082% increase), and root Si ranged from 4018 to 10,457 mg·kg−1 (593% to 9161% increase). The large increase in root Si following supplementation shifted Si distribution within plants. In nonsupplemented plants, it ranged from 51.2% to 76.8% in leaves, 8.2% to 40.2% in stems, 2.8% to 23.8% in flowers, and 1.2% to 13.8% in roots. In Si-supplemented plants, it ranged from 63.5% to 67.7% in leaves, 10.5% to 22.6% in roots, 9.4% to 17.7% in stems, and 1.6% to 9.6% in flowers. This study indicates that petunia, a low foliar Si accumulator, can accumulate appreciable quantities of Si in roots when provided supplemental Si.

The Use of Dewpoint Hygrometry to Measure Low Water Potentials in Soilless Substrate Components and Composites

Plant water availability in soilless substrates is an important management consideration to maximize water efficiency for containerized crops. Changes in the characteristics (i.e., shrink) of these substrates at low water potential (<−1.0 MPa) when using a conventional pressure plate-base can reduce hydraulic connectivity between the plate and the substrate sample resulting in inaccurate measures of water retention. Soilless substrate components Sphagnum peatmoss, coconut coir, aged pine bark, shredded pine wood, pine wood chips, and two substrate composites were tested to determine the range of volumetric water content (VWC) of surface-bound water at water potentials between −1.0 to −2.0 MPa. Substrate water potentials were measured utilizing dewpoint hygrometry. The VWC for all components or composites was between 5% and 14%. These results were considerably lower compared to previous research (25% to 35% VWC) utilizing conventional pressure plate extraction techniques. This suggests that pressure plate measurements may overestimate this surface-bound water which is generally considered unavailable for plant uptake. This would result in underestimating available water by as much as 50%.

Comparison of Water Capture Efficiency through Two Irrigation Techniques of Three Common Greenhouse Soilless Substrate Components

Substrate wettability is an important factor in determining effective and efficient irrigation techniques for container-grown crops. Reduced substrate wettability can lead to lower substrate water capture, excessive leaching and poor plant growth. This research examined substrate water capture using surface and subirrigation under three initial moisture contents (IMC). Sphagnum peat moss, coconut coir, and pine bark were tested at IMCs of 67% 50%, and 33%. Substrate water capture was influenced by both IMC and irrigation technique. Surface irrigation increased the water capture of coir and peat, regardless of IMC, whereas IMC influenced pine bark water capture more than irrigation method. Surface-irrigated coir at or above 50% IMC provided the greatest water capture across all treatments. The first irrigation had the highest capture rate compared to all other events combined. Container capacities of pine bark and coir were unaffected by IMC and irrigation type, but the CC of peat was less by ~ 40% volumetrically under low IMC conditions. Coir, had the greatest ability to capture water, followed by pine bark and peat, respectively. Moisture content, irrigation type and component selection all influence the water capture efficiency of a container substrate.