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  • Author or Editor: Paolo Sambo x
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Ground fresh rice (Oryza sativa) hull materials were produced by grinding whole fresh rice hulls and passing the resulting product through a 1-, 2-, 4- or 6-mm-diameter screen to produce a total of four ground rice products (RH1, RH2, RH4, and RH6, respectively). The physical properties and water release characteristics of sphagnum peatmoss (peat) and the four ground rice hull products were evaluated. All of the ground rice hull products had a higher bulk density (Bd) than peat, and as the grind size of the rice hull particle decreased, Bd increased. Peat had a higher total pore space (TPS) than all of the ground rice hull products except for RH6. As grind size decreased, the TPS decreased. Peat had a lower air-filled pore space (AFP) than all of the ground rice hull products and as the grind size of the rice hull products decreased, AFP decreased. Peat had a higher water holding capacity (WHC) than all of the ground rice hull products. Grind sizes RH4 and RH6 had similar WHC, whereas RH1 and RH2 had a higher WHC than RH4 and RH6. Peat, RH4, and RH6 had similar available water content (AVW), whereas RH2 had higher AVW than these materials and RH1 had the highest AVW. However, peat had the lowest AVW and easily available water (EAW) as a percentage of the WHC. The ground rice hull products RH1 and RH2 had the highest AVW and EAW of the components tested. Peat had the highest water content at container capacity. As pressure was increased from 1 to 5 kPa, peat released water more slowly than any of the ground rice hull products. The RH1 and RH2 ground hull products released water at a significantly higher rate than peat, but RH4 and RH6 released the most water over these pressures. For all rice hull products, most water was released between 1 and 2 kPa pressure. The rice hull products RH1 and RH2 had physical properties that were within recommended ranges and were most similar to those of peat.

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Dynamic fertilization management is a way of bringing nutrients to the plant when they are crucial for its development. However, destructive measurements of crop nitrogen (N) status are still too costly and time consuming to justify their use, and the implementation of methodologies based on non-destructive, quick, and easy to use tools for plant nutritional status monitoring appears as an appealing opportunity. Several optical tools for plant monitoring have been developed in recent years, and many studies have assessed their ability to discriminate plant N status. Such tools can measure at leaf level (hand-held optical instruments) or may consider the canopy of a plant or few plants (portable radiometers) or even measure areas, such as a field, a farm, or a region (aerial photography). The application of vegetation indices, which combine the readings at different wavelengths, may improve the reliability of the collected data, giving a more precise determination of the plant nutritional status. In this article, we report on the state of the art of the available optical tools for plant N status monitoring.

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The primary objective of this research was to compare the pH, electrical conductivity (EC), and primary macronutrient status of three ground parboiled fresh rice hull (PBH) products to sphagnum peat when used as a root substrate over 56 days in a greenhouse environment. The three grades of ground rice hull products were produced by grinding PBH and passing the ground product through different screens. One grade (P3) was passed through a 2.00-mm screen and captured on a 1.00-mm screen. The second grade (P4) was passed through a 1.00-mm screen and captured on 0.50-mm screen. A third ground rice hull product (RH3) was a commercially available, ground PBH material that was ground in a hammer mill until it passed through a screen with 1.18-mm-diameter openings and was collected on a screen with 0.18-mm openings. The pH of sphagnum peat ranged from 3.4 to 3.7 across time. The pH of RH3 and P3 increased from 4.7 to 7.1 on day 5 and 14, respectively, before decreasing to 6.3 and 6.7, respectively, on day 56. The pH of P4 increased from 4.8 to 6.9 on day 6 before decreasing to 6.6 on day 56. The P4 had an EC of 1.2 dS·m−1, which was higher than that of peat, RH3, and P3, which had similar EC of 0.7 to 0.8 dS·m−1 regardless of time. The ammonium (NH4 +) concentration was unaffected by time. Peat had an NH4 + concentration of 6.4 mg·L−1, which was lower than that of the ground rice hull products. The P3 had an NH4 + concentration of 14.6 mg·L−1, which was higher than that of RH3 and P4. The RH3 and P4 had similar NH4 + concentrations of 11.8 and 10.8 mg·L−1, respectively. The nitrate (NO3 ) concentration was unaffected by time. The RH3 had a NO3 concentration of 8.2 mg·L−1, which was significantly higher than that of peat, P3, and P4, which had similar NO3 concentrations of 0.5 mg·L−1. The phosphorus (P) concentration in peat ranged from 1.3 to 2.5 mg·L−1 across the sampling times, and peat had a lower P concentration than all rice hull products, which ranged from 57.4 to 104.4 mg·L−1. The potassium (K) concentration in peat ranged from 2 to 5 mg·L−1 across the sampling times and was always lower than that of the rice hull products, which had a K concentration ranging from 195 to 394 mg·L−1. Because pH, P, and K concentrations were above recommended concentrations, ground rice hull products would not be suitable as a stand-alone substrate but might be amended with materials such as elemental sulfur or iron sulfate to adjust the pH or blended with other components to reduce the P and K concentrations to within recommended concentrations.

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