Rosa chinensis Jacq. var. mutabilis plants were grown in a greenhouse to determine whether a hand-held chlorophyll meter (SPAD-meter) is suitable for the plant N status assessment. Therefore, plants were fertilized with increasing levels of N, applied through urea form as top dressing. The doses were: 0, 0.15, 0.3, 0.45, 0.6, and 0.75 g of N per liter of substrate. Periodically during the growing season, plant height and width, fresh and dry weight of different plant organs at 10, 20, and 30 weeks after planting, and their total N, plant P, and K were measured. Furthermore, six times along the growing cycle, the amount of chlorophyll in leaves was estimated using a SPAD-meter and analytically measured by chlorophyll extraction with ethanol and reading through a spectrophotometer. In the same leaves, N concentration was also determined. Treatments with 0.45–0.6 g of N per liter of substrate gave the tallest and widest plant. Plant weight and flower production were also the highest with these doses. The concentration of organic N in plant organs increased along with the N availability in the substrate, which suggests that a “luxury consumption” took place. The SPAD values showed high correlation among chlorophyll and N concentrations. Values that ranged between 35–40 seemed to mean good nutrient status. A high correlation was also found among SPAD values and some of the productive characteristics, which indicates that a SPAD-meter is a suitable tool in the dynamic fertilization of rose.
Giampaolo Zanin and Paolo Sambo
Giampaolo Zanin and Paolo Sambo
Liatris is an ornamental plant cultivated as a garden perennial for more than 70 years. Since the early 1970s, Liatris spicata has gained importance as a cut flower because of its long-lasting flowering and its peculiar downward flowering succession. This species is usually cultivated in beds both outdoors and in greenhouses. However, in order to improve yield and quality production, some research has been carried out on soilless cultivation. In particular, floating systems seem to provide the best performances, although only different nutrient solutions or their concentrations have been studied. In this research, in addition to two different concentrations of Hoagland solution [full-strength (H) and a half-strength (1/2H)], three corm circumferences (8/10, 10/12, and 12+) and three plant densities (36, 48, and 60 plants/m2) were also evaluated. The full-strength solution gave the best performance from both qualitative and quantitative standpoints. This nutrient solution also showed, at the end of the experiment, very high residual nitrate-N, which could induce environmental pollution during disposal. Furthermore, the management of the solution appeared more difficult and time-consuming. All these aspects should be taken into account by growers in making choices. Corm size also affected production. Increasing circumference from 8/10 to 12+ increased marketable stems per plant and their quality traits, but, because of the highest mortality of plants observed with the bigger corms, yield per square meter did not increase over corm size of 10/12. Finally, rising plant density from 36–60 plants/m2, the biomass of the single plant decreased. However, it resulted also in the enhancement of sellable production per square meter.
Paolo Sambo, Franco Sannazzaro, and Michael R. Evans
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.
Paolo Sambo, Giorgio Gianquinto, and Valente Forte
Several experiments on multispectral radiometer showed its suitability in driving nitrogen fertigation in tomato crop. Nir-Green light ratio describes crop nitrogen status well, highlighting element deficiency or excess, which is a great help to farmers in choosing timing and intensity of fertilizer application. The scientific literature reports several studies about nitrogen management only, but not phosphorus and potassium. Because of the advantage obtained with N, it would be desirable to also adapt it to phosphorus and potassium management. For this purpose, a preliminary trial was carried out on the omato cultivar Brigade grown in pots in a greenhouse. Four nutrient solution were supplied. Three were lacking in N, P, or K—the last had all elements needed for a balanced growth. Radiometer readings were taken once a week during the crop cycle, around noon. First results were encouraging. After some data elaboration, it appeared evident that, in some cases, it was possible to set the fertigation treatments apart by only having a look at the single wavelengths measured by the instrument. Through the Nir/green index, used in N management, phosphorus deficiency was identified as well. Potassium trend line was completely different from those of nitrogen and phosphorus, and very similar to that of the control. The utilization of the radiometer in handling potassium fertigation in tomato appeared somewhat difficult. Its application might be desirable, instead, for phosphorus fertigation in addition to nitrogen. The 560 and 710 nm wavelengths might be the especially more useful for this purpose, although a simple index or a combination of some simple indices able to identify phosphorous deficiency/excess and to screen them from those induced by nitrogen are needed.
Paolo Sambo*, Daniele Borsato, and Giorgio Gianquinto
Research at Padova Univ., Italy, during Summer 2003, was carried out to determine the effect on nitrogen fertilization on yield and canopy reflectance of sweet bell pepper (Capsicum annuum). Pepper var. Tolomeo LRP 4993 (Syngenta) was transplanted into plots (24 m2) on 20 May, maintaining 40 cm between plants and 75 cm between rows (3.3 plant per m2). The experimental design was a randomized block with four replicates. Treatments were 6 nitrogen fertilization rates ranging from 0 to 300 kg·ha-1. Nitrogen was distributed at planting and as top dressing, 44 days after planting. All other production techniques were typical of pepper production in the Veneto region. Beginning the second week after transplanting, canopy reflectance was measured weekly using a multispectral radiometer MSR 87 (Cropscan Rochester, Minn.). Fruits were harvested at breaking color stage starting from 21 July to 9 Oct. (8 harvests). At harvest, total and marketable yield, fruit averaged weight and nitrogen content were determined. Maximum yield was recorded at the 120 kg·ha-1 nitrogen treatment, while higher rates proved ineffective at increasing production. Nitrogen rates positively affected fruit weight. The nitrate content of fruits also increased with the nitrogen rates although it remained below the level dangerous for human health. Canopy reflectance was able to detect the different nitrogen treatments only during the late stages of the growth cycle making difficult its use as a tool to drive nitrogen fertilization.
Paolo Sambo, Franco Sannazzaro, and Michael Evans
In order to evaluate alternative rooting media as a substitute to sphagnum peat in tomato transplant, fresh rice hulls (2 and 4 mm particle size), perlite, and peat were compared. In the same experiment, four nutrient solutions differing in electrical conductivity [(EC) 2.5, 3.5, 4.5 and 6.0 mS/cm], but not in nutrient content, were used. Seed of tomato (Lycopersium esculentum L.) `Brigade' (ASGROW) were sown in 55 × 35 × 6.5 cm polystyrene transplant trays containing 336 cells (15 mL) and filled with the root substrates. The trays were placed in a glass-glazed greenhouse. Trays were kept under intermittent mist for 6 days and then fertilized twice per week with 2.6 L per tray of solution. A split-plot design with three replications was used with nutrient solution serving as the main plot and root substrates serving as the subplots. During the growing cycle (once a week) and when plants were ready to transplant (16 cm tall, with an average of five to seven true leaves), stem diameter, hypocotyl length, plant height, number of true leaves, fresh shoot weight, and dry shoot weight were measured. Also at transplant, root fresh and dry weight and above- and below-ground biomass were analyzed to determine N, P, K, Ca, Mg, Fe, and Mn content. Plants grown in rice hulls were as marketable as those in peat, but showed a higher content in N, K, and Mn. Increased nutrient solution affected not only dry matter accumulation, but also stem diameter and plant hight, which were greater in plants grown with high EC.
Paolo Sambo, Mike R. Evans, and Giorgio Gianquinto
One of the most widely used substrates in nursery production is peat, which is used as plain substrate or mixed with other media. Peat use is problematic, primarily because of the high price and the environmental implications connected with its extraction and disposal. For these reasons, the exploitation will be restricted in the future in both Europe and America. Thus, researchers are under pressure to find alternative substrates that can be used in an inexpensive and environmentally friendly way. Although aged, carbonized and composted rice hulls have been used to a limited extent, more studies are needed to characterize fresh rice hulls as a growing medium. This research was aimed at characterizing fresh hulls after being ground in different particle sizes, and comparing them with peat. Ground hulls were separated into four fractions (6-, 4-, 2-, and 1-mm diameter), which were characterized for pH, EC, CEC, organic matter, and total nitrogen content. The water retention curve was also estimated and the following hydraulic characteristics were measured and compared: TP, CC, AFP, EAW, and WBC. As expected, pH, N, and C content and CEC did not differ among rice hull fractions, while EC showed a slight but constant increase when particle dimensions decreased. Compared to peat, the TP of rice hulls was smaller independently from particle dimensions, but AFP was 19.5%, 44,1%, 114.2%, and 115.8% higher for 1-, 2-, 4-, and 6-mm particles, respectively, indicating a very good aeration capacity. EAW and WBC were higher only in 1- and 2-mm particles. A further experiment aimed at comparing the behavior of transplants in rice hulls (6 mm) and peat showed that tomato plantlets grew slower in the former, although transplants were of good, marketable quality.
Johann S. Buck, Michael R. Evans, and Paolo Sambo
Horticultural root substrates are designed to provide the optimal physical properties for plant growth. These properties include bulk density (g·cm-3), air-filled pore space (% v/v), total pore space (% v/v), water-filled pore space (% v/v), water-holding capacity (% v/v and w/w), and wettability. Whole, fresh parboiled rice hulls were ground to produce four grades with varying particle size distributions. Particle sizes for the four grades ranged from <0.25 to >2.80 mm. Additionally, discrete particle sizes of <0.25, 0.50, 1.00, 2.00, 2.80, and >2.80 mm were produced. For all grade distributions and particle point sizes, physical properties were determined and contrasted against Canadian sphagnum peat. As the proportion of smaller particle sizes in the distributions increased or as the particle point sizes decreased, total pore space (% v/v) and air-filled pore space (% v/v) decreased, while, bulk density (g·cm-3) and water-holding capacity (% v/v and w/w) increased. Additionally, as the proportion of particle sizes from <0.25–0.50 mm increased, the wettabilty of the whole fresh parboiled rice hull material decreased. Particle sizes ranging from 1.00–2.80 mm possessed the physical properties most suitable for plant growth in containerized greenhouse crop production and were most similar to peat.
Giorgio Gianquinto, Paolo Sambo, Francesco Orsini, Marco Sciortino, and Valente Forte
Technology provides new tools for agriculture to be able to optimize fertilization. Optical instruments are becoming valid tools for farmers in making decisions about fertilization, even though they need to be calibrated for specific crops. Chlorophyll meters and multispectral radiometers have been tested on rice, corn, and wheat and afterwards on vegetables, in timing fertilization. Today, threshold lines that are able to detect crop N status in tomato crops are available. These thresholds, obtained in experiments carried out at Padova University, were validated in three open-field experiments. The first experiment was carried out in 2004 at the University experimental farm on tomato cv. Perfect Peel. The second and third experiments were conducted in a commercial farm at Codigoro (Ferrara) in 2004–2005. Tomato cultivars used were `UGX 822' and `Precocix' in 2004, in 2005 `Jet' was also used. In all trials, a “standard fertilization” management was compared with fertigation guided using SPAD and/or Cropscan. Optical tools were used to manage fertigation adopting both “threshold method” and “reference plot method”. In general “guided fertigation” resulted in less nitrogen application (N supply reduced between 18% and 45%), especially when “threshold method” was adopted. Yields were comparable to “standard fertilization” treatments, showing a better efficiency of “guided fertigation”. In some cases, guiding fertigation by means of optical instruments allowed higher fruit fresh weight, although dry matter content and °Brix were not influenced. Guided fertigation reduced also the number of damaged fruit and the percentage of nonmarketable product.
Giorgio Gianquinto, Francesco Orsini, Paolo Sambo, and Matilde Paino D'Urzo
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.