Guihong Bi

Spring growth of almond nursery trees depends upon nitrogen from both plant reserves and spring fertilizer application

Summary June-budded ‘Nonpareil’/‘Nemaguard’ almond (Prunus dulcis (Mill) D. A. Webb) trees were fertigated with one of five nitrogen (N) concentrations (0, 5, 10, 15, or 20 mM) from July to September. The trees were sprayed with either water or 3% urea in October, then harvested bareroot after natural leaf fall, and stored at 2°C. One set of trees was destructively sampled for total N content; the remaining trees were transplanted into N-free media in the spring after cold storage. After budbreak, these trees were supplied for 70.d with either N-free Hoagland’s solution or Hoagland’s solution containing 15N-NH4NO3. Nitrogen concentrations in both stem and root tissues were positively correlated with the N-fertigation concentration. Fall foliar urea applications increased levels of stem and root N regardless of the N-fertigation concentration. During the first 70 d of spring growth, the trees utilized nitrogen from both their reserves and spring fertilizer applications. The amount of N reserves used for growth of new shoots and leaves was proportional to the total amount of reserves. Trees with low N reserves relied primarily on the spring fertilizer as their source of nitrogen. We conclude, therefore, that both reserve N and spring-applied N fertilizers are important for enhancing the regrowth of bareroot almond nursery trees during establishment after transplanting. Nitrogen fertilization in the spring can especially improve the performance of trees with low N reserves.

Soil and foliar nitrogen supply affects the composition of nitrogen and carbohydrates in young almond trees

Summary June-budded ‘Nonpareil/Nemaguard’ almond (Prunus dulcis (Mill) D. A. Webb) trees were fertigated with one of five nitrogen (N) concentrations (0, 5, 10, 15, or 20 mM) in a modified Hoagland’s solution from July to September. In October, the trees were sprayed twice with either water or 3% urea, then harvested after natural leaf fall and stored at 2°C. Trees were destructively sampled during winter storage to determine their concentrations of amino acids, protein, and non-structural carbohydrates (TNC). Increasing N supply either via N fertigation during the growing season or with foliar urea applications in the fall increased the concentrations of both free and total amino acids, but decreased their C/N ratios. Moreover, as the N supply increased, the proportion of nitrogen stored as free amino acids also increased. However, protein was still the main form of N used for storage. The predominant amino acid in both the free and the total amino-acid pools was arginine. Arginine N accounted for an increasing proportion of the total N in both the free and the total amino acids as the nitrogen supply was increased. However, the proportion of arginine N was higher in the free amino acids than in the total amino acids. A negative relationship was found between total amino acid and non-structural carbohydrate concentrations, suggesting that TNC is increasingly used for N assimilation as the supply of nitrogen increases. Urea applications decreased the concentrations of glucose, fructose, and sucrose, but had little influence on concentrations of sorbitol and starch. We conclude that protein is the primary form of storage N, and that arginine is the predominant amino acid. Furthermore, the synthesis of amino acids and proteins comes at the expense of non-structural carbohydrates.

Effects of copper, zinc and urea on defoliation and nitrogen reserves in nursery plants of almond

Summary ‘Nonpareil’/‘Nemaguard’ and ‘Nonpareil’/ ‘Lovell’ almond (Prunus dulcis (Mill) D. A. Webb) nursery trees were used to study the effects of foliar applications of CuEDTA (Cu), ZnSO4 (Zn) and urea on defoliation and nitrogen (N) reserves. Foliar application of Cu and Zn induced early defoliation, with one spray as effective as two. Trees receiving Cu were defoliated 20–30 d before controls and defoliation on trees sprayed with Zn occurred 10–14 d before controls. Urea increased the efficiency of defoliation by Zn (1.25–2% ZnSO4) and Cu (0.5% CuEDTA). Trees receiving defoliants contained 4–26% less N than naturally defoliated controls, and N reserves were higher in trees given urea than in controls. Trees sprayed with urea plus defoliants contained up to 20% more N than controls. Both CuEDTA and ZnSO4 promoted early defoliation in almond trees, while the addition of urea can assist in maintaining tree N reserves.

Planting Date Effect on Yield of Tomato, Eggplant, Pepper, Zinnia, and Snapdragon in High Tunnel in Mississippi

‘High tunnels’ are unheated greenhouse structures used to extend the growing season and protect high-value horticultural crops. High tunnels have been used for many years worldwide and their popularity has increased in Mississippi recently. A planting date study of ‘Roma’ tomato (Solanum lycopersicum L.), ‘Legend’ tomato, ‘Ichiban’ eggplant (Solanum melongena L.), ‘Sweet Banana’ pepper (Capsicum annuum L.), ‘Benarys Giant’ zinnia (Zinnia elegans L.), and ‘Potomac Red’ snapdragon (Antirrhinum majus L.) was conducted in 2010 in three high tunnels in Starkville, Mississippi. Each vegetable and cut flower cultivar was treated as an independent study. There were two planting dates for all the cultivars: 12 March 2010 and 2 April 2010. Only for zinnias, yield (272 stem/plot) of first planting date was higher than planting date two (106 stem/plot). A significant block effect was observed with ‘Legend’ tomato and ‘Ichiban’ eggplant where one high tunnel had significantly higher yield than the other two high tunnels. Harvesting of tomato, eggplant, and pepper from high tunnels was a month earlier than the field-grown crops. High tunnels can extend the growing season to provide produce to the market at earlier harvest dates in Starkville, Mississippi.

Rate of nitrogen application during the growing season alters the response of container-grown rhododendron and azalea to foliar application of urea in the Autumn

Summary One-year-old rhododendron (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron ‘Cannon’s Double’) plants grown at different nitrogen (N) fertilisation rates were used to assess the influence of soil N applications during the growing season, and foliar applications of urea in the Autumn, on N uptake and accumulation, and plant growth in the following Spring. N uptake efficiency declined linearly during the first growing season with an increasing rate of N fertilisation. For both cultivars, foliar urea application in the Autumn significantly increased plant N content without affecting plant size, regardless of plant N status. Leaves of rhododendron accumulated more N than other plant structures. Plants sprayed with foliar urea in the Autumn had more new growth the following Spring than plants receiving no urea, regardless of whether the plants received fertiliser in the Spring. For azalea, N uptake in the Spring was, in general, not affected by applications of urea during the previous year. For rhododendron, urea application in the Autumn decreased N uptake the following Spring. For both cultivars, increasing N availability during the growing season increased the ratio of above-ground to below-ground dry weight. Our results suggest that combining optimum N applications during the growing season with foliar application of urea in the Autumn can improve N uptake efficiency, increase N storage, and optimise growth in Rhododendron.

Effects of spring soil nitrogen application on nitrogen remobilization, uptake, and partitioning for new growth in almond nursery plants

Summary One year old ‘Nonpareil’ almond (Prunus dulcis (Mill) D. A. Webb) trees on ‘Lovell’ rootstocks were used to evaluate the effects of soil nitrogen (N) availability in the spring on N remobilization, uptake, partitioning, and tree growth. After being transplanted to an N-free medium, the trees received a modified Hoagland solution, with or without N from 15N-depleted NH4NO3, twice a week for 12 weeks. During the first four weeks, the N used for new shoot and leaf growth mainly came from the nitrogen that had accumulated in storage tissues. No significant differences were seen in the amount and duration of N remobilization between N-fertilized trees and those that received no N. However, trees that were fertilized in the spring had significantly more new shoot and leaf growth. Uptake of 15N by the roots began two weeks after transplanting. Nitrogen was rapidly taken up from the soil during the period of greatest shoot and leaf growth; leaves were the major sink for N from both root uptake and storage. Six weeks after transplanting, the whole-tree N content was significantly higher in fertilized trees than in the controls. We conclude that the remobilization of N for spring new growth takes place irrespective of the current-year external N supply. However, the new growth in young almond trees is highly dependent on soil N availability, which demonstrates the importance of spring N fertilizer applications following transplantation.

ADDITION OF PULP MILL ASH RAISES PH, MODIFIES PHYSICAL PROPERTIES, AND ALTERS YOUNG TOMATO PLANT GROWTH AND MINERAL NUTRITION IN A PEAT-BASED SUBSTRATE

Pulp and paper mills often burn wood waste to fuel their boilers. The ash from a Mississippi pulp mill boiler was evaluated for potential use as an amendment to peat moss-based greenhouse substrates for production of young tomato plants. Between 0 and 50% ash was added to a custom-blended peat moss-based substrate, and these were compared to a commercially available substrate without ash. Addition of ash increased substrate pH, conductivity (EC), bulk density and water holding capacity, while reducing airspace and average particle size. In general, tomato plants grown in 0–40% ash had similar growth indexes as plants grown in commercial substrate. Increasing amounts of ash decreased tomato shoot nitrogen (N), potassium (K), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) concentration, and increased concentrations of phosphorus (P), calcium (Ca), sulfur (S), and boron (B). These results indicate that pulp mill ash has the potential to be used as a substrate component for greenhouse container production of tomato.