Effects of Method and Level of Nitrogen Fertilizer Application on Soil pH, Electrical Conductivity, and Availability of Ammonium and Nitrate in Blueberry

Blueberries (Vaccinium spp.) require low soil pH and prefer N primarily as ammonium for optimum production. Nitrogen fertilizer methods and rates were evaluated in a new field of `Bluecrop" blueberry (Vaccinium corymbosum L.) to determine their effects on soil pH and availability of ammonium and nitrate in soil solution. Treatments included four application methods (split fertigation, continuous fertigation, and two non-fertigated controls) and four rates of N application (0, 50, 100, and 150 kg/ha N). Fertigation treatments were irrigated by drip and injected with liquid urea fertilizer; split fertigation was applied as a triple-split from April to June while continuous fertigation was applied weekly from leaf emergence to approximately 2 months prior to the end of the growing season. Non-fertigated controls were fertilized with a triple-split of granular ammonium sulfate and irrigated by drip or microsprays. Soil pH was usually lower with microsprays than with drip, even when no N fertilizer was applied; however, soil pH was also reduced with higher N applications and, in fact, was similar between continuous fertigation and granular fertilizer (microspray) treatments when 150 kg/ha N was added. Nitrogen application with granular fertilizer, whether irrigated by microspray or drip, maintained much higher ammonium concentrations than continuous or split fertigation but often increased electrical conductivity (salinity) of the soil solution (ECw) to >2 dS/m. By comparison, ECw was always <1.5 dS/m with either fertigation method. Granular N application coupled with microsprays also resulted in higher nitrate concentrations than any other treatment, which may lead to more N leaching since the ability of blueberry to acquire nitrate-N is limited

Patterns of wood carbon dioxide efflux across a 2,000-m elevation transect in an Andean moist forest

During a 1-year measurement period, we recorded the CO2 efflux from stems (RS) and coarse woody roots (RR) of 13–20 common tree species at three study sites at 1,050, 1,890 and 3,050 m a.s.l. in an Andean moist forest. The objective of this work was to study elevation changes of woody tissue CO2 efflux and the relationship to climate variation, site characteristics and growth. Furthermore, we aim to provide insights into important respiration–productivity relationships of a little studied tropical vegetation type. We expected RS and RR to vary with dry and humid season conditions. We further expected RS to vary more than RR due to a more stable soil than air temperature regime. Seasonal variation in woody tissue CO2 efflux was indeed mainly attributable to stems. At the same time, temperature played only a small role in triggering variations in RS. At stand level, the ratio of C release (g C m−2 ground area year−1) between stems and roots varied from 4:1 at 1,050 m to 1:1 at 3,050 m, indicating the increasing prevalence of root activity at high elevations. The fraction of growth respiration from total respiration varied between 10 (3,050 m) and 14% (1,050 m) for stems and between 5 (1,050 m) and 30% (3,050 m) for roots. Our results show that respiratory activity and hence productivity is not driven by low temperatures towards higher elevations in this tropical montane forest. We suggest that future studies should examine the limitation of carbohydrate supply from leaves as a driver for the changes in respiratory activity with elevation

Effects of Salinity Induced by Ammonium Sulfate Fertilizer on Root and Shoot Growth of Highbush Blueberry

Abstract Ammonium sulfate fertilizer is commonly used in highbush blueberry (Vaccinium corymbosum L.), but due to a high salt index, it often causes salt damage, particularly in young plants, when too much of the fertilizer is applied. A study was done to determine the sensitivity of blueberry to ammonium sulfate and identify the salinity threshold in which plant growth is affected by the fertilizer. One-year-old ‘Bluecrop’ blueberry plants were transplanted from 0.5-L pots to 8-L pots filled with a 1:1 (v/v) mixture of peat and pine bark and fertilized with four rates of 0, 0.25, 0.75, and 1.5 g•L-1 ammonium sulfate solution. Each solution was applied 2-3 times per week as needed for a total of 8 weeks. Electrical conductivity of the solutions (ECw) increased linearly with fertilizer rate and averaged 0.1, 0.5, 1.5, and 3.0 dS•m-1, respectively. Fertilizer rate had no effect on total shoot dry weight but significantly affected new root dry weight and partitioning of shoot biomass. Plants fertilized with 1.5 g•L-1 ammonium sulfate produced less roots and had a lower leaf to stem dry weight ratio than those fertilized with 0 or 0.25 g•L-1, which indicates that root and leaf growth in blueberry was sensitive to ECw between 1.5 and 3.0 dS•m-1. In the field, fertilizer programs and practices (e.g., fertigation) that maintain ECw in soil solution < 1.5 dS•m-1 are recommended for rapid establishment of highbush blueberry

Potential of Elemental Sulfur Fertigation to Reduce High Soil pH for Production of Highbush Blueberry

Abstract Blueberry is adapted to acidic soil conditions but is often planted in high pH soils by adding elemental sulfur (So) prior to planting. Two pot experiments were carried out in a glasshouse to determine the potential of applying Sº by fertigation through a drip irrigation system. In the first experiment, So was applied at four rates of 0, 0.36, 0.72, and 1.44 g per application to 4-L pots filled with one of three different soil textures [1:0, 1:1, and 1:2 sandy loam soil:sand (v/v)]. In the second experiment, So was applied at three rates of 0, 0.36, 0.72 g per application to 4- and 16-L pots filled with soil only. Pots were irrigated using a 2.3 L•h-1 pressure-compensating drip emitter located in the center of each pot. Micronized water-dispersible Sº granules were dissolved in water and injected through the drip system twice a week for 4 weeks in each experiment. Soil leachate pH decreased from 6.5 to 4.2 within 19 days after So was first applied in the first experiment, but pH was not affected by soil texture or the amount of So applied and decreased only 0.2 units by additional So applications made between 19 and 33 days. Soil and soil leachate pH likewise decreased from 7.3 to 4.5 in the second experiment, but in this case, pH took up to 10 days longer to decline in the 14-L pots than in the 4-L pots. Soil pH in the larger pots was also lower at 0-5 cm depth than at 5-10 cm depth and lower on the edge of the wetting front than directly under the drip emitter. The results indicate that So fertigation is an effective method for quickly reducing soil pH with much less So than conventional application and warrants further investigation in the field

Nitrogen Requirements at Bulb Initiation for Production of Intermediate-Day Onion in a Mediterranean Climate

Abstract The effect of nitrogen application on growth, nitrogen (N) uptake, yield, and quality of intermediate-day onion (Allium cepa L. ‘Guimar’) was evaluated in the field in southern Portugal. Plants were fertilized with 30 kg•ha-1 N at transplanting, 10 kg•ha-1 N at 29 days after transplanting (DAT) during early leaf growth, and with 0, 20, 40, and 60 kg•ha-1 N at 51 DAT at the initiation of bulbing. The root system of plants in each treatment were concentrated in the top 0.1 m of soil and limited to 0.3-m depth but neither root length density nor rooting depth were affected by N application during later stages of bulb development. Leaf and bulb dry matter, on the other hand, increased linearly with N rate during bulb growth (85 DAT) and at harvest (114 DAT), respectively. Soil nitrate-N (NO3-N) at 0-0.3 m depth likewise increased linearly with N rate during bulb growth but declined from 15−30 mg•kg-1 at bulbing to <10 mg•kg-1 in each treatment by harvest. A substantial amount of N in the plants, which ranged from 302−525 mg, was taken up from the soil. Application of 60 kg/ha N resulted in luxury consumption. Yield (fresh bulb weight) was correlated to bulb diameter and averaged 0.19 kg/plant with no N at bulbing and increased to as much as 0.28 kg/plant with 60 kg•ha-1 N. Bulbs harvested from plants fertilized 40−60 kg/ha N averaged 8.2−8.5 cm in diameter, while those from plants with no N at bulbing averaged only 7.2 cm in diameter. Other components of quality, including neck diameter, bulb water content, soluble solids, and juice pH, were not affect by N applied at bulbing. Application of N fertilizer is thus recommended at bulbing to increase N uptake and production without any impact on quality of intermediate-day onions, particularly in dry Mediterranean climates where many onions are produce