D. V. Calvert

Nitrogen mineralization and transformation from composts and biosolids during field incubation in a sandy soil.

Field evaluation of nutrient release from composts is important to estimate nutrient contribution to crops, potential leaching of nutrients, and, ultimately, to determine optimum application rates, timing, and placement of composts. Field incubation and laboratory analyses were conducted to evaluate

AMMONIA VOLATILIZATION FROM DIFFERENT FERTILIZER SOURCES AND EFFECTS OF TEMPERATURE AND SOIL pH1

Improved understanding of nitrogen sources, environmental factors, and nitrification effects on NH 3 volatilization is needed for optimal management of nitrogen in crop production systems. In the laboratory, a sponge-trapping and KCl-extraction method was modified for measuring NH 3 volatilization from different N sources as affected by temperature and soil pH. The kinetics of NH 3 volatilization from four N sources surface applied to an Alfisol (a Riviera fine sand, pH 7.9) followed an initial rapid reaction, and then a slow reaction, which was adequately described by a Langmuir kinetic model. The potential maximum NH 3 volatilization (q m ) under the experimental conditions, as predicted by the Langmuir equation, decreased in the order: NH 4 HCO 3 (23.2% of applied NH 4 -N) > (NH 4 ) 2 SO 4 (21.7%) > CO(NH 2 ) 2 (21.4%) > NH 4 NO 3 (17.6%). With an increase in NH 4 -N application rate, NH 3 volatilization increased significantly for (NH 4 ) 2 SO 4 , CO(NH 2 ) 2 , and NH 4 HCO 3 but decreased for NH 4 NO 3 . Ammonia volatilization was minimal at the initial soil pH of 3.5 and increased rapidly with increasing pH up to 8.5. The potential maximum NH 3 volatilization increased by 2- and 3-fold, respectively, with an increase in the incubation temperature from 5 to 25 °C, and from 25 to 45 °C, respectively. The greatly enhanced NH 3 volatilization at 45 °C, compared with that at 25 °C, was related to the inhibition of nitrification at the high temperature, which increased the availability of NH 4 for NH 3 volatilization over a prolonged period of time.

Clinoptilolite zeolite and cellulose amendments to reduce ammonia volatilization in a calcareous sandy soil

Leaching of nitrate (NO3−) below the root zone and gaseous losses of nitrogen (N) such as ammonia (NH3) volatilization, are major mechanisms of N loss from agricultural soils. New techniques to minimize such losses are needed to maximize N uptake efficiency and minimize production costs and the risk of potential N contamination of ground and surface waters. The effects of cellulose (C), clinoptilolite zeolite (CZ), or a combination of both (C+CZ) on NH3 volatilization and N transformation in a calcareous Riviera fine sand (loamy, siliceous, hyperthermic, Arenic Glossaqualf) from a citrus grove were investigated in a laboratory incubation study. Ammonia volatilization from NH4NO3 (AN), (NH4)2SO4(AS), and urea (U) applied at 200 mg N kg−1 soil decreased by 2.5-, 2.1- and 0.9-fold, respectively, with cellulose application at 15 g kg−1 and by 4.4-, 2.9- and 3.0-fold, respectively, with CZ application at 15 g kg−1 as compared with that from the respective sources without the amendments. Application of cellulose plus CZ (each at 15 g kg−1) was the most effective in decreasing NH3 volatilization. Application of cellulose increased the microbial biomass, which was responsible for immobilization of N, and thus decreased volatilization loss of NH3–N. The effect of CZ, on the other hand, may be due to increased retention of NH4 in the ion-exchange sites. The positive effect of interaction between cellulose and CZ amendment on microbial biomass was probably due to improved nutrient retention and availability to microorganisms in the soil. Thus, the amendments provide favorable conditions for microbial growth. These results indicate that soil amendment of CZ or CZ plus organic materials such as cellulose has great potential in reducing fertilizer N loss in sandy soils.

Chemical Association Of Cu, Zn, Mn, And Pb In Selected Sandy Citrus Soils

Distribution of various forms of copper, zinc, manganese and lead in the surface horizon and the distribution of total metal concentrations in different soil horizons down to 150 cm depth in six soil series (representing Spodosols, Alfisols, and Entisols) under citrus production were investigated

Microbiological and Biochemical Indexing Systems for Assessing Quality of Acid Soils

Acid soils play an important role in the production of world food and fiber. The majority of acid soils in the tropical and subtropical regions are highly weathered, subject to intensive cropping, and vulnerable to soil erosion. Degradation of these soils poses a great challenge to sustainable agriculture in these regions. An efficient indexing system using minimal physical, chemical, and biological parameters is immediately needed to assess and monitor the dynamics of soil quality under diversified farming systems and to improve agricultural practices and productivity. Various physical, chemical, and biological properties can be used to characterize soil quality. However, the number, activity, and diversity of microorganisms and the related biochemical processes are the most important components of soil quality, especially for the highly weathered acid soils, in which plant productivity is closely related to biological cycling. Several microbiological and biochemical parameters have been suggested as indicators of soil quality. They include: microbial biomass carbon (Cmic), nitrogen (Nmic), and phosphorus (Pmic) and their turnover rates; the microbial quotient (MQ) (Cmic/organic C ratio); basal respiration (qCO2); the microbial metabolic quotient (MMQ) (qCO2/Cmic); the ratio of microbial N over total Kjeldahl N; and enzyme activity. Recently, microbial diversity parameters such as community level physiological profile, phospholipid fatty acids, the ratio of Gram-negative/Gram-positive bacteria, the ratio of fungal/bacterial microorganisms, and free-living diazotrophic bacteria, etc., have been identified as important indicators of soil quality. All these microbiological and biochemical parameters have been shown to relate to soil productivity and respond to changes of land use, vegetation coverage, agricultural practices such as liming, fertilization, and tillage, as well as climate factors (temperature and rainfall). Current progress on measurement, interpretation, and potential application of the microbiological and biochemical indices in assessing quality, fertility, and sustainability of highly weathered acid soils are reviewed in this chapter.

Root distribution of grapefruit trees under dry granular broadcast vs. fertigation method

The aim of this study was to determine the effects of nitrogen (N) fertilization methods on root distribution and mineral element concentrations of White Marsh grapefruit (Citrus paradisi MacFadyen) trees on sour orange (C. aurantium Lush) rootstock on a poorly drained soil. At 0–15 cm depth of soil, root density was significantly greater for trees receiving 112 kg N ha-1 yr-1 as dry granular broadcast than those receiving the same amount of N as fertigation. Of the total roots in the top 60 cm soil, >75% was at 0–15 cm and <10% was at 30–60 cm. Root density was greatest near the emitter. Nitrogen concentration of roots was greater for the trees which received fertigation as compared to the trees which received dry fertilizer broadcast or no N.

Leaching of Nitrate, Ammonium, and Phosphate From Compost Amended Soil Columns

Compost amendment to agricultural soils has been reported to reduce disease incidence, conserve soil moisture, control weeds, or improve soil fertility. Application rate and placement of compost largely depends on the proposed beneficial effects and the rate may vary from 25 to 250 Mg ha−1 (N content up to 4 percent). Application of high rates of compost with high N or P levels may result in excessive leaching of nitrate, ammonium, and phosphate into the groundwater. Leaching could be a serious concern on the east coast of Florida with its inherent high annual rainfall, sandy soils and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were applied on the surface of an Oldsmar sand soil (in 7.5 cm diameter leaching columns) at 100 Mg ha−1 rate and leached with deionized water (300 ml day−1, for five days; equivalent to 34 cm rainfall). The concentrations of NO3-N, NH4-N, and PO4-P in leachate reached as high as 246, 29,...

Uptake and Accumulation of Cadmium and Zinc by Sedum Alfredii Hance at Different Cd/Zn Supply Levels

Abstract Sedum alfredii Hance has been identified to be a zinc (Zn) hyperaccumulating plant species native to China. In this study, growth responses, uptake and accumulation of cadmium (Cd) and Zn by S. alfredii were examined at Cd/Zn combining supply levels. The results showed that optimal growth for both shoots and roots was found when the plant grew at the Cd/Zn level of 100/500 μmol L−1. The concentrations of Cd and Zn in leaves and Sstems of Sedum afredii H increased with increasing Cd and Zn supply levels. The distributions of the metals in different plant parts decreased in the order: stem > leaf ≫ root for Zn and leaf > stem ≫ root for Cd. The highest concentrations of Zn (23.2 mg g−1) in the stems and Cd (12.1 mg g−1) in the leaves were noticed when the plants were grown at the Zn/Cd levels of 1000/50 and 500/400 μmol L−1, respectively. The maximum Cd and Zn accumulations in the shoots were 5.1 and 11.2 mg plant−1 at the Cd/ Zn combining levels of 400/250 and 100/500 μmol L−1, respectively. Zinc supply levels <500 μmol L−1 enhanced Cd concentrations in stems and leaves at the Cd levels <100 μmol L−1 and Cd concentration in roots at the Cd levels <50 μmol L−1. Cadmium at the supply levels ≥100 μmol L−1 decreased considerably root Zn concentrations for all the Zn levels, slightly increased leaf Zn concentrations at the Zn levels ≥250 μmol L−1, but had minimal effect on leaf Zn concentrations at the Zn levels ≥500 μmol L−1. The results indicate that S. Alfredii has an extraordinary ability to co-tolerate Cd/Zn toxicities, and to absorb and hyper-accumulate Cd and Zn under a range of Cd/Zn combining levels. Zinc addition at relatively low levels could stimulate Cd uptake and translocation, whereas Cd supply enhanced Zn translocation and partition to the shoots. Sedum alfredii is a Zn/Cd hyperaccumulator, which can be a valuable material for further study on the mechanisms of metal uptake and accumulation and for phytoremediation of the soils with Zn/Cd combined contamination.

ASSESSING COPPER THRESHOLDS FOR PHYTOTOXICITY AND POTENTIAL DIETARY TOXICITY IN SELECTED VEGETABLE CROPS

Copper pollution in soils is widespread, and its accumulation in crop products could pose a risk on human health. In this paper, bioavailability of added copper (Cu) and critical Cu concentrations in a vegetable garden soil was evaluated for Chinese cabbage (Brassica chinensis L.), pakchoi (Brassica chinensis L.), and celery (Apiumg graveolens L. var. dulce DC) based on human dietary toxicity. The availability of added Cu in the soil decreased with incubation time, and had minimal change after 10–12 weeks. After incubated for 12 weeks, about 60% of added Cu was not extractable by DTPA. The same crops were also grown in sand culture to determine their responses to solution Cu. Shoot growth was significantly inhibited at Cu concentrations above 10 mg kg−1 in the solution or above 150 mg kg−1 (DTPA-Cu) in the soil. The sensitivity of the crops to Cu toxicity differed among the three vegetable crops. Copper concentration in shoots and edible parts varied with Cu supply levels and type of the vegetables. Negative correlations (r=−0.90–0.99**) were noted between Cu concentration in shoots and fresh matter yields, but Cu concentrations in the edible parts were positively correlated with available and total Cu in the soil (r=0.91–0.99**). The critical tissue Cu concentrations at 10% shoot DM reduction were 19.4, 5.5, 30.9 mg kg−1 for Chinese cabbage, pakchoi, and celery, respectively. Based on the threshold of human dietary toxicity for Cu (10 mg kg−1), the critical concentrations of total and available Cu in the soil were 430 and 269 mg kg−1 for pakchoi, 608 and 313 mg kg−1 for celery, and 835 and 339 mg kg−1 for Chinese cabbage, respectively.

Effects of nitrogen fertilization of grapefruit trees on soil acidification and nutrient availability in a Riviera fine sand

Nitrogen (N) fertilizer applied in the NH4+ form results in some degree of soil acidification, which could influence nutrient availability to plants and nutrient losses through leaching. Effects of various N rates (0 – 168 kg N ha-1 yr-1) on soil acidification and nutrient availability were investigated in a Riviera fine sand with 26-year-old white Marsh grapefruit (Citrus paradisi MacFadyen) trees. Soil pH significantly decreased with increasing NH4–N rates. Application of 112 kg N ha-1 yr-1 for four years decreased the pH by 0.7 to 1.7 unit. Soil acidification was greater when the NH4+ form of N fertilizer was applied as dry soluble granular material compared to fertigation or controlled release forms. The marked effect of NH4–N fertilization on the pH of the Riviera fine sand was due to its low buffering capacity. Soil acidification increased the concentration of extractable Fe and P but decreased that of K, Zn and Mn. Soil pH was positively correlated with concentration of Ca, but negatively with concentrations of Fe, Mn and Zn in six-month-old spring flush leaves of the grapefruit trees. Leaf P concentrations, however, were poorly correlated with soil pH. This study also demonstrated an increase in leaching of P and K below the grapefruit trees rootzone with a decrease in soil pH.