C. W. Wood

Field chlorophyll measurements for evaluation of corn nitrogen status 1

Abstract An experiment was conducted on Norfolk sandy loam soil (Fine‐loamy, siliceous, thermic Typic Kandiudults) during two years to determine the feasibility of using field chlorophyll measurements for evaluation of corn (Zea mays L.) N status. Nitrogen was applied at rates of 56, 112, 168, 224, 280 and 336 kg ha‐1 to establish a range of corn chlorophyll levels, tissue N concentrations, and grain yields. At the V10 and midsilk stages of growth, field chlorophyll measurements were taken with a hand‐held chlorophyll meter (SPAD‐502 Chlorophyll Meter, Minolta Camera Co., Ltd., Japan)3 and tissue N was determined. A typical curvilinear grain yield response to N fertilizer was observed both years; maximum agronomic yields were obtained with 227 and 242 kg N ha1, respectively, in 1990 and 1991. Tissue N concentrations at V10 and midsiik were a good predictor of grain yield. Field chlorophyll measurements were highly correlated with tissue N concentrations at both growth stages during both years of the study...

Effects of soil compaction and water-filled pore space on soil microbial activity and N losses

Abstract Soil compaction is a significant production problem for agriculture because of its negative impact on plant growth, which in many cases has been attributed to changes in soil N transformations. A laboratory experiment was conducted to study the effect of soil compaction and water‐filled pore space on soil microbial activity and N losses. A hydraulic soil compaction device was used to evenly compress a Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Kandiudults) soil into 50 mm diameter by 127 mm long cores. A factorial arrangement of three bulk density levels (1.4, 1.6, and 1.8 Mg/m3) and four water‐filled pore space levels (60, 65, 70, 75%) was used. Fertilizer application of 168 kg N/ha was made as 1.0 atom % 15N as NH4NO3. Soil cores were incubated at 25°C for 21 d. Microbial activity decreased with both increasing water‐filled pore space and soil bulk density as measured by CO2‐C entrapment. Nitrogen loss increased with increasing bulk density from 92.8 to 334.4 g N/m3 soil at 60% wa...

Nitrogen transformations and balance in channel catfish ponds.

A nitrogen (N) budget was developed for four, 400-m 2 ponds stocked with 550 channel catfish (Ictalurus punctatus) fingerlings that were fed to satiation daily for 133 days with a ration containing 4.85% N. Feed accounted for 87.9% of the N input to ponds. Abundant N from ammonia (NH3), ammonium (NH4 ), and nitrate (NO3 ) and the high total N: total phosphorus ratio in pond waters prevented appreciable biological N2 fixation. There were four main N losses: fish harvest (31.5%); denitrification (17.4%); NH3 volatilization (12.5%); accumulation in bottom soils (22.6%). Nitrification averaged 70 mg N m 2 d 1 , denitrification averaged 38 mg N m 2 d 1 , and phytoplankton removed NO3 Na t 24 mg Nm 2 d 1 . Mineralization of feed N to NH3 averaged 59 mg N m 2 d 1 . As feed is the largest N input in catfish ponds, improved feeds and feeding practices can increase the proportion of N recovered in fish and reduce the amount of NH3 excreted by fish. Efficient aeration and water circulation also should enhance nitrification and oxidation of organic N.

Determination of wheat nitrogen status with a hand‐held chlorophyll meter: Influence of management practices 1

Abstract The nitrogen (N) status of wheat at specific growth stages has potential in predicting yield goals and supplemental N fertilizer requirements but there is a need for a simple and reliable method for field determination of wheat (Triticum aestivum L.) N status under different management schemes. This field study was conducted for two seasons (1989–90 and 1990–91) on a Norfolk sl (fine‐loamy, siliceous thermic Typic Kandiudults) in east‐central Alabama. Treatment variables were tillage, fungicide and N rate. Tillage treatments were disk/harrow or paraplow. Fungicide treatments were no fungicide or propiconazole (Tilt®) applied at Feekes growth stage (GS) 8. Nitrogen rates were a 0‐N control and 45, 90, 134, or 179 kg N/ha applied in a two‐way split with 22.5 kg N/ha applied at planting and the remainder applied in mid‐February. Whole plant samples at GS 3 and 5, and flag leaf samples at GS 10.51 were analyzed for N; a hand‐held meter was used to measure chlorophyll concentrations at these sampling ...

Determination of cotton nitrogen status with a handheld chlorophyll meter

Abstract The ability of a hand‐held chlorophyll meter (SPAD‐502 Chlorophyll Meter3, Minolta Camera Co., Ltd., Japan) to determine the N status of cotton (Gossypium hirsutum L.) was studied at field sites in Alabama and Missouri. Meter readings on the uppermost fully‐expanded leaf were compared to leaf‐blade N and petiole NO3‐N at first square, first bloom and midbloom as to their seed cotton yield predictive capability. Nitrogen was applied at rates of 0, 45, 90, 135, 180 and 225 kg ha‐1 to establish a range of cotton chlorophyll levels, tissue N concentrations, and seed cotton yields. A typical curvilinear cotton yield response to N fertilizer was observed in Alabama experiments. Because of adverse weather conditions, cotton yield in Missouri experiments did not respond to N. Chlorophyll meter readings were significantly correlated to leaf‐blade N concentration at all three stages of growth for all experiments. In Alabama, chlorophyll meter readings compared favorably to leaf‐blade N and petiole NO3‐N wi...

Free-air CO2 enrichment effects on soil carbon and nitrogen

Since the onset of the industrial revolution, atmospheric CO2 concentration has increased exponentially to the current 370 #mol mo1-1 level, and continued increases are expected. Previous research has demonstrated that elevated atmospheric CO2 results in larger plants returning greater amounts of C to the soil. However, the effects of elevated CO 2 on C and N cycling and long-term storage of C in soil have not been examined. Soil samples (in 0-50, 50100, and 100-200 mm depth increments) were collected after 3 years of cotton (Gossypium hirsutum L.) production under free-air CO 2 enrichment (FACE, at 550 #tool CO 2 mol-l), in combination with 2 years of different soil moisture regimes (wet, 100% of evapotranspiration replaced, or dry, 75% and 67% of evapotranspiration replaced in 1990 and 1991, respectively) on a Trix clay loam (fine, loamy, mixed (calcareous), hyperthermic Typic Torrifluvent) at Maricopa, Arizona. Ambient plots (370 #mol CO2 mol -I (control)), in combination with the wet and dry soil moisture regimes, were also included in the study. Soil organic C and N concentrations, potential C and N mineralization, and C turnover were measured. Increased input of cotton plant residues under FACE resulted in treatment differences and trends toward increased organic C in all three soil depths. During the first 30 days of laboratory incubation, available N apparently limited potential C mineralization and C turnover in all treatments. Between 30 and 60 days of incubation, soils from FACE plots had greater potential C mineralization with both water regimes, but C turnover increased in soils from the dry treatment and decreased in soils where cotton was not water stressed. These data indicate that in high-CO 2 environments without water stress, increased C storage in soil is likely, but it is less likely where water stress is a factor. More research is needed before the ability of soil to store additional C in a high-CO 2 world can be determined.

Agroecosystem management effects on soil carbon and nitrogen

The cumulative effects of long-term (1980–1990) tillage and crop rotation management on soil organic C and N concentrations and potential mineralization were determined. Tillage systems studied were conventional moldboard plow tillage and conservation tillage, with various crop rotations including: continuous soybean (Glycine max L.)-wheat (Triticum aestivum L.) cover (SW); continuous corn (Zea mays L.)-wheat cover (CW); and corn-wheat cover-soybean-wheat cover (CWSW). Surface soil (0–5, 5–10, and 10–20 cm depth increments) organic C and N concentrations and potential mineralization were determined for all tillage/rotation combinations in October 1990. After 10 years, surface soil organic C and N concentrations were 67% and 66% higher, respectively, under conservation tillage than plow tillage to a depth of 10 cm. Potential C and N mineralization followed a pattern similar to organic C and N distribution. However, differences in substrate quality below 10 cm indicated that conservation tillage promoted N immobilization. Crop rotation had less effect than tillage on soil organic C and N amounts and potential mineralization. Rotations with higher frequency of corn (CW and CWSW) had higher organic C and N concentrations and C mineralization than SW; crop rotation had no effect on potential N mineralization. Tillage system apparently influenced soil organic matter concentrations and mineralization via crop residue incorporation rather than any effects owing to concentration differences at the soil surface, while the effect of crop rotation was related to amount of crop residues added between 1980 and 1990.

Impact of row spacing, nitrogen rate, and time on carbon partitioning of switchgrass

Cultivation of switchgrass (Panicum virgatum L.) as an energy crop could lower atmospheric carbon dioxide (CO2) levels by replacing fossil fuel and sequestering carbon (C). Information on the details of C partitioning within the switchgrass–soil system is important in order to quantify how much C is sequestered in switchgrass shoots, roots, and soil. No studies of C partitioning in a switchgrass–soil system under field conditions have been conducted. This study was aimed at determining the impact of agricultural management practices, such as row spacing and nitrogen (N) application rate, on C partitioning within the switchgrass–soil system; changes in C partitioning with time after switchgrass establishment were also considered. The results indicate that C storage in switchgrass shoots was higher with wide than narrow rows, and increased with N application rates. These responses were due to higher yields with wide than narrow rows and higher yields as N application rate increased. Carbon storage in shoots was 14.4% higher with 80-cm than 20-cm row spacing. Annual application of increased C storage in shoots by 207% and 27% when compared with annual applications of 0 and , respectively. Carbon storage increased by 62% over time from 1995 to 1996 in newly established switchgrass on sandy loam soil in the coastal plain of Alabama. Rate of C increase in roots (72%) was higher than in shoots (49%) between 1995 and 1996. Carbon storage was in order of soil C > root C > shoot C in both 1995 and 1996. The root/shoot ratio of C storage was 2.2. It appears that C partitioning to roots plays an important role in C sequestration by switchgrass.

Storage and handling characteristics of pellets from poultry litter

Poultry litter (combination of accumulated manure and bedding materials) was pelleted through a 3/16-in. (4.76-mm) diameter die. The storage and handling properties of the pellets were measured within a moisture range of 6.0% and 22.0% (w.b.). Bulk density and particle density of the pelleted litter respectively decreased and increased with increase in moisture content. The force required to rupture the pellets varied from 316 N at 6.0% moisture content to 68 N at 22.0% w.b. Durability of the pellets were also affected by moisture content. Pellet moisture absorption rates were significantly (P < 0.05) affected by air relative humidity. The values of thermal conductivity, thermal diffusivity and specific heat for the pellets were respectively obtained to be 0.264W/m K, 2.67 . 10-7 m2/s, and 1265.6 J/kg K.

Nutrient accumulation and nitrate leaching under broiler litter amended corn fields

Abstract Alabamas broiler chicken (Gallus gallus) industry produces large amounts of waste, which are disposed of by application to crop and pasture land. Land application of litter (manure and bedding) from broiler production can lead to contamination from losses of nutrients accumulated in soil. A study was conducted on 2 and 4% slopes from 1991 to 1993 at Belle Mina, Alabama, to determine the effects of broiler litter (BL) on soil elemental concentrations and nitrate leaching under a corn (Zea mays L.) ‐ winter rye (Secale cereale L.) cropping system amended with either: l) 9 mg#lbha‐1 of BL, 2) 18 mg#lbha‐1 of BL, or 3) commercial fertilizer (F) at a recommended rate. Soil was sampled to 100 cm prior to corn planting and subsequent to com harvest. Soil leachate samples were collected biweekly with wick lysimeters installed at a depth of 100 cm. Litter applications increased concentrations of soil organic carbon (C), extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu) ...