Effect of row spacing,growth stage,and nitrogen rate on spectral irradiance in winter wheat

Soil reflectance affects spectral irradiance measurements taken in winter wheat at early stages of growth when percent cover is low. The objective of this study was to determine the critical percent vegetation coverage needed for forage nitrogen (N) uptake calibration with indirect spectral irradiance measurements. Two field experiments were conducted at Tipton and Perkins, OK in October 1996. The effect of row spacing (15.2, 19.0, 25.4, and 30.5 cm) and growth stage (Feekes 4 and 5) under various N fertilizer rates (0, 56, 112, and 168 kg N ha^‐1) on spectral irradiance measurements from wheat was evaluated. The normalized difference vegetative index (NDVI) was used to characterize wheat canopy irradiance. In general, NDVI decreased with increasing row spacing and increased with N fertilizer rate at Feekes growth stage 4. Row spacing and N rate were independent of each other since no significant interaction was found. High correlation (r=0.81–0.98) was observed between NDVI and vegetation coverage. Percent vegetation coverage was a good predictor of the other dependent variables including forage dry matter, and total N uptake, which could indirectly be determined using NDVI. The coefficients of variation (CV's) from NDVI values decreased with increasing vegetation coverage suggesting that less variable NDVI values (CV less than 10%) might be obtained from plots where vegetation coverage exceeds 50%.     

Effect of growth stage and variety on spectral radiance in winter wheat

Before sensor‐based variable rate technology (VRT) can be used to reduce nitrogen (N) fertilizer rates in winter wheat (Triticum aestivum L.) spectral radiance readings must be understood. One prominent issue is the impact of crop growth stage on spectral radiance readings, and the ensuing problem of relating databases gathered at different locations and different stages of growth. In order to evaluate the impact of growth stage on spectral radiance, sensor readings were taken from a winter wheat variety trial and two long‐term N and phosphorus (P) fertility trials. The normalized difference vegetative index was computed using red and near infrared (NIR) spectral radiance measurements [NDVI=(NIR‐red)/(NIR+red)]. TotalNuptake in winter wheat at Feekes growth stages 4, 5, 7, and 8 was highly correlated with NDVI. In the variety trial, non‐significant differences in ND VI readings were noticed between the five common genotypes (by growth stage) grown in this region. However, slopes from linear regression of total N uptake on NDVI were different at different stages of growth, which suggests the need for growth stage specific calibration. Freeze injury (altered tissue color) affected the relationship between total N uptake and NDVI, however, NDVI continued to be a good predictor of in‐season total N uptake in wheat even though cell blasting altered tissue color. This work showed that NDVI is a good predictor of biomass, but not necessarily total N concentration in plant tissue. The amount of variability in total N uptake as explained by NDVI increased with advancing growth stage (Feekes 4 to 7), largely due to an increased percentage of soil covered by vegetation.     

Long-term cattle manure application in soil

Studies were conducted to investigate the effects of long-term management practices on level and distribution of soil P and enzyme activities involved in P transformations in soil. Treatments included manure, P, NP, NPK, and NPK plus lime. Cattle manure was applied every 4 years at 269 kg N ha^-1 for over a century and chemical fertilizers were applied every year at 67 kg N, 14.6 kg P, and 28 kg K ha^-1 for over 69 years. Total soil P increase in soils ranged from 4.5 to 10.3 kg P ha^-1 year^-1 with the highest increase detected in the P-treated and the lowest in the manure-treated plot. Approximately 77-86% of the applied inorganic fertilizer-P in the past 69-71 years was recovered either in the harvested grain or remained in the top 30 cm of soil, while only 32% of the applied manure-P was recovered. Microbial biomass C and activities of alkaline phosphomonoesterase, phosphodiesterase, inorganic pyrophosphatase, and dehydrogenase were significantly higher in the soil treated with cattle manure. Acid phosphomonoesterase activity, however, was significantly higher in soils treated with chemical fertilizers. Results from this study suggested that manure-P is relatively more mobile than inorganic fertilizer-P. Long-term application of cattle manure promoted microbiological activities and P cycling, but did not result in P accumulation to levels close to those in inorganic P fertilizer-treated soils.     

Use of spectral radiance for correcting nitrogen deficiencies and estimating soil test variability in an established bermudagrass pasture

The use of variable rate technology has become increasingly popular for applying plant nutrient elements. The most widely used method for determining variable fertilizer rates is presently based on soil testing and yield mapping. Three field studies (Bumeyville 1995, Burneyville 1996, and Ardmore 1996) were initiated in established Midland bermudagrass [Cynodon dacrylon (L) Pers.] pastures to determine the relationship between spectral radiance at specific wavelengths with forage nitrogen (N) removal and biomass, and to determine field variability of soil test parameters. Variable N (applied to 1.5 × 2.4 m subplots within 2.4 × 45.7 m main plots), fixed N and check treatments were evaluated at each location. Spectral radiance readings were taken in the red (671±6 nm), green (570±6 nm), and near infrared (NIR) (780±6 nm) wavelengths. The normalized difference vegetation index (NDVI) was calculated as NIR‐red/NIR+red. Variable N rates were applied based on NDVI. The highest fixed variable N rate was set at 224, 336, and 672 kg N ha^‐1 for Burneyville, 1995, 1996, and Ardmore, 1996, respectively. At Bumeyville, soil samples were collected in all variable rate plots (1.5 × 2.4 m) and analyzed for various soil test characteristics. NDVI, red, green, and NIR spectral radiance readings were correlated with bermudagrass forage N removal and yield. Correlation of forage yield and N removal with red, NIR, and NDVI were best with maximum forage production, however, when forage production levels were low correlation decreased dramatically for the red wavelength compared with NIR and NDVI. Forage yield and forage N removal in variable rate treatments increased when compared to the check while being equal to the half‐fixed and fixed rates where higher N rates were applied. Also, variability about the mean in variable rate plots was significantly lower than half‐fixed and fixed rates which supports adjusting N rates based on indirect NDVI measurements. Variable N rate plots reduced fertilizer inputs by 60% and produced the same yield as fixed rate plots, while fixed and half‐fixed rates did not increase N content in the forage over that of the variable rate treatment. Soil sample data collected from small consecutive plots (<4 m²) was extremely variable indicating that intense sampling would be needed if variable fertilizer application were to be based on soil test results.     

Supplementation with sunflower seeds in beef cattle did not impact on oocyte and in vitro embryo production

Supplementation with compounds rich in linoleic acid, including sunflower seed supplementation, promotes increase in conception rates in cows. We aimed to evaluate whether the sunflower seed (linoleic acid source) supplementation in beef donor females alters the plasma concentrations of cholesterol, triglycerides, HDL and LDL, increases the number and quality of oocytes, increases the cleavage rates and determines an improvement in number and quality of in vitro produced blastocysts. Thus, Nelore females were divided into two groups of 15 animals to receive supplementation with or without sunflower seed for 57 days. Females underwent follicular aspiration and the oocytes were subjected to in vitro embryo production. There was no difference (p > .1) between control group and group supplemented with sunflower seed on the number of displayed follicles; number of aspired oocytes; recovery rate; cleavage rate; number of embryos; number of blastocysts; embryos number of grades I and II; plasma concentrations of total cholesterol, triglycerides; HDL and LDL. Therefore, sunflower seed supplementation in oocyte donors did not increase the number and quality of oocytes, cleavage rates and the number and quality of blastocysts produced in vitro.     

Cellular Composition and Viability of Cloned Bovine Embryos Using Exogene-Transfected Somatic Cells

The present study compared the efficiency of transgenic (TG) cloned embryo production by somatic cell nuclear transfer (SCNT) with fetal-derived fibroblast cells (FFCs) which were transfected with pEGFP-N1 to in vitro-fertilized (IVF), parthenogenetic and SCNT counterparts by evaluating the rates of cleavage and blastocyst formation, apoptosis rate at different developmental stages, cell number, ploidy and gene expression in blastocysts. In SCNT and TG embryos, the rates of cleavage and blastocyst formation were significantly lower (p < 0.05) than those of IVF controls, but it did not differ between SCNT and TG embryos. In IVF control, 86.7% embryos displayed diploid chromosomal complements and the rates were significantly (p < 0.05) higher than those of SCNT and TG embryos. Most TG embryos (79%) with FFCs expressed the gene by both PCR and under fluorescence microscopy. The expression of apoptosis by TUNEL was first detected at six to eight cell stages in all embryos of IVF, SCNT and TG groups, but the expression rate at each developmental stages was significantly higher (p < 0.05) in SCNT and TG embryos than in IVF counterparts. The expression rate in inner cell mass (ICM) of TG embryos was significantly higher (p < 0.05) than in SCNT and IVF embryos. These results indicate that the high occurrence of apoptosis observed in SCNT and TG embryos compared with IVF counterparts might influence the developmental competence. Moreover, the SCNT embryos derived using non-transfected donor cells exhibited a lower apoptosis expression in ICM cells than in TG embryos derived using pEGP-N1-transfected donor cells suggesting a possible role of negative gene effect in TG embryos.