Nitrogen utilization by corn (Zea mays L.) is influenced by the form of inorganic N present in the root zone. A field experiment was conducted on Enon sandy loam (fine, mixed, thermic Ultic Hapludalf) to determine N use efficiency and its partitioning in various plant parts of corn. Ammonium nitrate labeled either as 15 NH 4-N or 1S NO 3-N and applied at 50, 100, or 200 kg N ha" 1 was evaluated. Microplots (1.06 m 2) were established in the main N plots for 15 N fertilizer application, and main plots were used to determine grain yield. After the crop harvest, soil N alone, fertilizer N used by the crop, and fertilizer N remaining in inorganic and organic forms in the top 75 cm of the soil were measured. Grain yield response to N application was significant (P < 0.01). Recovery of applied fertilizer N in corn and weeds ranged from 43 to 57% and 3 to 5%, respectively. Nitrogen sources showed no significant differences with respect to N accumulation in corn. Only 17 to 20% of the fertilizer N was recovered in the grain. The amounts of soil N utilized by the corn was about threeto sixfold higher than the fertilizer N, suggesting extensive turnover of soil and fertilizer N through immobilization and mineralization. More N was recovered (21-63% of added N) in the soil from 15 NH 4 than from I5 NO, (6-38%). Loss of N (unaccounted for) ranged from 11 to 18% at 100 kg N ha-' and from 34 to 48% at 200 kg N ha-1. Nitrogen loss was higher in the plots receiving I5 NO, than 15 NH 4. Most of the fertilizer N remaining in the soil at the end of the growing season was in the organic fraction, suggesting immobilization into microbial and root biomass.
Limited water availability is a major constraint for cultivation of rice (Oryza sativa L.) in the traditional flooded systems, particularly in the semiarid regions of the world. Aerobic rice cultivation provides feasible alternative to traditional rice production in these regions, allowing significant water savings. Field experiments were conducted at the ANGR University Agricultural Research Station, India during 2009–2010 and 2010–2011 to compare crop growth, yield, and water savings under aerobic rice–maize (R–M) and flooded R–M rotation systems. The effect of aerobic rice on the succeeding maize crop was also studied. The total amount of water applied (including rainfall) in the aerobic plots was 967 and 645 mm compared to 1546 and 1181 mm in flooded rice system, during 2009 and 2010, respectively. This resulted in 37 to 45% water savings with the aerobic method. The soil moisture in aerobic treatment was maintained in the –30 to –40 kPa range throughout the crop growth. The aerobic rice system produced significantly lower grain yields in 2009 and 2010, where differences between flooded and aerobic rice were 39 and 15.4%, respectively. The yield differences were attributed to the differences in spikelet number per panicle and grain weight. Significant increase in yields was recorded in both systems with increased N rates up to 120 kg ha−1. Significantly higher yields were obtained in no‐till maize grown subsequent to the aerobic rice than flooded rice, possibly due to residual soil N and improved soil physical conditions.
Anaerobic lagoons and treatment wetlands are used worldwide to treat wastewater from dense livestock production facilities; however, there is very limited data on the hormonal activity of the wastewater effluent produced by these treatment systems. The objectives of this experiment were to measure (1) the hormonal activity of the initial effluent and (2) the effectiveness of a lagoon-constructed wetland treatment system for producing an effluent with a low hormonal activity. Wastewater samples were taken in April, July, and November 2004 and July 2005 from a lagoon-constructed wetland system at a swine farrowing facility. Estrogenic activity (in vitro E-screen assay), 17 beta-estradiol (E2), and testosterone concentrations (LC/MS-MS) were measured. A high correlation was found between estradiol equivalents determined by E-screen and LC/MS-MS (R2 = 0.82). Nutrient removal was measured to ensure that the wetlands were functioning in a manner similar to literature reports. Nutrient removals were typical for treatment wetlands: TKN 59-75% and orthophosphate 0-18%. Wetlands decreased estrogenic activity by 83-93%. Estrone was the most persistent estrogenic compound. Constructed wetlands produced effluents with estrogenic activity below the lowest equivalent E2 concentration known to have an effect on fish (10 ng/L or approximately 37 x 10(-12) M).
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