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El fósforo (P) orgánico puede comprometer una porción significativa del P total en los deshechos animales, sin embargo hay poca información del potencial de P orgánico para ser transferido desde los suelos hacia los caudales de agua. Nosotros examinamos la absorción de compuestos de P orgánico en suelos típicos del sureste Estadounidense, p.e., Arena Blanton (margoso, silíceo, térmico, Paleudult Grossarenic), marga de arcilla arenosa Cecil (fino, kaolinitico, térmico, Kanhapludult Tipivo), y una marga arenosa Belhaven (margoso, mixto, disico, térmico, Medisaprist Terrico). Se estudio el comportamiento de cuatro compuestos orgánicos de P: adenosina 5' -trifosfosfato (ATP), adenosina 5'-difosfato (ADP), adenosina 5'-monofosfato (AMP), e inositol hexafosfato (IHP); mientras que KH2PO4 (orto-P) fue usado como una referencia inorgánica. Se condujeron estudios de laboratorio para determinar los efectos de concentración (0-130 fLg P mL -1), pH (4.6-7.6), y propiedades de suelo en adsorcion de P. Todos los compuestos de P orgánico tuvieron una mayor adsorcion que los KH2PO4 en los suelos Cetiles y Blanton en todas los rangos y concentraciones de pH. En todo el suelo Belhaven, IHP tuvo una mayor sorcion seguida por KH2PO4 y nucleótidos (ATP, ADP, y AMP, respectivamente). Adsorcion de P orgánico estuvo positivamente correlacionada con materia orgánica del suelo y contenidos de Fe y Al. La mayor sorcion de algunos compuestos orgánicos de P sobre los de P-orto sugieren que estos compuestos pudiesen mostrar menor riesgo a la calidad del agua, aunque esta sorcion preferencial pudiese incrementar el P soluble en situaciones donde hay desplazamiento de P-orto por P orgánico agregado a los abonos.

Land application of animal manures and fertilizers has resulted in an increased potential for excessive P losses in runoff to nutrient-sensitive surface waters. The purpose of this research was to measure P losses in runoff from a bare Piedmont soil in the southeastern United States receiving broiler litter or inorganic P fertilizer either incorporated or surface-applied at varying P application rates (inorganic P, 0-110 kg P ha(-1); broiler litter, 0-82 kg P ha(-1)). Rainfall simulation was applied at a rate of 76 mm h(-1). Runoff samples were collected at 5-min intervals for 30 min and analyzed for reactive phosphorus (RP), algal-available phosphorus (AAP), and total phosphorus (TP). Incorporation of both P sources resulted in P losses not significantly different than the unfertilized control at all application rates. Incorporation of broiler litter decreased flow-weighted concentration of RP in runoff by 97% and mass loss of TP in runoff by 88% compared with surface application. Surface application of broiler litter resulted in runoff containing between 2.3 and 21.8 mg RP L(-1) for application rates of 8 to 82 kg P ha(-1), respectively. Mass loss of TP in runoff from surface-applied broiler litter ranged from 1.3 to 8.5 kg P ha(-1) over the same application rates. Flow-weighted concentrations of RP and mass losses of TP in runoff were not related to application rate when inorganic P fertilizer was applied to the soil surface. Results for this study can be used by P loss assessment tools to fine-tune P source, application rate, and application method site factors, and to estimate extreme-case P loss from cropland receiving broiler litter and inorganic P fertilizers.

Accurate descriptions of P leaching are important because excess P applied to soils can enter surface water via leaching and subsurface transport, thereby negatively impacting water quality. The objectives of this study were to monitor P leaching in soils with a long-term history of waste application, relate soil solution P concentrations to soil P status, and quantify P leaching losses. Soil solution was monitored for 20 mo with samplers installed at 45-, 90-, and 135-cm depths in two pits (1 X 3 X L5 m) in Autryville (loamy, siliceous, thermic Arenic Paleudults) and Blanton (loamy, siliceous, semiactive, thermic Grossarenic Paleudults) soils located in a grazed pasture in Sampson County, NC, which had received swine waste for >20 yr. Maximum soil solution P concentrations at 45 cm exceeded 18 mg L' in both soils. Soil solution P concentrations at 90 cm in the Blanton soil were similar to that at 45 cm indicating low P sorption. Soil solution P concentrations at 90 cm in the Autryville soil averaged 0.05 mg L-' compared to 10 mg L' at 45 cm. A split-line model related soil solution P concentration to the degree of phosphorus saturation (DPS), identifying a change point at 45% DPS. Phosphorus movement past 45 cm equaled or exceeded surplus P additions for both soils. Longterm waste applications resulted in DPS > 90%, high soil solution P concentrations, and substantial vertical P movement. Phosphorus leaching should be considered when assessing long-term risk of P loss from waste-amended soils.

Recurrent full‐sib family and reciprocal recurrent selection have resulted in significant increases in grain weight of crosses between the varieties of maize (Zea mays L.) Jarvis Golden Prolific and Indian Chief. The objectives of this study were to (i) compare increases due to 14 cycles of recurrent full‐sib family selection, and reciprocal recurrent selection for yield in maize and (ii) determine whether increased grain weights were accompanied by parallel increases in total dry matter and total N accumulation. Unless total dry matter acquisition increases in parallel with grain weight during selection, sustained root and shoot functions would be restricted by excessive diversion of carbohydrates to grain. After 14 selection cycles on sandy soils of the North Carolina coastal plain, grain weight, dry matter accumulation, and N accumulation in the population hybrid increased 23, 12, and 4%, respectively, with full‐sib family selection and 27, 21, and I0%, respectively, with reciprocal recurrent selection. Greater proportions of the dry matter and N accumulated were partitioned to grain after full‐sib family selection than after reciprocal recurrent selection. Therefore, photosynthate production after full‐sib family selection was not sufficient to fully satisfy both the demand by grain and the requirements for root and shoot processes. Reciprocal recurrent selection resulted in a greater increase in photosynthate production, so that the hybrid population was able to meet the demand for carbohydrate by higher grain yield and still sustain N acquisition by roots. The conclusions were also supported by heterosis for grain weight, total dry matter, and total N accumulation, which was greater after reciprocal recurrent selection than after full‐sib family selection. Selection to increase grain weight will result in efficient N acquisition only when the greater grain weight is supported by an adequate increase in photosynthate production.

Because of their chemical and physical similarities, plant uptake of S and Se are closely related. Barley (Hordeum vulgare L.) and rice (Oryza sativa L.) were grown in greenhouse solution culture to examine the synergistic interactions between SO4 and Se 6+ in plant uptake. In the presence of low concentrations of solution SO4, shoot and root yields were decreased with additions of Se 6+ . However, when SO 4 was present in elevated concentrations, no Se-induced yield reduction occurred. A synergistic interaction between SO4 and Se 6+ caused an increase in the shoot S concentrations with increasing concentrations of Se 6+ at low SO4 solution concentrations. At elevated SOn concentrations, no synergism was osberved. Selenium had a lesser effect on the S concentration in plant roots.