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Th e loss of major nutrients can be high in rice (Oryza sativa L.) fi elds, particularly rainfed rice, where water fl owing from fi eld to fi eld during periods of high rainfall not only reduces the nutrient use effi ciencies but also has the potential for environmental degradation. We examined the infl uence of deep point placement of N, P, and K briquettes compared to broadcast incorporation of N, P, and K on fl oodwater nutrient loads aft er fertilizer application and on the performance of wet season rice in a Vertisol. Broadcast application of N as urea resulted in an average 10 times higher amounts of ammonium N in fl oodwater compared to deep placement of urea briquette. Th e broadcast application of single superphosphate resulted in 67 times higher amounts of P in fl oodwater than plots receiving deep placed P. Th e fl oodwater NH 4 + -N and P content in the deep placement treatments were negligible-similar to fl oodwater N and P content without fertilizer application. Th e fl oodwater K amounts were also significantly lower with deep placed N-P-K briquettes. Signifi cantly higher grain and straw yields, total N, P, and K uptake, and N and P use effi ciencies were observed with deep placement of N-P-K compared to broadcast application of N-P-K. Deep placed N-P briquettes gave signifi cantly higher grain yield, straw biomass, total P and K uptake, apparent P recovery, and agronomic N and P use effi ciencies when plant spacing was reduced from 20 by 20 cm to 20 by 10 cm. Closer plant spacing led to better utilization of P and K and provided opportunities for deep placement of N-P or N-P-K briquettes in soils with low available P. Combining site specifi c characteristics (high soil pH, low percolation rate, high rainfall and surface runoff s) with plant spacing and N-P-K briquettes prepared based on site-specifi c nutrient requirements off ers potential for higher yields, improved fertilizer use effi ciency, balanced fertilization, and reduced nutrient losses.

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Summary Effects of CO2 enrichment on leaf transpiration are well‐documented, but our understanding of how CO2 interacts with other variables to regulate evapotranspiration from plant communities is more limited. A series of weighing lysimeters in which tallgrass prairie species had been planted were exposed to a subambient to elevated gradient in CO2 in a field chamber. Lysimeters with intact monoliths of three soil types were represented along the CO2 gradient. We used regression analysis to determine how CO2 effects on evapotranspiration per unit of soil surface area (ETsoil) and per unit of leaf area (ETla) depended on variation in leaf area index (LAI) and diurnal changes in environmental variables during the initial 6 weeks of CO2 treatment. CO2 enrichment reduced ETsoil and ETla, and together with air temperature and LAI accounted for most of the variance in daily values of evapotranspiration explained by multiple regression models. The CO2 effect on ETsoil did not depend on values of other variables, but CO2 enrichment reduced ETla most at relatively low air temperatures and low LAI for all soils combined. Higher temperatures countered the CO2 effect by increasing ETla more at elevated than subambient CO2. Higher LAI countered the CO2 effect by decreasing ETla more at subambient than elevated concentrations. Plant (LAI) and environmental effects on ETla differed among soils, possibly because plant growth patterns and physiology differed among soils. Our results imply that the CO2 effect on evapotranspiration per unit of leaf area will vary with seasonal change in temperature and LAI, independent of seasonal shifts in leaf age and physiological activity.

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Open field host selection and behavior by tamarisk beetles (Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars (Tamarix spp.) and risks to non-target athel (T. aphylla) and native Frankenia spp. Open field host selection and behavior by tamarisk beetles (Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars (Tamarix spp.) and risks to non-target athel (T. aphylla) and native Frankenia spp. , an evergreen tree used for shade and as a windbreak in the southwestern U.S. and México, and occasionally feed on native Frankenia spp. plants. The ability of tamarisk beetles to establish on these potential field hosts was investigated in the field. In no-choice tests in bagged branches, beetle species from Crete and Sfax, Tunisia produced 30-45% as many egg masses and 40-60% as many larvae on athel as on saltcedar. In uncaged choice tests in south Texas, adult, egg mass and larval densities were 10-fold higher on saltcedar than on adjacent athel trees after 2 weeks, and damage by the beetles was 2-to 10-fold greater on saltcedar. At a site near Big Spring, in west-central Texas, adults, egg masses and 1st and 2nd instar larvae were 2-to 8-fold more abundant on saltcedar than on athel planted within a mature saltcedar stand being defoliated by Crete beetles, and beetles were 200-fold or less abundant or not found at all on Frankenia. At a site near Lovelock, Nevada, damage by beetles of a species collected from Fukang, China was 12-78% higher on saltcedar than on athel planted among mature saltcedar trees undergoing defoliation. The results demonstrate that 50-90% reduced oviposition on athel and beetle dispersal patterns within resident saltcedar limit the ability of Diorhabda spp. to establish populations and have impact on athel in the field. Published by Elsevier Inc.

Mielnick, P. C.; Dugas, W. A.; Johnson, H. B.; Polley, H. W.; and Sanabria, J., "Net grassland carbon flux over a subambient to superambient CO2 gradient" (2001). Publications from USDA-ARS / UNL Faculty. 434. http://digitalcommons.unl.edu/usdaarsfacpub/434 Net grassland carbon¯ux over a subambient to superambient CO 2 gradient AbstractIncreasing atmospheric CO 2 concentrations may have a profound effect on the structure and function of plant communities. A previously grazed, central Texas grassland was exposed to a 200-mmol mol ±1 to 550 mmol mol ±1 CO 2 gradient from March to mid-December in 1998 and 1999 using two, 60-m long, polyethylenecovered chambers built directly onto the site. One chamber was operated at subambient CO 2 concentrations (200±360 mmol mol ±1 daytime) and the other was regulated at superambient concentrations (360±550 mmol mol ±1 ). Continuous CO 2 gradients were maintained in each chamber by photosynthesis during the day and respiration at night. Net ecosystem CO 2¯u x and end-of-year biomass were measured in each of 10, 5-m long sections in each chamber. Net CO 2¯u xes were maximal in late May (c. day 150) in 1998 and in late August in 1999 (c. day 240). In both years,¯uxes were near zero and similar in both chambers at the beginning and end of the growing season. Average daily CO 2¯u x in 1998 was 13 g CO 2 m ±2 day ±1 in the subambient chamber and 20 g CO 2 m ±2 day ±1 in the superambient chamber; comparable averages were 15 and 26 g CO 2 m ±2 day ±1 in 1999. Flux was positively and linearly correlated with end-of-year above-ground biomass but¯ux was not linearly correlated with CO 2 concentration; a ®nding likely to be explained by inherent differences in vegetation. Because C 3 plants were the dominant functional group, we adjusted average daily¯ux in each section by dividing the¯ux by the average percentage C 3 cover. Adjusted¯uxes were better correlated with CO 2 concentration, although scatter remained. Our results indicate that after accounting for vegetation differences, CO 2¯u x increased linearly with CO 2 concentration. This trend was more evident at subambient than superambient CO 2 concentrations.