Thomas L. Thompson

Salicornia bigelovii Torr.: An Oilseed Halophyte for Seawater Irrigation

The terrestrial halophyte, Salicornia bigelovii Torr., was evaluated as an oilseed crop for direct seawater irrigation during 6 years of field trials in an extreme coastal desert environment. Yields of seed and biomass equated or exceeded freshwater oilseed crops such as soybean and sunflower. The seed contained 26 to 33 percent oil, 31 percent protein, and was low in fiber and ash (5 to 7 percent). The oil and meal were extracted by normal milling equipment, and the oil was high in linoleic acid (73 to 75 percent) and could replace soybean oil in chicken diets. The meal had antigrowth factors, attributed to saponins, but could replace soybean meal in chicken diets amended with the saponin antagonist, cholesterol. Salicornia bigelovii appears to be a potentially valuable new oilseed crop for subtropical coastal deserts.

Leaf nitrogen concentration of wheat subjected to elevated [CO2] and either water or N deficits

Leaf N concentration is important because it is associated with the CO2 assimilatory capacity of crops, and in grasslands, it is an important determinant of forage nutritive value. Consequently, the productivity of both domestic and native animals in future global environments may be closely linked to possible changes in leaf N concentration of grasses. Since grasslands are frequently subjected to water-deficit or N-deficit conditions, it is important to investigate the interactive responses between elevated [CO2] and these stress conditions. Therefore, this 4-year research program was undertaken with wheat (Triticum aestivum L.) as a model system for forage grasses, to document the potential changes in leaf N concentration in response to global environment changes. Wheat crops grown under field conditions near Phoenix, AZ, USA, were subjected to elevated [CO2] and either water-deficit or N-deficit treatments using large Free Air Carbon dioxide Enrichment (FACE) arrays. Surprisingly, the elevated [CO2] treatment under optimum conditions resulted in little change in leaf N concentration. Therefore, no change in the nutritive value of forage from highly managed pastures would be expected. Further, water-deficit treatment had little influence on leaf N concentration. To some extent, the lack of response to the water-deficit treatment resulted because severe deficits did not develop until late in the growing seasons. Only on one date late in the season was the water-deficit treatment found to result in decreased leaf N concentration. The low N treatment in combination with elevated [CO2], however, had a large influence on leaf N concentration. Low levels of applied N resulted in decreased leaf N concentration under both [CO2] treatments, but the lowest levels of leaf N concentration were obtained under elevated [CO2] through much of the growing season. These results point to a potential problem with grasslands in that the nutritive value of the forage consumed by animals will be decreased under future global environment changes.

CO2 enrichment and soil nitrogen effects on wheat evapotranspiration and water use efficiency

Evapotranspiration (ET) and water use efficiency (WUE) were evaluated for two spring wheat crops, grown in a well-watered, subsurface drip-irrigated field under ambient (about 370 mmol mol 1 during daytime) and enriched (200mmol mol 1 above ambient) CO2 concentrations during 1995‐1996 and 1996‐1997 in Free-Air CO2 Enrichment (FACE) experiments in central Arizona. The enriched (FACE) and ambient (Control) CO2 treatments were replicated in four, circular plots, each 25 m in diameter. Two soil nitrogen (N) treatments, ample (High N) and limited (Low N), were imposed on one-half of each circular plot. Wheat ET, determined using soil water balance procedures, was significantly greater in High N than Low N treatments starting in late-March (anthesis) during both years. Differences in ET between CO2 treatments during the seasons were generally small and not statistically significant, however, there was a tendency for the ET to be lower for FACE than Control under the High N treatment. The reduction in the cumulative seasonal ET due to FACE averaged 3.7 and 4.0% under High N and 0.7 and 1.2% under Low N in the first and second years, respectively. However, WUE (grain yield per unit seasonal ET) was significantly increased for the FACE treatment under both soil N treatments. For the High N treatment, the WUE was 19 and 23% greater for FACE than Control and for the Low N treatment the WUE was 12 and 7% greater for FACE than Control in the 2 years, respectively. Published by Elsevier Science B.V.

Elevated CO2 stimulates soil respiration in a FACE wheat field

Summary Understanding the response of soil carbon (C) dynamics to higher atmospheric CO 2 concentrations is critical for evaluating the potential for soil C sequestration on time scales of decades to centuries. Here, we report on changes in soil respiration under Free-Air CO 2 Enrichment (FACE) where spring wheat was grown in an open field at two CO 2 concentrations (ambient and ambient+200 μmol mol −1 ), under natural meteorological conditions. FACE increased soil respiration rates by 40—70% during the peak of wheat growth. On the FACE plots, stable C isotopic composition of soil CO 2 was used to partition the soil CO 2 flux into C from rhizosphere respiration and decomposition of pre-existing C. Decomposition contributed 100% of the soil CO 2 flux before crop growth commenced, and only 35—45% of the flux at the peak of the growing season. Decomposition rates were not correlated with soil temperature, but rhizosphere respiration rates were strongly correlated with green leaf area index. Ein Verstandnis der Antwort der Kohlenstoff-Dynamik (C) im Boden auf hohere CO 2 -Konzentrationen in der Atmosphare ist bedeutsam fur die Bewertung des Potentials fur die C-Sequestration in Zeitraumen von Jahrzehnten bis Jahrhunderten. Hier berichten wir uber Veranderungen in der Bodenatmung unter Free-Air CO 2 Enrichment (FACE), bei dem Sommerweizen in einem offenen Feld unter zwei CO 2 -Konzentrationen (Umgebung und Umgebung + 200 (mol mol −1 ) und unter naturlichen meteorologischen Bedingungen angebaut wurde. FACE erhohte die Bodenatmungsraten um 40—70% wahrend des Maximums des Weizenwachstums. Auf den FACE Plots wurde die Zusammensetzung an stabilen C Isotopen des Boden-CO 2 genutzt, um den Boden CO 2 -Fluss zu C durch Rhizospharen-Atmung von der Zersetzung von zuvor existierendem C zu trennen. Die Zersetzung trug 100% des Boden-CO 2 -Flusses vor dem Beginn des Weizenwachstums bei, und nur 35—45% des Flusses wahrend des Maximums des Wachstums. Die Zersetzungsraten waren nicht mit der Bodentemperatur korreliert, aber die Rhizospharen-Atmungsraten waren eng korreliert mit dem grunen Blattflachen-Index.

Acclimation response of spring wheat in a free-air CO2 enrichment (FACE) atmosphere with variable soil nitrogen regimes. 1. Leaf position and phenology determine acclimation response

We have examined the photosynthetic acclimation of wheat leaves grown at an elevated CO2 concentration, and ample and limiting N supplies, within a field experiment using free-air CO2 enrichment (FACE). To understand how leaf age and developmental stage affected any acclimation response, measurements were made on a vertical profile of leaves every week from tillering until maturity. The response of assimilation (A) to internal CO2 concentration (Ci) was used to estimate the in vivo carboxylation capacity (Vcmax) and maximum rate of ribulose-1,5-bisphosphate limited photosynthesis (Asat). The total activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and leaf content of Rubisco and the Light Harvesting Chlorophyll a/b protein associated with Photosystem II (LHC II), were determined. Elevated CO2 did not alter Vcmax in the flag leaf at either low or high N. In the older shaded leaves lower in the canopy, acclimatory decline in Vcmax and Asat was observed, and was found to correlate with reduced Rubisco activity and content. The dependency of acclimation on N supply was different at each developmental stage. With adequate N supply, acclimation to elevated CO2 was also accompanied by an increased LHC II/Rubisco ratio. At low N supply, contents of Rubisco and LHC II were reduced in all leaves, although an increased LHC II/Rubisco ratio under elevated CO2 was still observed. These results underscore the importance of leaf position, leaf age and crop developmental stage in understanding the acclimation of photosynthesis to elevated CO2 and nutrient stress.

A petiole sap nitrate test for broccoli

Abstract Nitrogen (N) status of vegetable crops is often monitored by analysis of dried plant tissues. However, dry tissue analysis often causes a significant delay between sampling and analysis. This study was conducted to examine the accuracy of a portable nitrate meter for determining petiole sap nitrate (NO3) contents, and the relationship between NO3‐N concentration in fresh petiole sap and in dried petiole tissue of broccoli grown in southern Arizona during the 1993–94 and 1994–95 winter growing seasons. Experiments were factorial combinations of three irrigation rates and four N rates, both ranging from deficient to excessive. Petioles were sampled throughout each season, and split for sap and dry tissue analysis. A linear correlation was obtained between the two measurements in both seasons, with no consistent effect due to irrigation treatment or crop maturity. The regression coefficients did not differ among seasons. Therefore, a combined regression equation: Y=343+0.047X (r2 = 0.799) was derive...

Fertigation Frequency for Subsurface Drip-Irrigated Broccoli

Yosef and Sagiv, 1982; Stark et al., 1983; Burt et al., 1995). However, very few studies have shown a benefit Subsurface-drip irrigation and fertigation with fluid N fertilizer of frequent or continuous fertigation compared with sources offers substantial flexibility for N fertilizer management. Fertiless frequent fertigation. Bar-Yosef and Sagiv (1982) gation events can be scheduled as often as irrigation, up to several times per day. However, because of system or management constraints practiced continuous fertigation of surface drip-irrivery frequent fertigation may not be possible or desirable for some gated tomato (Lycopersicum esculentum L.) with congrowers. Optimum fertigation interval for subsurface drip-irrigated centrations of 100 to 200 mg N L 1 in the irrigation crops has not been well researched. A 3-yr field experiment was water. However, this resulted in N applications 1000 conducted on a sandy loam soil in southern Arizona with subsurface kg N ha 1, far greater than N uptake by the plants; drip-irrigated broccoli (Brassica olearacea L. Italica) to i) determine consequently N use efficiency (NUE) was as low as the effects of N rate and fertigation frequency on crop yield, quality, 30%. Stark et al. (1983) determined that 75 mg N L 1 and crop N status, and ii) estimate a N balance. Broccoli was planted was the optimum concentration for continuous fertigain two rows per raised bed 1.02 m apart, with one drip line buried tion of tomato with surface-drip irrigation. Bhella and 0.15 to 0.20 m deep within each bed. The experiment included factorial Wilcox (1985) advocated continuous fertigation of surcombinations of two N rates and four fertigation frequencies (intervals of 1, 7, 14, and 28 d). Broccoli marketable yield and quality were face drip-irrigated cantaloupe (Cucumis melo L.) with responsive to N rate, but not to increased fertigation frequency. Dur150 and 50 mg N L 1 during vegetative and reproductive ing one of three seasons, fertigation frequency significantly (P 0.05) stages, respectively. affected crop N uptake, but there was no trend of increasing N uptake Few studies are reported in which the effects of differwith increasing fertigation frequency. Unaccounted fertilizer N and ent drip-fertigation frequencies on yield and quality of apparent N use efficiency (ANUE) were calculated for two seasons. annual crops are compared. Several researchers have Unaccounted fertilizer N averaged 20 and 75 kg ha 1 and ANUE 90 compared applications of all N soil-applied preplant and 81% with 250 and 350 kg N ha 1 applied, respectively. Neither with a combination of preplant soil-applied and in-seawas significantly affected by fertigation frequency. We conclude, son fertigated N on tomato. Locascio et al. (1985, 1989) therefore, that for broccoli production with subsurface-drip irrigation found that surface drip-irrigated tomato yields were on sandy loam or finer soils, fertigation can be applied as infrequently as monthly, without compromising crop yield or quality, or causing higher with 40% of the N applied preplant and 60% excessive N losses. applied by fertigation, compared with all N applied preplant on sandy soils in Florida. Dangler and Locascio (1990) found that yield of surface drip-irrigated tomato was higher on a fine sand when 50% of fertilizer N M studies have demonstrated drip-irrigated crop response to N (e.g., Bar-Yosef and Sagiv, was soil-applied before planting, than when all N was applied via fertigation. Cook and Sanders (1991) ex1982; Thompson et al., 2002a). Optimum N rates for many drip-irrigated crops have been published (Hochamined the effect of fertigation frequency (daily to monthly) on subsurface drip-irrigated tomato yields in muth, 1992; Hartz, 1994). Drip irrigation and fertigation with fluid N fertilizer sources offer what is probably two South Carolina soils. Daily or weekly fertigation significantly increased yield compared with monthly ferthe ultimate in flexibility for N fertilizer management. Fertigation events can be scheduled as often as irritigation, but there was no advantage of daily over weekly fertigation on a loamy sand. The same fertigagation, up to several times per day. However, because of system or management constraints very frequent tion frequencies resulted in no differences in yield and quality on a loamy fine sand soil. Locascio and Smajstrla fertigation may not be possible or desirable for some growers. Optimum fertigation interval for drip-irrigated (1995) found that surface drip-irrigated tomato yields with daily fertigation were not increased compared with crops, although important, has not been thoroughly researched (Hartz, 1994). yields with weekly fertigation on a fine sand. Locascio et al. (1997) found that there were no differences in Various authors have recommended very frequent or continuous fertigation for drip-irrigated crops (i.e., Baryield or quality of surface drip-irrigated tomato fertigated either six or 12 times per season. Similarly, yields of surface drip-irrigated pepper (Capsicum annum L.) T.L. Thompson, S.A. White, J. Walworth, and G.S. Sower, 429 Shantz, were not affected by fertigation interval (11 or 22 d) on Dep. of Soil, Water and Environmental Science, University of Aria loamy sand soil (Neary et al., 1995). zona, Tucson, AZ 85721. Received 27 June 2002. *Corresponding author (thompson@ag.arizona.edu). Abbreviations: ANUE, apparent N use efficiency; NUE, N use efficiency. Published in Soil Sci. Soc. Am. J. 67:910–918 (2003).

Effect of Irrigation Water Contaminated with Uranium Mill Tailings on Sudan Grass, Sorghum vulgare var. sudanense, and Fourwing Saltbush, Atriplex canescens

A greenhouse experiment was carried out to estimate the effects of irrigation water quality on chemical uptake and productivity of Sudan grass (Sorghum vulgare var. sudanense) and fourwing saltbush (Atriplex canescens). Water and soil were obtained from an inactive U ore processing site near Tuba City, Arizona. Two observation wells provided the irrigation water. One was located upgradient from the contaminated site, and was located in the center of the plume downgradient from the area contaminated by the milling operations. A 50/50 mix of the two well waters was used as a third treatment. Concentrations of Se and U in aboveground tissues of saltbush were significantly (< 0.05) elevated when irrigated with the undiluted contaminated water, but not to unacceptable levels. In the case of Sudan grass, Mo, Se, U, NO3 -N, and S were significantly (< 0.05) elevated in the contaminated water treatment, and all except NO3 -N were elevated with the diluted contaminated water, but again within acceptable limits. Saltbush productivity was not significantly (< 0.05) affected by the three irrigation treatments. Sudan grass aboveground biomass results suggest that the undiluted contaminated plume water could be used for effective crop production, although productivity was significantly better with the nutrient-amended baseline water and the diluted contaminated water. Root biomass was significantly greater in the baseline water irrigation.

PLANT UPTAKE RESPONSE TO METALS AND NITRATE IN SIMULATED URANIUM MILL TAILINGS CONTAMINATED GROUNDWATER

Carrots, squash, and Sudan grass were irrigated with groundwater amended with manganese, molybdenum, selenium, and uranium stock solutions to simulate a range of concentrations found at ten inactive uranium ore milling sites to determine plant tissue levels after a 90 day growth period in sand in a greenhouse. Sudan grass was also dosed with a series of nitrate concentrations. Except for squash response to uranium, all plantsshowed an increased accumulation of each metal, someto unacceptable levels, with increased metal concentration dose. Squash did not accumulate uranium at any dose tested. Increased nitrate in the irrigation water did not have a major influence on Sudan grass accumulation of any metal.

Mechanisms of range expansion and removal of mesquite in desert grasslands of the Southwestern United States

During the last 150 years, two species of mesquite trees in the Southwestern United States have become increasingly common in what formerly was desert grassland. These trees have spread from nearby watercourses onto relatively xeric upland areas, decreasing rangeland grass production. Management attempts to limit or reverse this spread have been largely unsuccessful. This paper reviews studies regarding mesquite natural history and management strategies, emphasizing studies published during the past decade. Mesquite possess a deep root system and are capable of fixing atmospheric N, rendering them capable of accessing resources unavailable to other plants in open rangeland. Their seeds, which remain viable for decades, have a hard exocarp and require scarification before germination. Consumption by cattle provides a means of scarification and seed dispersal, and is a major factor contributing to the spread of mesquite in open rangelands. Increases in atmospheric CO2 and winter precipitation during the past century also contribute to enhanced seed germination. Removal techniques have included herbicides, prescribed burning, grazing reduction, and mechanical removal. For increased effectiveness of these techniques, management goals must be clearly articulated; these goals include complete removal, no removal, and limited removal. Of these, limited removal appears the most feasible, using an initial herbicide application followed by periodic prescribed burning.