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During the last several decades, members of the SSSA have discussed several trends related to soil science education, including: (i) declining academic programs and course offerings at land grant universities, (ii) decreased enrollments, and (iii) improved employment opportunities for soil science graduates (SSSA, 2006; Ferris et al., 2010). The SSSA Advocacy/Education Task Force met in 2007 and concluded that quantitative survey information was needed to document trends in soil science academic programs, student enrollment, faculty, and job opportunities for graduates. Suggested survey topics included: · Has the recognition of soil science as a distinct discipline increased or decreased? · How has the job market changed during the past decade, and how will job opportunities for soil scientists change in the future? · How have undergraduate and graduate soils curricula changed during the last decade? · Has enrollment in soil science degree programs and courses changed during the past decade? · Has there been a change in the degree programs of students enrolling in soils courses in the past decade? · Have soil science programs been combined with other programs? Therefore, the objective of the survey was to quantify trends in student enrollment, faculty positions, pertinent educational issues in soil and related sciences, and career or job opportunities and trends. Expected outcomes included a better understanding of current educational practices and trends, and identification of specific opportunities for SSSA to enhance the practice and profession of soil science.

Moby Dick: Jonah, Ahab, and Ishmael Father Mapple’s sermon on Jonah in Moby-Dick is a biblical narrative in the form of a short story, allegorically structured as a parable on nationalist hatred and divine compassion. It takes its point of departure from the obscure figure of a pre-exilic prophet, borrowed from the brief story about the reign of Jeroboam II (2 Kings 14.23-29). Jeroboam was king in Samaria for forty-one years. He not only saved Israel from extinction, but also “restored” its utopian “Solomonic” borders (1 Kings 8.65) south to the Dead Sea and north as far as the great Syrian cities of Hamath and Damascus. Jeroboam’s great success is attributed to his obedience to the advice of the prophet, Jonah Ben Amittai, who was from the town of Gath ha-Hepher in the Lower Galilee. This prophet Jonah incited Jeroboam to a holy war with the ambition of bringing all of Yahweh’s land back to Israel.1 The Book of Jonah’s use of this figure—a classic biblical portrayal of the prophet of Yahweh’s judgment, ever zealous for Israel’s messianic victory over nations in uproar (Psalms 2.1-2)—offers a man who is eager to complete the great victories of 2 Kings by bringing Yahweh’s judgment to the heart of the empire itself. This Jonah wishes to be another Elijah in his zeal: a veritable Nahum, a prophet of doom to bring divine destruction on the great city of Nineveh (Nahum 1-3). The book opens as Yahweh tells Jonah that the news of the great evil of Assyria’s Nineveh has come to him (Jonah 1.2). This same motif is used in Genesis 18.21 when Yahweh tells Abraham about his plans to destroy the evil city of Sodom. Although in Genesis, Abraham had argued against Yahweh that the innocent not be destroyed with the guilty, in Jonah’s book, the prophet is no Abraham, one in whom all the nations of the world are to be blessed (Genesis 12.3). Jonah knows already that his Yahweh has become “a gracious God and merciful, slow to anger and abounding in

In subsurface drip irrigation (SDI) systems, water constraints to cotton (Gossypium hirsutum L.) production are greatly minimized and N management becomes the main priority. Injecting N fertilizer into SDI systems should, in theory, be as efficient as the irrigation delivery system itself. The objective of this study was to test duration of N injections, addition of the nitrification inhibitor ammonium thiosulfate (ATS), and using canopy spectral reflectance to guide N injections in a 2-yr study of SDI cotton in Lubbock, TX. For a 1400 kg ha -1 expected lint yield, the N fertilizer rate was 170 kg N ha -1 minus the 0- to 0.6-m soil NO 3 -N and an estimate of irrigation water NO 3 (20 and 30 kg N ha -1 for 2005 and 2006). We tested injection of urea-NH 4 NO 3 (UAN) between first square and early bloom, and first square and peak bloom. There was no effect of timing or ATS on lint yield. Reflectance-based N management up to peak bloom resulted in savings of 28 and 17 kg UAN-N ha -1 for 2005 and 2006, respectively, compared with soil-test-based N fertigation. Lint yields were similar between reflectance-based UAN management (1814 kg ha -1 ) and UAN injected up to peak bloom based on soil test NO3 (1880 kg ha -1 ). Nitrogen fertilizer recovery at first open boll was not affected by treatment but was high (62-75%). Flux of N 2 O + N 2 was low (800-2100 g N ha -1 ) in both years and was not different between fertilized and unfertilized plots. Residual 0- to 1.2-m soil profile NO3 after 2 yr was not affected by N fertigation treatments. Nitrogen fertilizer injections in SDI cotton are utilized very efficiently, and spectral-reflectance-based approaches have potential to reduce N fertilizer inputs.

Salts that accumulate near the soil surface with subsurface drip irrigation (SDI) can hinder the establishment of succeeding direct-seeded crops. To prevent crop loss or yield reduction, producers rely on sprinklers for germination, which is often expensive and requires added capital inputs. Predicting salt movement and accumulation with SDI will allow producers to anticipate the need for sprinkler irrigation for salt control. The HYDRUS-2D model was used to model salt accumulation from an SDI system on successive crops of cantaloupe (Cucumis melo L. ssp. melo var. cantalupensis Naudin) and broccoli (Brassica oleracea L. var. italica Plenck) with two tape depths (18 and 25 cm), different germination practices (germination with SDI and with sprinklers), and water salinity (1.5 and 2.6 dS m -1 ). Predicted saturated-paste electrical conductivity (ECe) values from HYDRUS-2D were significantly correlated with actual ECe data obtained from field experiments (r 2 = 0.08-0.93). After Season 1, the correlation coefficients were highly variable, with the majority of model ECe values being higher than field data. Season 2 results indicated a much stronger relationship, with R 2 values as high as 0.93. Model predictions for Season 2 showed underprediction of ECe when compared with actual ECe. Relationships between model-predicted ECe and actual ECe resulted in a slope of nearly 1.0 for all treatments and a y intercept close to -1 dS m -1 . A better understanding of the processes that occur at the field scale, such as root growth, root distribution, and plant water uptake, is essential for modeling water and solute transport with SDI. A better characterization of evapotranspiration from SDI is required to accurately model salt accumulation.

The impacts of increasing atmospheric CO 2 , an important greenhouse gas, on soil microbial production and consumption of other greenhouse gases such as N 2 O are uncertain. This study was conducted during the 1998 and 1999 summer growing seasons at the Free-Air CO 2 Enrichment (FACE) site in Maricopa, AZ. The objective was to measure N 2 O and denitrification emission rates in a C 4 sorghum [Sorghum bicolor (L.) Moench] production system with ample and limited flood irrigation rates under FACE (seasonal mean = 579 μmol mol -1 ) and control (seasonal mean = 396 μmol mol -1 ) CO 2 . Plots were sampled for N 2 O flux using both chamber and intact incubated soil core techniques. Nitrogen gas (N 2 O plus N 2 ) emissions were measured using intact incubated soil cores with C 2 H 2 inhibition. Nitrous oxide emissions measured with chambers increased markedly after irrigation and fertilization following prolonged periods without water under both elevated and control CO 2 conditions. Within 5 d of fertilization and irrigation, N 2 O emissions measured with chambers were 250 g N 2 O-N ha -1 d -1 . Seasonal cumulative N 2 O-N emissions measured using chambers were 500 g N 2 O-N ha -1 d -1 ) coming with >55% WFPS. Neither soil NO 3 - nor soil organic C alone limited N gas emissions. Elevated CO 2 did not result in increased N 2 O or N-gas emissions with either ample or limited irrigation.

Microsprinklers allow precise control of irrigation water applications and offer the potential for higher efficiency of water and fertilizer use compared with flood irrigation. A field experiment was conducted during 1999‐2002 in central Arizona (AZ) to evaluate effects of various N rates and fertigation frequencies on fruit yield and quality, leaf N concentration, and residual soil N of ‘Newhall’ navel oranges (Citrus sinensis) on ‘Carrizo’ citrange (Porcirus trifoliata x Citrus sinensis) rootstock (planted in 1997) grown in a Gilman (coarse-loamy, mixed, superactive, calcareous, hyperthermic Typic Torrifluvents) fine sandy loam. The experiment included nonfertilized control plots and factorial combinations of three fertigation frequencies (27, 9, and 3 applications annually) and three N rates (68, 136, and 204 g N tree 21 yr 21 ). Maximum yields occurred at N rates of 105 to 153 g N tree 21 yr 21 for the fourth to the sixth growing seasons. The yield-maximizing N rates were equivalent to 17 to 34% of currently recommended N rates for citrus grown in AZ. Fruit and juice quality did not show significant response to N rate or fertigation frequency. Leaf N concentrations at yield-maximizing N rates were above the critical leaf tissue N range of 25 to 27 mg g 21 , indicating that this range may be too low for these ‘Newhall’ navel orange trees. During all three seasons, higher residual soil NO 3 concentrations resulted from the highest N rate. Our results suggest that optimum N rates for microsprinklerirrigated ‘Newhall’ navel oranges in AZ are lower than currently recommended N rates.

Fluid P fertilizers are commonly applied to established alfalfa (Medicago saliva L.) despite their higher cost compared to granular forms. The objectives of this experiment were to compare effects of fluid and granular P fertilizer on alfalfa yield, and availability and movement of P in the soil. The P fertilizers compared were fluid ammonium polyphosphate (APP, 10-34-0) applied in irrigation water and granular monoammonium phosphate (MAP, 11-52-0) topdressed and incorporated by flood irrigation on a calcareous soil at Maricopa, AZ. Fertilizer P was applied each December at rates of 1,2,3, and 5 g P m -2 . The soil was sampled about 1 mo later. In the first four cuttings of the first year, hay yields were 1358 g m -2 for APP and 1501 g m -2 for MAP. No differences in yield due to P source were measured in the remaining four cuttings of the first year, or in any cutting the second or third year. In the surface soil (0-7.6 cm), the bicarbonate extractable soil P averaged 44 mg kg -1 for APP and 7.1 for MAP. The depth of movement of the fertilizers was similar except in the first year where MAP moved deeper into the soil profile than APP. In this study, the higher cost of fluid APP compared with granular MAP was not recovered by increased yield. However, at low P rates, water-run APP may be more economical than topdressed MAP due to its low application cost.

Elevated concentrations of atmospheric CO 2 (C a ) are believed to raise sorghum [Sorghum bicolor (L.) Moench] productivity by improving water relations. In ecosys, water relations are simulated by solving for the canopy water potential (ψ c ) at which water uptake from a model of soil-root-canopy water transfer equilibrates with transpiration from the canopy energy balance. Simulated water relations were tested with ψ c , water uptake, and energy exchange measured under ambient (363 μmol mol -1 ) and elevated (566 μmol mol -1 ) C a and high vs. low irrigation in a free air CO 2 enrichment experiment during 1998 and 1999. Model results, corroborated by field measurements, showed that elevated C, raised ψ c and lowered latent heat fluxes under high irrigation and delayed water stress under low irrigation. Changes in ψ c modeled under ambient vs. elevated C a varied diurnally, with lower ψ c causing earlier midafternoon stomatal closure under ambient C a . Modeled changes in sorghum water status caused elevated C a to raise seasonal water efficiency under high and low irrigation by 20 and 26% (vs. 20 and 13% measured) in 1998 and by 9 and 27% (vs. 6 and 26% measured) in 1999. Ecosys was used to generate an irrigation response function for sorghum yield, which indicated that yields would rise by 13% for a range of irrigation rates if air temperatures were to rise by 3°C and C a by 50%. Current high sorghum yields could be achieved with 120 mm or 20% less irrigation water if these rises in temperature and C a were to occur.

Subsurface-drip irrigation and fertigation with fluid N fertilizer sources offers substantial flexibility for N fertilizer management. Fertigation events can be scheduled as often as irrigation, up to several times per day. However, because of system or management constraints very frequent fertigation may not be possible or desirable for some growers. Optimum fertigation interval for subsurface drip-irrigated crops has not been well researched. A 3-yr field experiment was conducted on a sandy loam soil in southern Arizona with subsurface drip-irrigated broccoli (Brassica olearacea L. Italica) to i) determine the effects of N rate and fertigation frequency on crop yield, quality, and crop N status, and ii) estimate a N balance. Broccoli was planted in two rows per raised bed 1.02 m apart, with one drip line buried 0.15 to 0.20 m deep within each bed. The experiment included factorial combinations of two N rates and four fertigation frequencies (intervals of 1, 7, 14, and 28 d). Broccoli marketable yield and quality were responsive to N rate, but not to increased fertigation frequency. During one of three seasons, fertigation frequency significantly (P ≥ 0.05) affected crop N uptake, but there was no trend of increasing N uptake with increasing fertigation frequency. Unaccounted fertilizer N and apparent N use efficiency (ANUE) were calculated for two seasons. Unaccounted fertilizer N averaged 20 and 75 kg ha -1 and ANUE 90 and 81% with 250 and 350 kg N ha -1 applied, respectively. Neither was significantly affected by fertigation frequency. We conclude, therefore, that for broccoli production with subsurface-drip irrigation on sandy loam or finer soils, fertigation can be applied as infrequently as monthly, without compromising crop yield or quality, or causing excessive N losses.

Production of broccoli (Brassica olearacea L. Italica ) in the south-western USA is highly dependent on inputs of water and N fertilizer to achieve optimum yields and quality. The water and N-response characteristics of subsurface drip-irrigated broccoli have not previously been reported. Field experiments were conducted in southern Arizona during 1993 through 1996. The objectives were to determine: (i) subsurface drip-irrigated broccoli response to a range of soil water tension (SWT), (ii) effects and interactions of water and N fertilizer inputs on crop yield and quality, and (iii) seasonal and daily N uptake. Experiments consisted of factorial combinations of three irrigation regimes (low, medium, and high) and four N rates (60-500 kg N ha -1 ). Irrigation was applied daily to maintain target SWT, and all N was applied by fertigation. With respect to marketable yield, the optimum SWT was 10 kPa in this sandy loam soil, as indicated by response surface models. Marketable yields across all treatments ranged from 18 Mg ha -1 . Marketable yield was significantly affected by N rate during all three seasons, and by SWT during two of three seasons. There were no significant SWT x N interactions for marketable yield. Quality parameters (head weight and diameter) were much more responsive to N rate than to SWT, and there were few significant SWT x N interactions for broccoli quality. Broccoli accumulated up to 320 kg N ha -1 in the aboveground biomass, and N uptake fluxes were as high as 5 kg N ha -1 d -1 at the first bud growth stage (825-1000 heat units after planting [HUAP]).

Summary • Sorghum (Sorghum bicolor) was grown for two consecutive seasons at Maricopa, AZ, USA, using the free-air CO2 enrichment (FACE) approach to investigate evapotranspiration of this C4 plant at ample and limited water supplies. • Crop evapotranspiration (ET) was measured using two CO2 concentrations (control, c. 370 µmol mol−1; FACE, ambient +200 µmol mol−1) and two irrigation treatments (well watered and water-limited). Volumetric soil water content was measured before and after each irrigation using neutron scattering techniques. • Averaged over both years, elevated CO2 reduced cumulative ET by 10% when plants were given ample water and by 4% under severe drought stress. Water-use efficiency based on grain yield (WUE-G) increased, due to CO2 enrichment, by 9% and 19% in wet and dry plots, respectively; based on total biomass, water-use efficiency (WUE-B) increased by 16% and 17% in wet and dry plots, respectively. • These data suggest that in the future high-CO2 environment, water requirements for irrigated sorghum will be lower than at present, while dry-land productivity will increase, provided global warming is minimal.

Summary • To determine the response of C4 plants to elevated CO2 it is necessary to establish whether young leaves have a fully developed C4 photosynthetic apparatus, and whether photosynthesis in these leaves is responsive to elevated CO2. • The effect of free-air CO2 enrichment (FACE) on the photosynthetic development of the C4 crop Sorghum bicolor was monitored. Simultaneous measurements of chlorophyll a fluorescence and carbon assimilation were made to determine energy utilization, quantum yields of carbon fixation (φCO2) and photosystem II (φPSII), as well as photorespiration. • Assimilation in the second leaf of FACE plants was 37% higher than in control plants and lower apparent rates of photorespiration at growth CO2 concentrations were exhibited. In these leaves, φPSII : φCO2 was high at low atmospheric CO2 concentration (Ca) due to overcycling of the C4 pump and increased leakiness. As Ca increased, φPSII : φCO2 decreased as a greater proportion of energy derived from linear electron transfer was used by the C3 cycle. • The stimulation of C4 photosynthesis at elevated Ca in young leaves was partially due to suppressed photorespiration. Additionally, elevated Ca enhanced energy-use efficiency in young leaves, possibly by decreasing CO2 leakage from bundle sheath cells, and by decreasing overcycling of the C4 pump.

Summary • The likely consequences of future high levels of atmospheric CO 2 concentration on wheat ( Triticum aestivum L.) grain nutritional and baking quality were determined. • Two free-air CO 2 enrichment (FACE; 550 mmol mol - 1 ) experiments were conducted at ample (Wet) and limiting (Dry) levels of irrigation, and a further two experiments at ample (High-N) and limiting (Low-N) nitrogen concentrations. Harvested grain samples were subjected to a battery of nutritional and bread-making quality tests. • The Dry treatment improved grain quality slightly (protein +2%; bread loaf volume +3%). By contrast, Low-N decreased quality drastically (protein - 36%; loaf volume - 26%). At ample water and N, FACE decreased quality slightly (protein - 5%; loaf volume - 2%) in the irrigation experiments and there was no change in the nitrogen experiments. At Low-N, FACE tended to make the deleterious effects of Low-N worse (protein - 33% and - 39%, at ambient CO 2 and FACE, respectively; loaf volume - 22% and - 29% at ambient CO 2 and FACE, respectively). • The data suggest that future elevated CO 2 concentrations will exacerbate the deleterious effects of low soil nitrogen on grain quality, but with ample nitrogen fertilizer, the effects will be minor.

Changes in mass and energy exchange by crops under rising atmospheric CO 2 concentration (C a ) may be affected by N and weather; C, interacts with weather on mass and energy exchange through limitations on latent heat flux imposed by stomatal conductance, which is affected by C a , and aerodynamic conductance, which is affected by weather. We examined the bases for these interactions with the ecosystem model ecosys. Simulation results were tested with energy flux data from a Free Air CO 2 Enrichment (FACE) experiment in which wheat (Triticum aestivum L.) was grown under 548 vs. 363 μmol mol -1 C, and fertilized with 7 vs. 35 g N m -2 . Both model and experimental results indicated that raising C a from 363 to 548 μmol mol -1 reduced midday latent heat fluxes by ca. 50 W m -2 for wheat fertilized with 35 g N m -2 , and by ca. 100 W m -2 for wheat fertilized with only 7 g N m -2 when N deficits developed later in the growing season. These reductions were smaller under low wind speeds (

A free water surface (FWS) constructed wetland was installed at a dairy in Glendale, Arizona, to study the potential of such a wetland to remove nitrogen (N) from wastewater. The study objectives were: (1) to determine N removal from the wastewater, and (2) to evaluate N accumulation in soil and plant tissues. The system consisted of eight cells (70 × 9 × 1.5 m) planted with Typha domingensis, Scirpus validus, and Phragmites australis. The four cells in series were lined with plastic, and the four cells in a parallel series were lined with clay. Cells received approximately 180 m3/d of partially treated dairy effluent. Plant tissues and soil samples were collected above and below ground from 24 locations during one year. Total N removal from wastewater was about 17 percent. Clay-lined cells accumulated more N in the soil and less N in plant biomass compared with plastic lined cells. Plant biomass accounted for approximately 60 percent of total N accumulated in cells with dense plant communities. Ninety percent of accumulated soil N was organic. Total N accumulated in soil reached a maximum (1,100 mg/kg) eight months after the introduction of wastewater.

Past research in the paleoenvironmental subdiscipline of dendro-chemistry has concluded that N concentration variation in tree rings cannot provide information on past conditions of environmental availability of N. The objective of this study was to test wood extraction pretreatments to remove wood extractives and sap, both of which may obscure the environmental signal of N availability in tree rings. Three increment cores were collected from each of six trees (three ponderosa pines and three Douglas-firs). Within each tree, the first core was left untreated (referred to as CONTROL), the second core was extracted for several hours in organic solvents and distilled water (referred to as EXTRACT), and the third core also was extracted but for a total time of 3 d (referred to as 3-DAY). A semimicro Kjeldahl method was used to determine total N on decadal groups of rings. Average N concentration of EXTRACT cores was significantly less than that of CONTROL, and the coefficient of variation of EXTRACT cores also was significantly less than that of CONTROL. Most CONTROL cores showed substantial temporal variation in N concentration related to heartwood and sapwood andlor recently formed rings. In contrast, most EXTRACT cores showed no substantial change in N concentration related to heartwood and sapwood andlor recently formed rings. The 3-DAY cores confirmed, but did not improve upon, results obtained with extraction using the shorter time duration. Thus, pretreating wood by extraction appears to substantially reduce the variation in N concentration of tree rings, which is a necessary first step toward interpreting ring N as an indicator of past environmental N availability.

The mid-day responses of wheat ear CO 2 and water vapour exchange to full-season CO 2 enrichment were investigated using a Free-Air CO 2 Enrichment (FACE) apparatus. Spring wheat [Triticum aestivum (L). cv. Yecora Rojo] was grown in two experiments under ambient and elevated atmospheric CO 2 (C a ) concentrations (approximately 370 μmol mol -1 and 550 μmol mol -1 , respectively) combined first with two irrigation (Irr) schemes (Wet: 100% and Dry: 50% replacement of evapotranspiration) and then with two levels of nitrogen (N) fertilization (High: 350, Low: 70 kg ha -1 N). Blowers were used for C a enrichment. Ambient C a plots were exposed to blower induced winds as well the C a x N but not in the C a x Irr experiment. The net photosynthesis for the ears was increased by 58% and stomatal conductance (g s ) was decreased by 26% due to elevated C a under ample water and N supply when blowers were applied to both C a treatments. The use of blowers in the C a -enriched plots only during the C a x Irr experiment (blower effect) and Low N supply restricted the enhancement of net photosynthesis of the ear due to higher C a . In the latter case, the increase of net photosynthesis of the ear amounted to 26%. The decrease in g s caused by higher C a was not affected by the blower effect and N treatment. The mid-day enhancement of net photosynthesis due to elevated C a was higher for ears than for flag leaves and this effect was most pronounced under ample water and N supply. The contribution of ears to grain filling is therefore likely to increase in higher C a environments in the future. In the comparison between Wet and Dry, the higher C a did not alter the response of net photosynthesis of the ear and g s to Irr. However, C a enrichment increased the drought tolerance of net photosynthesis of the glume and delayed the increase of the awn portion of net photosynthesis of the ear during drought. Therefore, the role of awns for maintaining high net photosynthesis of the ear under drought may decrease when C a increases.

Water x N rate experiments were conducted on subsurface drip-irrigated cauliflower (Brassica olearacea L. var. botrytis L.) during three winter growing seasons in southern Arizona. A range of water and N rates were selected to permit the calculation of appropriate water × N production functions. The objectives were to (i) determine the effects and interactions of irrigation water and N inputs on crop N uptake, residual soil NO 3 -N, N-use efficiency, and unaccounted fertilizer N, and (ii) evaluate agronomic, economic, and environmental production criteria during three growing seasons. Spatial analysis was used to identify overlap of acceptable zones of marketable yield, net return, and unaccounted fertilizer N within each growing season. Acceptable yields and net return were defined as ≥95% of the maximum predicted response within the range of the treatments; acceptable unaccounted fertilizer N was defined as ≤ 40 kg ha -1 . Net returns and aboveground plant biomass N were significantly affected (P < 0.01) by N rate and in 2 yr by irrigation. There were also significant irrigation treatment x N rate interactions for net returns and biomass N. Residual soil NO 3 -N concentrations increased with N rate and decreased with soil water tension (SWT). Average amounts of residual soil NO 3 -N (0-0.9 m) for the highest N rate during the three seasons were 317, 296, and 180 kg ha -1 for the low, medium, and high irrigation treatments, respectively. Unaccounted fertilizer N was significantly affected (P < 0.05) by irrigation treatment, N rate, and irrigation treatment x N rate interactions each year. Overlap of acceptable zones of marketable yields, net returns, and unaccounted N was achieved in one of the three years. The single combination of SWT and N rate that came closest to producing optimal or near-optimal agronomic, economic, and environmental outcomes in all three years was 10 to 12 kPa and 350 to 400 kg N ha -1 .

Production of cauliflower (Brassica olearacea L. var. botrytis L.) in the southwestern U.S. is highly dependent on inputs of water and N fertilizer to achieve optimum yields and quality. Subsurface drip irrigation offers what is likely the ultimate in control of the plant root zone for crop production. However, the water and N-response characteristics of subsurface drip-irrigated cauliflower have not previously been reported. Three field experiments were conducted in southern Arizona in 1993-1996. The objectives were to determine: (i) an optimum range of soil water tension for subsurface drip-irrigated cauliflower, (ii) the effects and interactions of water and N fertilizer on crop yield and quality, and (iii) seasonal and daily N uptake for high-yielding cauliflower. The experiments were randomized complete block factorial with three irrigation regimes (low, medium, high), four N rates (60-600 kg N ha -1 ), and four replications. Irrigation was applied dally to maintain target soil water tensions and all N was applied by fertigation. With respect to marketable yield, curd weight, and curd diameter, the optimum soil water tension was approximately 10 to 12 kPa in this sandy loam soil during the 3 years. Marketable yields across all treatments ranged from 30 Mg ha -1 . Yields and quality were generally more responsive to N rate than to irrigation and showed significant irrigation by N rate interactions during 2 of the 3 years. At equivalent N rates, excessive irrigation generally resulted in lower yields and quality. Cauliflower accumulated up to 250 kg N ha -1 in the aboveground biomass and N-uptake fluxes were as high as 5 kg N ha -1 d -1 at the 12-leaf to folding growth stage.

Agricultural practices may cause contamination of soil and ground water with a combination of organic compounds (pesticides and fuel) and nitrogen fertilizers. In coupled microcosm studies that monitored the mineralization of naphthalene and the nitrification of ammonia, it was observed that the solvent (dichloromethane) used to apply naphthalene to the soil inhibited nitrification, although there was no effect on naphthalene mineralization. Further studies were performed with a series of application solvents: methanol, acetonitrile, trichloromethane, and dichloromethane. Soil and solvent were allowed to equilibrate with ambient air for various times before capping and incubation of microcosms. Results indicated that dichloromethane equilibrated for 5 mins inhibited nitrification for at least 3 weeks relative to the control (water). Acetonitrile and trichloromethane similarly inhibited nitrification. Methanol and dichloromethane equilibrated for 60 mins also significantly delayed nitrification, although to a lesser extent. Inhibition of nitrification was not permanent, and nitrification activity was eventually restored in all systems tested. None of the solvents inhibited mineralization of the added carbon source. These results indicate that special care must be taken to ensure that applications solvents do not affect the activity of sensitive microbial populations, such as the nitrifiers, that may be part of a study.

Evaluation of trickle-irrigated crop production systems should address agronomic, economic, and environmental outcomes. The objectives of this research were to : (i) determine plant N uptake, residual soil inorganic N, unutilized fertilizer N, and unaccounted fertilizer N for subsurface trickle irrigated leaf lettuce (Lactuca sativa L. cv. Waldmann's Green), and (ii) use spatial analysis techniques to simultaneously evaluate agronomic, economic, and environmental production criteria for leaf lettuce within one growing season. Field experiments were conducted using buried trickle irrigation during three winter growing seasons in southern Arizona. Deficient to excessive N (35-300 kg ha -1 ) and target soil water tension (SWT) treatments (12.0-4.0 kPa) were applied in factorial combinations each year. Fertilizer N recovery was determined by the difference method. Spatial analysis of response surfaces was used to determine overlap of zones with acceptable values for marketable yield, net economic return, and unaccounted fertilizer N for leaf lettuce during 1992-1993. Maximum unutilized fertilizer N was 216 kg ha -1 for leaf lettuce, and maximum unaccounted fertilizer N was 149 kg ha -1 . Unutilized fertilizer N and unaccounted fertilizer N increased sharply when adequate N and water rates were exceeded. Spatial analysis of response surfaces for 1992-1993 showed a small region bounded by 6.6 to 7.3 kPa SWT and 238 to 252 kg N ha -1 that would have resulted in >95% of maximum predicted marketable yield and net return while limiting NO 3 -N concentrations in drainage water to ≤10 mg L -1 .

Rising water costs and concerns about groundwater contamination by NO 3 - are forcing growers in arid regions to adopt practices to improve water and N use efficiency. Subsurface trickle irrigation offers the ability to precisely deliver appropriate amounts of water and N to the crop root zone. The objectives of this research were to : (i) determine the optimum level (with respect to marketable yield) of soil water tension for subsurface trickle-irrigated leaf lettuce (Lactuca sativa L. cv. Waldmann's Green), (ii) determine N by water interactions on crop yield and quality, and (iii) determine seasonal patterns of crop N uptake. Three field experiments were conducted during the 1990 to 1993 winter growing seasons on a Casa Grande soil (fine-loamy, mixed, hyperthermic, Typic Natriagid [reclaimed]) in southern Arizona. Deficient to excessive N (35-300 kg ha - 1 ) and target soil water tension (SWT) treatments (12.0-4.0 kPa) were applied in factorial combinations each year. Maximum marketable leaf lettuce yields observed were 54.0 Mg ha -1 . Nitrogen rates associated with maximum yields ranged from 120 to 300 kg ha -1 , and depended on average SWT. Excessive irrigation (5.3 kPa average SWT) resulted in lower yields, head weight, and head length. Marketable yields showed a pronounced water x N interaction, but yield quality (head length and weight) did not. Maximum N flux was 4.3 kg ha -1 d -1 , and an average of 75% of total N accumulation occurred in the 38 d prior to harvest. Results suggest that the soil water tension at 0.3-m depth should be maintained at 6 to 7 kPa for optimum yields of trickle-irrigated leaf lettuce.

Nitrogen fertilizer use is essential for optimizing yield of irrigated malting barley (Hordeum vulgare L.) but must be managed carefully to achieve optimum grain protein concentrations demanded by the malting industry. Development of tissue tests, applicable for growing conditions in the desert Southwest, would be of benefit to growers for optimizing yield and grain protein of irrigated malting barley. Field experiments were conducted with two cultivars of malting barley [Morex (six row) and Crystal (two row)] under irrigated conditions in southern Arizona. The objectives were to (i) determine yield and grain protein response to N applications, (ii) determine the relationship between lower-stem tissue and sap NO 3 -N, and (iii) develop lower-stem and sap NO 3 test guidelines for N management in malting barley. Yields ≥90% of maximum relative yield and grain protein concentrations acceptable for malting were achieved at N rates (kg ha -1 ) of 242 to 269 (1997-1998) and 205 to 269 (1998-1999) for Morex and 162 to 178 (1997-1998) and 166 to 181 (1998-1999) for Crystal. Stem and sap NO 3 -N were significantly correlated in both cultivars, with r 2 values of 0.72 in Morex and 0.82 in Crystal. We propose that, to achieve acceptable grain yield and protein, lower-stem sap NO 3 -N in malting barley should be no less than 300, 180, and 120 mg L -1 and dry stem tissue NO 3 -N should be no less than 3000, 1000, and 800 mg kg -1 at Feekes growth stages 3, 7, and 10, respectively.