Typic Torrifluvent Research Articles

Effect of Sulfur Source on Sulfur Oxidation

AbstractThe rate of elemental sulfur (So) oxidation in soils may be affected by the source of So. This study was conducted to determine the effect of So source on So oxidation. Liquid culture studies with Thiobacillus thiooxidans and T. thioparus, laboratory incubations with a Holloman soil (loamy, gypsic, thermic, shallow Typic Torriorthent) and a Belen soil (clayey over loamy, montmorillonitic [calcareous], thermic Typic Torrifluvent), and a field study on the Belen soil were conducted. Periodic measurements included pH as a measure of So oxidation to H2SO4, electrical conductivity (EC) as a measure of dissolution of CaCO3 from H2SO4 production, and available Fe, Zn, P, and SO4 at the end of soil experiments as a measure of So‐oxidation effects on nutrient availability. The So sources included pure So (Sp), Wettable S (Sw), flowable So (Sf), and Disper‐Sul So (Sd). In liquid culture, Sw, Sf, and Sd inhibited or slowed So oxidation, compared with Sp, suggesting an ingredient of the commercial So sources was responsible for oxidation inhibition. Oxidation of Sw, Sf, and Sd were similar to Sp oxidation in laboratory soil incubations and in the field. Results indicate that the So source is not the cause of slow So oxidation in some New Mexico soils. Chemoautotrophic So oxidizers were present in unamended soils and their numbers increased in So‐amended soils. Although So amendment (25 g So kg−1) in the field decreased pH approximately 0.5 unit and increased SO4 tenfold, So amendment did not increase available Fe, Zn, or P. The slow rate of So oxidation in some New Mexico soils and failure of So amendment to increase nutrient levels are attributed to the buffering capacity of the calcareous soils.

Virus Transport and Survival in Saturated and Unsaturated Flow through Soil Columns

AbstractWater with entrained disease‐causing virus entering soil normally passes through water‐saturated and unsaturated regions before reaching the groundwater. The effects of saturated and unsaturated flow on the survival and transport of a virus, MS‐2 bacteriophage, were compared. The viruses were added to well water and applied to soil columns 0.052 m in diameter and 1.05 m long. The soil material was Vint loamy fine sand (a sandy, mixed, hyperthermic Typic Torrifluvent) mixed with recent alluvium. Samples of the soil water were taken daily at 0.20, 0.40, and 0.80 m depths through porous stainless steel samplers and at 1.05 m from the percolate leaving the column. For saturated flow the virus concentrations reached the influent concentration in less than two pore volumes (PV). For unsaturated flow the concentrations remained at levels much lower than the influent, ranging from 27% of inflow at 0.20 m (18 PV) to 5% at 1.05 m (3.3 PV). At the end of the experiments soil samples from each depth were assayed to determine virus adsorption to the soil. The average distribution coefficient of the unsaturated columns, 0.27, indicates very little adsorption. The number balance showed that only 39% of the unsaturated flow virus were accounted for. It appears that under unsaturated flow conditions enhanced inactivation of this virus occurs.

Salinity Effects on Emergence, Vegetative Growth, and Seed Yield of Guar

AbstractGuar [Cyamopsis tetragonoloba (L.) Taub] seed is an important source of galactomannan gum used in food and industrial products. Increased demand and an insufficient domestic supply has led to an increased interest in this crop in the semi‐arid western USA where many soils are, or have the potential to become, highly saline. This study was conducted to determine the effect of soil salinity on vegetative growth and seed yield of two cultivars, 'Kinman' and 'Esser,' grown under field conditions. Six salinity treatments were imposed on a Holtville silty clay [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCl2 (1:1 by weight). Electrical conductivities of the irrigation waters were 1.3, 2.5, 5.0, 7.4,10.0, and 12.4 dS/m during the 1st yr, and 1.2, 2.5, 4.5, 5.5, 6.5, and 7.5 dS/m during the 2nd yr. Seed yield of both cultivars was unaffected by soil salinity up to 8.8 dS/m (mean electrical conductivity of the saturated‐soil extracts in the rootzone). Each unit increase in salinity above 8.8 dS/m reduced seed yield by 17%, which places guar in the moderately tolerant category for seed production. Reduction in the number of pods per plant and weight per seed were the primary factors contributing to reduced yields. Vegetative growth was decreased 9.6% for each unit increase in salinity above 4.9 dS/m. Plant emergence was determined in greenhouse sand cultures with irrigation waters of 0.8, 4.4, 8.5,11.3,15.7, and 18.8 dS/m. Emergence was unaffected by salt levels up to 8.5 dS/m; greater levels delayed but did not significantly reduce the percent emerged.

Comparative effects of chemical amendments on salt and NA leaching

Efficiency of sodic soil reclamation is thought to vary with types of chemicals used. This study examined the effects of five inorganic (H2SO4, CaCl2 · 2H2O, CaSO4 · 2H2O, FeSO4, Al2(SO4)3) and two organic compounds (polyacrylamide, and trihydroxy glutaric acid) on the rate and the extent of salt and Na leaching in moderately Na-affected saline soils: Saneli silty clay loam (Vertic Torrifluvents, ESP=17.5%) and Glendale silty clay (Typic Torrifluvents, ESP=13.5%). Air-dry soil samples (<2mm) were packed in columns, and chemicals, except H2SO4, were incorporated into the surface 5 cm of the soils, and in selected cases, to 30 cm. H2SO4 was surface-applied. Application rates of the inorganic chemicals were 3.57 and 10.7 mmol(+) kg-1 (2.5 and 7.5 Mg ha-1 in gypsum equivalent weight) in the silty clay loam, and 8 and 24 mmol(+) kg-1 in the silty clay, and the organic compounds were applied at rates of less than 620 kg ha-1. The soils were then leached with simulated Rio Grande water (EC = 1.1 dS m-1, SAR = 3.5) under continuous ponding. The tested inorganic compounds removed approximately equivalent amounts of exchangeable Na after approximately 35 cm of water application. However, the rate of water percolation (consequently the rate of salt leaching) from CaCl2 treated columns, became progressively slow after about 20 cm of water intake. The combined effect of rapid electrolyte leaching and insufficient replacement of Na in the surface layer seemed to be responsible for the flow reduction. Gypsum and H2SO4 treatments provided lower ratios of sodicity to salinity in percolating solutions and relatively uniform hydraulic gradients throughout the soil depth. Incorporation of chemicals to the surface 30 cm did not alter performance, except in CaCl2 treatments where water intake rates became even slower. The tested organic amendments improved initial water infiltration, but neither increased subsequent percolation rates nor improved salt and Na leaching. The fastest reclamation may be attained when chemicals are chosen and applied to yield an electrolyte concentration that is high enough to overcome Na effects at any depth of soil profiles throughout the leaching period.

Wheat responds to sewage sludge as fertilizer in an arid enviroment

Experiments were conducted in Avra Valley, Arizona to compare plant growth, hay yield, grain yield, straw yield, and livestock feeding qualities of wheat (Triticum durum Desf.) fertilized with sewage sludge with that of wheat fertilized with inorganic nitrogen (N). The wheat was grown on a sandy loam soil (of the coarse loamy mixed typic torrifluvents series) and fertilized with recommended rates of inorganic N and recommended rates of plant-available N from anaerobically digested liquid sewage sludge. Fertilization with sewage sludge increased number of days from planting to heading, plant height, and tillering. The low sludge rate and the inorganic N treatment produced similar yields of hay, grain, and straw. The high sludge rate produced the most hay and straw; however, it did not result in a significant increase in grain yield. Wheat hay, grain, and straw grown with sewage sludge and inorganic N were similar in livestock feeding qualities. Heavy metal concentratons in wheat hay, grain, and straw were low in all fertilizer treatments. Cadmium and Nickel levels were below detectable limits. When wheat was grown to maturity, more heavy metals accumulated in the grain than in the straw.

Salinity Effects on Rye Grain Yield, Quality, Vegetative Growth, and Emergence

AbstractAlthough current rye (Secale cereale L.) grain production is concentrated mainly in the northern half of the USA and Canada, some rye grain is grown in the arid southwest. Soils in this area are, or have the potential to become, highly saline from the application of saline irrigation water. Since there is nearly a complete lack of information about the response of rye grown under saline conditions, a 2‐yr field plot study was conducted. Six salinity treatments were imposed on a Holtville silty clay (clayey over loamy, montmorillonitic [calcareous], hyperthermic Typic Torrifluvent) by irrigating with Colorado River water artificially salinized with NaCl and CaCl2 (1:1 by weight). Electrical conductivities of the irrigation waters were 1.1, 4.0, 8.0, 12.1, 16.0, and 20.1 dS m−1 the first year, and 1.1, 3.9, 7.5, 11.6, 15.6, and 19.8 dS m−1 the second year. Grain yield and vegetative growth were measured. Relative grain yield of two cultivars, Maton and Bonel, was unaffected up to a soil salinity of 11.4 dS m−1 (electrical conductivity of the saturation extract;κe). Each unit increase in salinity above 11.4 dS m−1 reduced yield by 10.8%. These results place rye in the salt‐tolerant category. Yield reduction was attributed primarily to reduced spike weight and individual seed weight rather than spike number. Bread quality decreased slightly with increasing levels of salinity. Straw yield was more sensitive to salinity than was grain yield. Plant emergence was determined in greenhouse sand cultures. Both cultivars were slightly less salt tolerant during plant emergence than during subsequent stages of growth.

Water Uptake by Cotton Roots during Fruit Filling in Relation to Irrigation Frequency

Yield of irrigated cotton (Gossypium hirsutum L.) increases as the interval between water applications is decreased, even if the total amount of water applied is unchanged. Experiments were undertaken to compare season‐long water relations of high‐frequency dripirrigated cotton (I‐ to 2‐d intervals) to cotton irrigated at approximately 2‐wk intervals. The crop was grown at two locations in central Arizona on a Mohall sandy loam (fine‐loamy, mixed, hyperthermic Typic Haplargid) and an Avondale clay loam (fine‐loamy, mixed, hyperthermic Typic Torrifluvent) soils. In 2‐yr trials at each location, irrigation frequency had inconsistent effects on midday leaf water potential (ψw) during vegetative growth. When the crop developed a heavy fruit load, however, ψw of plants on the longer cycles was much lower than that of drip‐irrigated plants, even after irrigation when ample soil moisture should have been available. Plant hydraulic conductances, estimated from regressions of single‐leaf transpiration rate against ψw, were high in both treatments early in the season. Hydraulic conductance decreased greatly during fruiting in plants on long irrigation cycles but less so in drip‐irrigated plants. Late in the season, after fruit maturation and daring plant regrowth, conductances were again high and similar in the two treatments. The results imply that during heavy fruiting, mild water stress associated with long irrigation cycles triggers deterioration of the root system that is very slow to be reversed. High‐frequency drip irrigation, by preventing cyclical stress, apparently minimized this deterioration during fruit filling.

Potato Leafhopper‐Induced Injury on Growth and Development of Alfalfa

Yield of irrigated cotton (Gossypium hirsutum L.) increases as the interval between water applications is decreased, even if the total amount of water applied is unchanged. Experiments were undertaken to compare season‐long water relations of high‐frequency dripirrigated cotton (I‐ to 2‐d intervals) to cotton irrigated at approximately 2‐wk intervals. The crop was grown at two locations in central Arizona on a Mohall sandy loam (fine‐loamy, mixed, hyperthermic Typic Haplargid) and an Avondale clay loam (fine‐loamy, mixed, hyperthermic Typic Torrifluvent) soils. In 2‐yr trials at each location, irrigation frequency had inconsistent effects on midday leaf water potential (ψw) during vegetative growth. When the crop developed a heavy fruit load, however, ψw of plants on the longer cycles was much lower than that of drip‐irrigated plants, even after irrigation when ample soil moisture should have been available. Plant hydraulic conductances, estimated from regressions of single‐leaf transpiration rate against ψw, were high in both treatments early in the season. Hydraulic conductance decreased greatly during fruiting in plants on long irrigation cycles but less so in drip‐irrigated plants. Late in the season, after fruit maturation and daring plant regrowth, conductances were again high and similar in the two treatments. The results imply that during heavy fruiting, mild water stress associated with long irrigation cycles triggers deterioration of the root system that is very slow to be reversed. High‐frequency drip irrigation, by preventing cyclical stress, apparently minimized this deterioration during fruit filling.

Planting Seed Density in Relation to Cotton Emergence and Yield

AbstractCotton (Gossypium hirsutum L.) planting seed density has been related to seedling emergence and vigor, although its effects on yield are not clearly understood. Seed lots of the cultivar ‘DP90’ were separated into four density classes using a gravity separation table. These seed classes were evaluated along with an undivided seed sample and a sample from processed seed selected for commercial use. The seed classes were planted at three planting rates in seven tests conducted from 1983 to 1985 at Maricopa, Marana, and Safford, AZ. The soils at these locations are Typic Camborthids, Thermic Torrifluvents, and Typic Torrifluvents, respectively. The lowest density seed had significantly lower standard and cold germination test results; however, there were no differences among the other five seed classes in 2 of the 3 yr. Field emergence of the highest density seed was significantly greater than that of the other density classes for the seven tests combined, and was significantly lower for the lowest density seed. Lint yields produced by plants from the highest density seed were significantly greater than those of the four other seed classes, and the lowest density seed produced significantly lower yields. There were no significant interactions between planting seed density and planting rate for yield. The results indicate that cotton planting seed quality could be improved slightly by selecting higher density seed

Effect of Salinity on Grain Yield and Quality, Vegetative Growth, and Germination of Triticale

AbstractDevelopment of high yielding triticale (X Triticosecale Wittmack) cultivars may promote an increased acreage of this crop on irrigated soils in the western United States. Often these soils are, or have the potential to become, highly saline. Because of the lack of information on salinity effects on vegetative growth and seed yield of triticale, the salt tolerance of two cultivars (Beaguelita ‘s’ and Cananea 79) was determined in a 2‐yr field plot study. Six salinity treatments were imposed on a Holtville clay [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCl2, (1:1 by weight). Electrical conductivities of the irrigation waters were 1.8,2.6, 5.1, 7.5,9.6, and 12.2 dS/m the first year, and 1.4, 3.9, 7.9, 12.0,16.0, and 20.3 dS/m the second year. Grain yield, vegetative growth, and germination were measured. Relative grain yield for both cultivars was unaffected by soil salinity up to 7.3 dS/m (electrical conductivity of the saturated‐soil extracts in the rootzone). Each unit increase in salinity above 7.3 dS/m reduced grain yield by 2.8%. These results place triticale in the salt‐tolerant category. Yield reduction resulted primarily from a reduction in spike number rather than from lower weight per spike or lower weight per individual seed. Salinity reduced vegetative growth less than grain yield in Cananea 79 but more in Beaguelita ‘s’. Both cultivars were slightly less salt tolerant at germination than they were after the three‐leaf stage of growth.

Soil Carbon Dioxide Distribution and Flux within the Open‐top Chamber

AbstractOpen‐top chamber use for exposing plants to various levels of CO2 and pollutant gases is increasing in field studies. In making a C balance of cotton [Gossypium hirsutum (L.) ‘Deltapine‐61’] for such a system, soil CO2 fluxes were observed to be significantly greater outside than inside the chamber. To find the cause, CO2 concentration was measured in the soil profile from 5‐ to 60‐cm depths of an Avondale clay loam [fine‐loamy, mixed (calcareous), hyperthermic Typic Torrifluvent]. The soil CO2 contents at the various depths sampled outside the chamber were higher than those inside the chamber. The differences in concentration were observable within 2 wk after the blower used to pass ambient of CO2‐enriched air through the chamber was turned on. The largest differences were present approximately 16 wk after the system had been in operation. Approximately 30 d was required for the soil CO2 levels inside and outside the chamber to become similar after the blower was turned off. Soil water content was not a factor causing this difference because it was nearly equal at both sites. Pressure differentials inside the growth chamber resulting from the blower operation could lead to a decrease in soil CO2 concentration and fluxes measured using the closed chamber technique.

Previous Sludge Addition Effects on Nitrogen Mineralization in Freshly Amended Soil

AbstractAn experiment was conducted to determine the effects of previous sludge additions on N mineralization in a freshly amended soil. A secondary objective was to further delineate statistical models of N mineralization potential (No) and the mineralization rate constants k and h. The Glendale clay soil (fine‐silty, mixed thermic, Typic Torrifluvents), with either no previous sludge amendment or sludge applied at the rate of 67.3 Mg ha−1 in 1982 or 1983 in the field, was freshly amended with 30 g kg−1 of gamma irradiated, dried, anaerobically digested sewage sludge in 1985. Triplicate samples of each soil (unamended, amended in 1982, and amended in 1983) and each sludge treatment (no amendment and freshly amended) were incubated aerobically for 16 wk at 0.01‐MPa moisture potential and 35 °C. Periodically the soils were leached with 0.01 M CaCl2, and the leachate was analyzed for inorganic and organic N. Previous sludge amendment had no effect on the mineralization of resh sludge. Soils previously amended in 1982 and 1983 leached 56 to 60 mg kg−1 more NO‐3 + NO‐2 than unamended or freshly amended soils never amended with sludge. Total organic N mineralization averaged 65.4% and was independent of soil amendment history or fresh sludge amendment. Values of No, k, and h were estimated by nonlinear least squares for several nonlinear models. The best fit of the data resulted from modeling N mineralization as the sum of an exponential equation (of the rapidly decaying organic N fraction) and a constant (of the slowly decaying organic N fraction). Mineralization curves failed to flatten after 16 wk, suggesting that the experiment should have run longer before a two‐exponential equation would have satisfactorily explained the data.

Irrigation and Plant Spacing Effects on Seed Production of Buffalo and Coyote Gourds

AbstractBuffalo gourd (Cucurbita foefidissima HBK) and coyote gourd (Cucurbita digitata Gray) are xerophytic perennial cucurbits with potential as oilseed or starch crops for arid and semiarid lands. This study investigated irrigation and plant spacing effects on growth, water requirements, and oilseed production of these species. Irrigation of first‐season buffalo gourds planted in 1981 at a 610‐m elevation site on Pima clay loam [fine‐silty, mixed (calcareous) thermic Typic Torrifluvent], and irrigation and plant spacing were evaluated on first‐season buffalo and coyote gourds at a 360‐m site in 1983 on Casa Grande sandy loam (fine‐loamy, mixed, hyperthermic Typic Natrargid) and Trix clay‐clay loam [fine‐loamy, mixed (calcareous), hyperthermic Typic Torrifluvent], respectively. Irrigation and plant spacing were evaluated on second‐season buffalo gourds planted in 1983. Irrigation did not affect first‐season buffalo gourd yields. Second‐season yields were reduced by irrigating when the available soil water was 75% depleted (I2) compared to irrigating when soil water was 50% depleted (I1). Coyote gourd yields were reduced by the I2 treatment in 1983 but not in 1984. Consumptive water use for first season buffalo gourds in the I1 treatment at the 610‐ and 360‐m sites was 870 and 645 mm, respectively. Consumptive water use was similar for coyote and buffalo gourds at the 360‐m site. In the first season, these species derived up to 50% of water used from the top 0.4 m of soil, and extracted water to a depth of at least 2.6 m. Irrigation did not affect water‐use efficiency (WUE) of either species. Buffalo gourds had higher WUE in the second season (0.09 kg seed m−3 water) than the first season (0.04 kg m−3). Plant spacings of 0.25 to 2 m in 1‐m spaced rows had no effect on first‐season yield in 1983, but in 1984 a quadratic relationship indicated that the closest and widest spacings reduced yields. Coyote gourd consistently outyielded buffalo gourd at the 360‐m site. Although these gourd species have promising water use characteristics for arid lands agriculture, the low seed yields of the cultivars currently available appear to limit their potential as oilseed crops.

Effect of ammonium fertilizer on NH3 loss and Ca, Mg, ammonium and nitrate content in a calcareous soil solution

This study examined the effects of NH inf4 + fertilizers [(NH4)2SO4, (NH4)2HPO4, CO(NH2)2, NH4OH, and NH4NO3] on NH3 loss and the quantity of Ca + Mg, NH inf4 + and NO inf3 sup− in the solution of a calcareous soil (Harkey sicl, Typic Torrifluvent). Various NH4 fertilizers applied at a depth of 5 cm in the soil produced differing NH3 loss characteristics. Applying (NH4)2SO4 (AS) resulted in high volatile NH3 losses as compared with NH4OH (AH) and (NH4)2CO3 (AC). The AS treatment formed an equal molar amount of CaSO4, which increased the mobility of ammonium, while AH and AC treatments caused Ca precipitation and decreased ammonium mobility. Leaching the AS system before NH3 loss could occur resulted in the most rapid nitrification rate. Lower nitrification rates were found with AH and AC than AS under the same conditions. Surface placement of NH4 fertilizers resulted in variable leachate contents of Ca + Mg. Ammonium sulfate reacted with CaCO3 either to solubilize some Ca + Mg or simply to replace exchangeable Ca + Mg with NH4, while AH, AC, and (NH4)2HPO4 (DAP) precipitated essentially an equivalent molar amount of soluble and adsorbed Ca + Mg. Use of NH4NO3, which does not form an insoluble calcium precipitate, resulted in the leaching of an equivalent molar amount of exchangeable Ca + Mg from the Harkey soil.

Crop‐water Production Functions for Sweet Corn and Cotton Irrigated with Saline Waters

AbstractThe effect of irrigation water quality (salinity) and quantity on the yields of sweet corn (Zea mays cv. Jubilee) and cotton Gossypium hirsutum L. cv. Acala SJ‐2) was studied in a sandy loam (Typic Torrifluvent) soil. For each of the irrigation water salinities of Co = 1.8, 3.6 and 6.7 dS/m (for corn) and Co = 3.6, 6.7, and 10.5 dS/m (for cotton), 10 amounts of irrigation water (Q) ranging from 0.15 to 2.7 times the class A pan evaporation (Eo) were applied via trickle irrigation. Root zone soil‐water matric potential, water content, and salinity were monitored, and corn and cotton yield components were measured. Time‐averaged root zone soil water content (θ) and soil salinity (EC), as well as crop yield components (Y) were affected by both Q and Co. Results of the analyses of the crop‐water production functions suggest that increasing the amount of irrigation water may compensate only in part for the adverse effects of the salinity of the irrigation water. For corn, using irrigation water of Co = 3.6 and 6.7 dS/m, maximum ear yields were reduced by 8 and 27%, respectively, relative to the maximum ear yield obtained using water of 1.8 dS/m. For cotton, using irrigation water of Co = 6.7 and 10.5 dS/m, maximum seed cotton yields were reduced by 6.5 and 30%, respectively, relative to the maximum seed cotton yield obtained using water of 3.6 dS/m. Analysis of the Y(θ, EC) relationship for each of the corn and the cotton yield components suggested that, due to the mutual effect of θ and EC on Y, the crop response to salinity curve is affected by θ and, in general, should be described by a nonlinear concave expression rather than by the piecewise linear expression of Maas and Hoffman (1977).

Plant Water Relations, Photosynthesis, and Rubber Content of Young Guayule Plants during Water Stress1

AbstractGuayule (Parthenium argentatum Gray, cv. N565 II), a drought tolerant, rubber‐producing shrub native to the desert Southwest, was grown in field plots at Phoenix, AZ, in an Avondale loam soil [fine, loamy, mixed (calcareous), hyperthermic Typic Torrifluvent] in well‐watered and drought conditions. The purpose of the investigation was to characterize the relationships between plant water relations, photosynthesis, and rubber content during drought stress to improve water management practices. The drought treatment lasted 70 days (29 May–5 Aug. 1986) during which the soil moisture content gradually declined from 340 to 165 mm in the top 1.1 m of soil. The well‐watered plots were maintained at greater than 260 mm soil moisture per 1.1 m of soil. Values for psychrometric measurement of water potential of the stressed plants declined to −3.0 MPa, 1.2 MPa less than the well‐watered plants, while maintaining approximately equal and positive pressure potential. This suggests an important role for osmotic adjustment in the drought tolerance of guayule. Net photosynthesis in both treatments steadily declined from about 10.0 to 3.5 µMol m−2 s−1 during the experiment, but with no apparent inhibition due to drought stress. Rubber content increased over fivefold in the stressed plants (from 0.4 to 2.1%) and doubled in the well‐watered plants (from 0.4 to 0.8%) over the course of the experiment. However, the stress treatment reduced final plant size, based on plant height and width measurements, by approximately one‐third compared to the well‐watered treatment. Controlled periods of stress should be investigated as a potential management tool to increase rubber content as well as reduce irrigation water requirements.

Partitioning Yield Reduction from Early Cotton Planting1

Delayed cotton (Gossypium spp.) planting generally reduces lint yield because it reduces the length of the growing season. Planting cotton too early also can reduce lint yield. Most growers believe that reduced yield with early planting is caused by reduced stand. Previous research suggested that low temperature during germination and early seedling growth may reduce lint yield regardless of stand. This study attempts to clarify low temperature effects on lint yield by partitioning cotton lint yield reduction from early planting into the effects from reduced stand and other factors. Soils were Typic Torrifluvents. Thermic Torrilluvents, and Anthropic Torrifluvents. Upland cotton (Gossypium hirsutum L.) had significantly (P &lt; 0.05) reduced lint yield from early planting in five tests. American pima cotton (G. barbadense L.) grown in four of the tests had smaller, nonsignificant lint yield decreases from early planting in three of the tests and higher lint yield from early planting in the fourth test. Early planted cotton generally was shorter. A comparison of upland cotton lint yields, using adjustment by regression analyses with plant population, indicated that something other than plant population, presumably low temperature, caused approximately 100, 94, 66, 22, and 0 % of the lint reduction from early planting in five analyses. Thus physiological and morphological effects of low temperatures early in the cotton planting season often may contribute as much to reduced lint yield as does reduced stand.

Moisture Stress Effects on the Yield and Water Use of Sorghum Hybrids and their Parents*

AbstractLittle is known of the relationship between hybrids and parental material with respect to water use and drought resistance. Responses of sorghum (Sorghum bicolor [L.] Moench) F1 hybrids to moisture deficits are partially determined by parental material. The yield and water use of six sorghum hybrids and their respective male and female parents were evaluated under stressed and well irrigated conditions during 1980 and 1981 at Tucson, Arizona. The soil was Comoro loamy sand (coarse‐loamy, mixed, calcareous, thermic typic Torrifluvent) with an average available soil moisture of 16 % at field capacity.Changes in soil moisture were monitored semi‐weekly by neutron modulation. Meteorological data were collected daily. The 1980 season had higher maximum temperatures and pan evaporation than the 1981 season. Differences in cumulative water use among entries were apparent within the same water treatments during 1981. Mean cumulative evapotranspiration (ET) for the stressed treatment was 248 and 281 mm for 1980 and 1981, respectively, and ET under well irrigated conditions was 419 and 528 mm for 1980 and 1981, respectively.Hybrids produced greater grain yield than their parents under both water treatments. This was due to greater seed number for hybrids. Seed numbers were more stable for hybrids over both treatments than for parents. Hybrids four and seven had the greatest grain yield in 1980 and 1981, respectively, under stressed conditions. Water use efficiency (WUE) was significantly different within water treatments but was not so between the irrigated and stressed treatments. Hybrids WUE was generally greater than that of parents except for hybrid five under irrigated conditions in 1981. Hybrids with WUE and stable yields were not necessarily reflective of parental material under stressed and non‐stressed environments.

Soil‐Dependent Spectral Response in a Developing Plant Canopy1

AbstractA major problem in the use of remote sensing techniques to assess plant biomass and condition over incomplete canopies concerns the soil background contribution toward measured spectral response. An understanding of this soil signal is essential to better relate canopy spectra with plant properties. An interactive, plant‐soil radiant flux model was developed to separate spectral variations associated with soil background from those attributable to vegetation. Field measured spectra taken over n developing cotton (Gossypium hirsutum L.) canopy with four soil types (Cumulic Cryoboroll, Typic Torrifluvent, Ustollic Haplargid, and Typic Calciorthid) alternately inserted underneath were decomposed into soil and vegetation spectra by utilizing the model in a principal component analysis. The soil component included all radiation penetrating the canopy and interacting with the underlying soil. The vegetation component represented all radiation reflected directly from the plant cover with no soil interaction. The soil component was found to resemble the spectral response of green vegetation due to the scattering and transmittance properties of the overlying plant canopy. Results show how the soil signal mixes into various vegetation indices inhibiting reliable vegetation discrimination. The potential improvements in vegetation analysis that can result from filtering soil background response from plant‐canopy spectra are also discussed.

Lettuce Yield‐Irrigation Water Quality and Quantity Relationships in a Gypsiferous Desert Soil1

AbstractEvaluation of the possibility of utilizing marginal soils and saline waters for agricultural production is essential for the development of arid zones. The effect of irrigation water quality (salinity) and quantity on the yield of lettuce (Lactuca saliva var. ‘Iceberg’) was studied in a gypsiferous desert soil (Typic Torrifluvent). Irrigation water volume (Q) ranging from 0.37 to 1.3, 0.6 to 1.6, and 0.7 to 2.4 times the Class A pan evaporation (Eo) for the irrigation water salinities of Ciw = 1.7, 3.1, and 4.7 dS/m, respectively, were applied via trickle irrigation. Root zone soil water pressure potential and salinity were monitored and lettuce yield was measured. Seasonal average soil water content (θ̅) was affected by irrigation water volume but not by quality (salinity) whereas seasonal average soil water salinity (E̅C̅) and lettuce yield (Y) were affected by both quality and quantity of the irrigation water. For the different ranges of Q associated with the different irrigation waters, θ̅ was increased by 30, 44, and 94%, EC was decreased by 20, 21, and 18%, and Y was increased by 120, 71, and 55% for Ciw = 1.7, 3.1, and 4.7 dS/m, respectively. Curvelinear salt tolerance functions were found to be dependent on the volume of irrigation water, approaching a piecewise linear function when relatively large volumes of irrigation water (Q/Eo &gt; 1) were applied. The increase in irrigation volume compensated only in part for the adverse effect of the irrigation water salinity. Maximum yields obtained using the more saline waters are 6.5 and 20.7% smaller for Ciw = 3.1 and 4.7 dS/m, respectively, relative to yield obtained using Ciw =1.7 dS/m.