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The fixing of phosphorus (P) added to calcareous soils is rapid but can be reduced by applying organic sources. The objectives of this study were to measure in the field the residual NaHCO3‐extractable P resulting from manure applications at high rates and to contrast the NaHCO3‐extractable P levels for manure vs. inorganic P fertilizers. When inorganic P was applied at 490 kg/ha for each of 2 years the NaHCO3‐extractable P was increased from 16 to 31 ppm at the 0‐ to 30‐cm depth. The application of 98 kg/ha of P as triple superphosphate each of 2 years applied just before planting lettuce (September‐October) was as effective for increasing NaHCO3‐extractable P during the lettuce‐growing season (November 1976) as applying 490 kg/ha of P in May or June each of 2 years. High rates of P (5,344 kg/ha) applied from manure sources (treatment 720E) resulted in high levels of NaHCO3‐extractable P up to 377 ppm. Total application of more than 360 metric tons/ha of manure (2,672 kg P/ha) resulted in movement of P to the 30‐ to 60‐cm depth. The increased level of NaHCO3‐extractable P from a manure application (treatment 360B) was still evident in the 0‐ to 30‐cm depth 6 years after manure application had ceased. The application of 392 kg P/ha as triple superphosphate for each of 2 years increased the NaHCO3‐extractable P over the check by 11 ppm (November 1976). In contrast, the application of 334 kg P/ha from applied manure (treatment 180B) each of 2 years increased the NaHCO3‐extractable P over the check (after harvest in 1972) by 100 ppm.

Alfalfa (Medicago sativaL.) was grown under two zone production systems (no harvest traffic) (i) preplant compaction and (ii) no preplant compaction and compared to two systems where traffic was applied (i) to 100% of the area during each harvest and (ii) to lanes simulating the traffic a grower would apply during harvest. The experiment was done in a semiarid area under irrigation on a Wasco sandy loam (coarse‐loamy, mixed, nonacid, thermic Xeric Torriorthent), which is easily compacted. Without traffic the soil settled to a bulk density of 1.6 to 1.70 Mg m−3. Traffic increased the bulk density to the 1.8 to 1.9 Mg m−3range. Increases in bulk density at the 0.05‐ and 0.15‐m depths occurred only during the first five passes of traffic, but 10 passes were required to reach a stable bulk density at depths of 0.25 to 0.5 m. Traffic similar to what a grower would apply reduced yields by 10% compared with no traffic. Compacting 100% of the soil surface after each harvest reduced yields 17% compared with no traffic.

Effect of salinity on rice (Oryza sativaL.) after the boot stage has been controversial in the literature. Some authors maintain that rice is sensitive to salt at flowering, whereas others have found no evidence to support these views. The present greenhouse study evaluates the interaction after the boot stage of salinity, soil texture, and rate of drainage on rice development. Breeding line IV 213 was transplanted into 11‐liter pots filled with either silty clay or silt loam soil and irrigated with Colorado river water, S1(EC = 1.4 mmho/cm), until after the boot stage. Then pots were irrigated until harvest with S1, S2(EC = 4.0 mmho/cm), and S3(EC = 8.0 mmho/cm) under the following three drainage rates from the bottom of the pots: 0, D0; 100, D1; and 200 ml/day, D2. The pots soils were always submerged and treatment water was added to replenish water lost by ET and internal draining. Soil and plant analyses showed that: Average salinities in the root zone were 2 to 4 times the salinities of the respective irrigation waters. In general, salinities increased with plant development and with decreasing rate of drainage. Salt components added to Colorado river water increased in both straw and grain without effect on yield.Mature grain yield of S1and S2did not differ significantly; average grain yield of S3was 84% of S1More reduction in yield would be expected if rice was sensitive to salt after the boot stage.Average grain yield on silty clay soil was 16% higher than on silt loam soil.Neither straw yield nor ratio of aborted to mature grain differed significantly among the various treatments. Also rate of drainage had no appreciable effect on concentration of soluble Fe, Mn, or dissolved O2in the soil solution. The unexpected effect of rate of drainage was probably due to frequent replenishment with fresh irrigation water. Average salinities in the root zone were 2 to 4 times the salinities of the respective irrigation waters. In general, salinities increased with plant development and with decreasing rate of drainage. Salt components added to Colorado river water increased in both straw and grain without effect on yield. Mature grain yield of S1and S2did not differ significantly; average grain yield of S3was 84% of S1More reduction in yield would be expected if rice was sensitive to salt after the boot stage. Average grain yield on silty clay soil was 16% higher than on silt loam soil. Neither straw yield nor ratio of aborted to mature grain differed significantly among the various treatments. Also rate of drainage had no appreciable effect on concentration of soluble Fe, Mn, or dissolved O2in the soil solution. The unexpected effect of rate of drainage was probably due to frequent replenishment with fresh irrigation water.

Losses of alfalfa (Medicago sativaL.) occur under the combination of high summer temperatures and clay soils. This paper examines the relationship between these losses and soil temperature, texture, and aeration. The study consisted of short tests (one irrigation) and long‐term experiments (2.5 yr) in the field, and gas exchange experiments in a greenhouse. The design for the field experiments was a randomized block with four replications for the short‐term experiments and three replications for the long‐term experiment. It was necessary to flood 56 h (silty clay soil under high temperatures) to damage alfalfa in the field. Root damage was only 1% in a clay loam soil compared to 10% in a silty clay soil (56‐h flooding time and high temperature). Sufficient water could not be applied in the long term experiment to the alfalfa to leach salts (84% Epan treatment) without severe losses in stand. Long flooding times (96 h) at medium temperatures (maximum air temperature 32°C) did not result in root damage to the alfalfa. Oxygen deficiency, not ethylene toxicity, seemed to be the problem when alfalfa was flooded. Ethylene levels in the field were low and symptoms of toxicity were not observed. In the greenhouse, no damage to alfalfa occurred until O2fell to 0.01 L/L at high temperatures. Results of this experiment indicate that there is a high probability of damage to grower fields when O2stress under high temperature extends over many irrigations.

Feedlot manure was applied in the field at rates of 0, 45, 90, 180, and 360 metric tons/ha to a Holtville clay under irrigated conditions. Holtville clay is a soil with restricted internal drainage. Ceramic cups were installed at various depths in the soil profile to monitor the movement of manganese, nitrate, and soluble organic carbon. The manure greatly increased the amount of soluble organic carbon in the soil solution. An increase in the manure application rate to 180 or 360 metric tons/ha increased the nitrate in the soil solution at 20 and 40 cm, but there were only small differences at 80 and 140 cm. The lack of movement of nitrate to the 80‐cm depth for the high rates of manure application appeared to be due to denitrification, because high nitrate levels were present in the surface soil and sufficient water was applied to leach to this depth. Nitrate leaching was less when manure was applied annually than when it was applied only the first year. Less movement of nitrate to the 80‐cm depth in treatments receiving manure annually seems to be the result of denitrification caused by the higher level of soluble organic carbon. The application of manure did not result in reducing conditions at 20 cm under regular irrigation as measured by redox potential, but the double irrigation schedule caused soil reducing conditions at 20 cm. At 80 cm, manganese in the soil solution was inversely correlated to nitrate level.

Infiltration rates were measured for alfalfa, (Medicago sativaL., cv. WL514) subjected to treatments where wheel traffic was varied in terms of area covered and time of application on a Wasco sandy loam (coarse‐loamy, mixed, nonacid thermic Xeric Torriorthent). Traffic treatments were (i) No‐traffic, (ii) Preplant, (iii) Repeated, and (iv) traffic similar to what a grower would apply. Infiltration rates increased for all treatments, with increases being 240% for treatments without harvest traffic and 140% for treatments with harvest traffic. Increases in infiltration were related to decreases in stand density. Slight packing (traffic) applied before the soil was flood‐irrigated in 1983 increased infiltration rates 20% compared to flooding loosened soil (no traffic). Harvest traffic resulted in slower water movement in the soil.

This study was conducted to determine whether low soil oxygen levels or high soil ethylene reduce tomato (Lycopersicon esculentum) yield in clay soil, when high temperatures are combined with trickle or furrow irrigation. Treatments were daily or weekly trickle irrigations (100 or 120% of pan evaporation) and furrow irrigations (5‐ or 10‐d intervals). Soil oxygen and ethylene levels and soil matric potentials were measured at the 20‐ and 40‐cm depths immediately before and during part of the fruiting cycle. Daily trickle irrigations (100 or 120% of pan evaporation) resulted in oxygen levels of 3 to 6% and matric potentials of 0 to −7 kPa. Furrow irrigation or weekly trickle irrigations resulted in oxygen levels that were about double the values measured for the daily trickle irrigation, and in soil matric potentials of −1 to −60 kPa. Irrigation frequency or rate did not have a significant effect on yield of tomatoes. Soil ethylene levels were low for all treatments (< 1 ppm). Because of higher oxygen level, weekly trickle or furrow irrigation would be preferable to daily trickle irrigation when oxygen may be limiting or when the crop grown is oxygen sensitive.

A field experiment was conducted to evaluate the effect of three water‐table depths (30, 60, and 90 cm) on growth of cotton (Gossypium hirsutumL. var. ‘;Stoneville 213’). Soil aeration, plant water relations, cotton seed yield, and nutrient uptake were measured. The depth of the water table was controlled by adding water to subsurface drains. The optimum water‐table depth was 90 cm or greater with reductions in seed cotton yield of 43 and 25% for water‐table depths of 30 and 60 cm, respectively. As the water‐table depth increased from 30 to 90 cm, concentrations in stems and leaves of N, Ca, K, and Cu increased whereas concentrations of P, Mg, Na, B, and Cl decreased. Increasing the water‐table depth increased the total uptake of all elements studied. When the water‐table depth was increased from 30 to 90 cm, the soil aeration status increased considerably as measured by soil oxygen content, redox potential, and oxygen diffusion rate.

The redox potential (Eh) of irrigated desert soils was evaluated under a wide range of conditions. Factors important in controlling Eh were temperature, flooding time, soil water content, and energy source. Field heterogeneity necessitated using 10 to 20 electrodes (placed in a 30‐cm square) to characterize a treatment. The Eh varied over a short distance with variations not due to poisoning or erratic electrode readings. A 5C increase in temperature at the 15‐cm depth resulted in a 50‐mV decrease in redox potential. The length of soil saturation time correlated directly with the decrease in Eh. When the soil was not saturated during irrigation (sprinkler or drip), Eh decreased less than when the soil was flooded. The amount of energy available to microorganisms has a major effect on how low the Eh decreased in a flooded soil.

Water management is critical for maximum production of alfalfa (Medicago sativaL.) with under irrigation resulting in loss of production and over irrigation resulting in a loss of stand. The purpose of this study was to determine the optimum irrigation rates under high evaporative demand. Growth of alfalfa was evaluated on replicated plots (6 × 6 m) established on a fine textured soil (Typic Torrifluvent, clayey over loamy, montmorillonitic, calcareous hyperthermic family) and differentially irrigated from July 1975 to January 1978. The irrigation treatments were applied at 56, 66, 75 (best estimate of Epand 84% of pan evaporation (Ep) and described as dry, semidry, optimum and wet, respectively. Alfalfa yields increased with increase in water applied. Irrigation at 84% Epfor leaching did not enhance yield over the optimum water treatment possibly because of reduced stand from waterlogging. The protein concentration of alfalfa was higher in dry than in wet treatments in March and November. During the summer, plant temperatures in the dry treatment were up to 7 C higher than in the wet treatment.

A field plot study was conducted to determine the effects of added alfalfa, four flooding times, and two temperatures on EH(Oxidation‐reduction potential) and dissolution of iron and manganese from a silty clay soil. With no alfalfa added, flooding caused only a small decrease in EHat either temperature. The addition of alfalfa at the higher temperature resulted in a reduction in EHto −100 millivolts. Flooding time had no significant effect on EHuntil the third day, when the soils subjected to shorter flooding periods began to dry out. Flooding without organic matter increased the Mn2+and Fe2+concentrations in solution to maxima of only 3.7 and 2.1 ppm, respectively; while the combination of flooding, organic matter and high temperature increased the levels to 46 and 30 ppm. Flooding time had no effect on the dissolution of iron and manganese. The results of this study show the importance of temperature and organic matter on dissolution of iron and manganese and the relation between EHand soluble iron and manganese.

For convenience we shall repeat here the definition by Hawkins, Hill, Reeve and Tyrrell (1, hereafter referred to as HHRT) of a k-map: DefinitionA map is called a k-map if each of the following conditions is satisfied: (i)It is a map on a sphere;(ii)Each face is a connected region whose boundary is a simple closed curve;(iii)Each vertex has at least three edges incident with it and each face has at least three edges on its boundary;(iv)Each face has exactly kedges, and therefore exactly kvertices.

The oxidation and precipitation of Mn was measured in the laboratory under conditions similar to those present in tile lines. The presence of microorganisms capable of oxidizing Mn2+was the most important factor controlling oxidation of Mn. These microorganisms were intimately associated with MnO2collected from tile lines and could not be separated from the MnO2particles. Hence, oxidation of Mn in the presence of microorganisms without the MnO2could not be studied. Surfaces of sand or clay did not catalyze the oxidation. An increase in temperature from 20 to 30C increased the oxidation only slightly. The effects of dissolved oxygen, soluble organic carbon, total salt content, pH, and bicarbonate over the concentration ranges occurring in tile lines were determined using solutions containing manganese oxidizing microorganisms. Soluble organic carbon and total salt content have no significant effect on manganese oxidation. The percent oxygen in the gas mixture did not affect the oxidation rate when it was varied between 1 and 21%. When nitrogen was flushed through the cylinders, the zero oxygen resulted in solution of Mn2+from the manganese dioxide. When the bicarbonate level was raised to 9.0 meq/liter (4% CO2), the oxidation rate was 3 times the rate at the 5.3 meq/liter level of bicarbonate.

A field study of waterlogging and subsequent drying of the soil profile has shown that under irrigation culture in Imperial Valley reducing conditions became prevalent. Reducing conditions, as indicated by declining Ehvalues, became most favorable for dissolution of Mn and Fe near the soil surface. However, the concentrations of Mn2+and Fe2+were lowest near the surface, probably because of their leaching from this zone, and the shorter time of contact between soil solution and soil particles. The concentration of Fe2+and Mn2+were higher in the deeper horizons of the soil profile. In the plow layer, the reducing intensity increased, beginning 9 m away from the tile and reaching a maximum 18‐ to 23‐m from the tile drain. The Ehlevels in the soil profile declined immediately after irrigation began and rose immediately after irrigation stopped indicating the importance of atmospheric oxygen to the oxidation‐reduction status and, therefore, to the solubility of iron and manganese compounds. Soluble organic carbon apparently was not related to the concentration of Mn2+or Fe2+in the soil solution even though the decomposition of soil organic matter is important in oxidation‐reduction reactions in the soil profile.

Various levels of oxidation‐reduction develop in the soil profile during the irrigation and growing season of the cotton (Gossypium hirsutumL.) crop. Reducing intensity increased with depth during the growing season and reached maximum intensity at the 6.10‐m depth. Reducing conditions favorable to increased solubility of Fe and Mn were observed in the surface horizons of the profile during most of the season. Changes in the solubility of manganese and iron occurred with changes in the oxidation‐reduction status in the soil profile. Manganese began to dissolve at 400 mV and became significant at less than 300 mV. Increased concentration of nitrate retarded reduction of oxidized Fe and Mn compounds. The salinity of the soil solution affected the concentration of soluble manganese and iron. The presence of NO3‐‐N in the soil solution in amounts >0.2 ppm retarded the dissolution of Mn compounds. The solubility of manganese and iron can probably be controlled by controlling or regulating the oxidation‐reduction status of the soil profile by reducing the waterlogging period after irrigation to a minimum.

The relation of dissolved oxygen, soluble carbon, and redox potential to the movement of nitrate in soil columns and into submerged tile lines was studied. Columns 300 cm long were drained at depths of 180, 240, or 300 cm with the water table in all columns maintained at 175 cm. After adding ammonium nitrate and irrigating, the peak in nitrate concentration moved downward to the 160‐cm depth, but nitrate concentrations decreased at 180 cm and almost disappeared at the 240‐ and 300‐cm depths. The soil solution at 180 cm contained an average of 5.2 ppm nitrate‐nitrogen and a maximum of 16 ppm. In contrast the soil solution at 240 or 300 cm, which had passed through a submerged zone of 65 or 125 cm, averaged 0.5 ppm and had a maximum concentration of 1.1 ppm. Disappearance of nitrate was associated with decreases in redox potential, oxygen content of the soil solution and oxygen levels in the soil atmosphere, and with increases in soluble iron and manganese. Denitrification occurred without submergence if the soil redox potential was sufficiently low. Results of this experiment indicate that nitrate concentrations probably can be reduced in tile effluents by submerging the tile lines.

The decrease in soil nitrate nitrogen as related to redox potential was studied in the laboratory and in the field in Imperial Valley, Calif. Partial anaerobic conditions were induced in laboratory flasks containing an atmosphere of 21% oxygen by adjusting the soil‐water ratio. When the water content of a soil having a water saturation percentage of 48% was increased to 44.5% or above, large losses of N2gas occurred both with and without addition of organic matter. Significant denitrification coincided with a decrease in the redox potential (Eh). Measurement of redox potential and nitrate concentrations of ground water sampled at various depths in an irrigated field indicated that nitrate concentration was high near the surface but decreased at depths approaching the water table. The diminishing nitrate concentration and redox potential, with depth, indicate that some nitrates were reduced to nitrogen gas before they reached the water table. Only 1.5% of the 280 kg N/hectare applied to a cotton crop (Gossypium hirsutumL.) was discharged in the tile effluent during the growing season. Denitrification in the soil profile apparently reduced the amount of nitrate reaching the tile drainage system.

The loss of gaseous nitrogen compounds when nitrite accumulates in a calcareous silty clay loam during nitrification was investigated under aerobic conditions. Soil to which either (NH4)2SO4, NaNO2, or (NH4)2SO4+ barley straw was added, was incubated at 28C and 31% moisture for 28 days. Samples were maintained under aerobic conditions in a N‐free atmosphere of 21% oxygen and 79% helium. Gas samples were taken every 7 days from the incubation flasks and analyzed, using a gas chromatograph, for gaseous N products evolved. The accumulation of nitrite was measured on separate soil samples incubated in the same manner as the flasks used to secure gas samples. The gaseous N forms produced were N2O and N2. It was found that losses were low even when large amounts (250 ppm) of nitrite‐N accumulated. The gaseous N loss was 1.3% for (NH4)2SO4and NaNO2and 3.6% for the (NH4)2SO4+ barley straw treatment.