High rates of manure were added to field plots of a Holtville silty clay (Typic Torrifluvents) soil in an irrigated desert region, and their effects on the soils' chemical and physical properties were measured for 9 years.Manure applications resulted in large losses of nitrogen (N), increased potassium (K) levels, increased phosphorus (P) availability, increased water intake rates during the growing season, and an N mineralization rate of about 5% after the first year. At high rates of manure application only 42% of the N applied could be accounted for. One application of 180 t/ha of manure in 1971 doubled the NaHCO3‐extractable P levels in the soil in 1979 compared with that of plots that did not receive manure. The application of manure had only a small or no effect on the water intake rate when it was measured between cropping periods on plots that had been recently tilled, but differences were large when water intake rates were measured while the crop was growing. The increased water infiltration rates during the growing season would be important because of increased crop yields in areas affected by salinity.

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.

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.

Greenhouse studies were conducted to determine the potential of nitrate reductase activity (NRA) as an indicator of the change of N concentration of cotton (Gossypium hirsutum L.) shoots. The results showed that cotton petiole in vivo NRA was not significantly different from NRA in leaf blades during vegetative growth. Nitrate reductase activity (in vivo) in cotton petioles was significantly higher than in leaf blades during reproductive growth. When plants were in the three‐mature‐leaf stage, petiole NRA contributed 16% of total cotton shoot NRA. The petiole biomass was 14% of total shoot fresh weight and 8% of total shoot dry weight. Petiole NRA of plants in the vegetative growth stage increased from 39 to 68 pmol NO−2 g1− FW (fresh weight) s−1 when supplemented with nitrate‐N. These results indicate that cotton petiole NRA is significant and its assay has potential for incorporation into monitoring systems that determine the change of N concentration in cotton shoots.

Losses of alfalfa (Medicago sativa L.) 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 O2 fell 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 O2 stress under high temperature extends over many irrigations.

Soil oxygen levels and soil water matric potentials were measured at the 15‐, 30‐, and 60‐cm depths in plots subjected to flooding times of 15, 25, 35, and 45 hours. A decrease to 6% O2 or less in the soil for > 24 hours resulted in substantial losses of alfalfa (Medicago sativa L.). Soil O2 content decreased more at the 15‐cm depth as compared with the 30‐ or 60‐cm depths because of higher matric potential. The critical matric potential that restricted O2 movement was about −11 cbars.