No abstract

A series of N fertilization experiments was conducted over three growing seasons, at three elevations, utilizing two varieties of ‘Acala’ cotton (Gossypium hirsutum) on two soil types. The treatments consisted of various rates and timing of N fertilizer applications. Data indicated that N deficiency at early growth stages limited development of vegetative branches, internode elongation, and fruiting, particularly in “one‐peak” flowering areas. Cotton plants can compensate by increased fruiting in longer seasons or “two‐peak” flowering areas when adequate N is available during late season following earlier N deficiency. The effect of N applications on fruiting and yield was dependent on the intial N fertility of the soil and the yield possibility. When N was limited, yield and fruiting were increased by N applications. Petiole analyses were used to show the relationship between N nutrition and yield and fruiting.

Wheat acreage in Arizona has increased tenfold since the introduction of high yielding semidwarf spring wheats (Triticum aestivum L.). Because of the higher yield potential of these wheat cultivars, many growers have applied more fertilizer without evidence that these semidwarf spring wheats require more nutrients. This study was initiated to evaluate the effect of N and P fertilization on the growth and yield of semidwarf spring wheat and to develop a workable tissue test to determine the nutritional status of the wheat plan. Tissue samples for chemical analysis were taken from uheat plants in three different field experiments. These experiments consisted of 1) six rates of N and three rates of P, 2) six rates of N and six wheat cultivars, and 3) six rates of N and three wheat cultivars. The NO3‐N concentration in the lower 5 to 8 cm of the stem indicated the N status of the wheat plant. Minimum levels of NO3‐N for different stages of growth were established for Southwestern Arizona conditions. In two experiments excessive N decreased yields slightly when compared to sufficient levels of N. The main effects of N on grain yield components were to increase the number of heads/unit area, increase the number of seeds/ head, and decrease the weight of individual seeds. The total N content in the grain increased with increased N applications. Determination of P in the lower portion of wheat stems was not found to be suitable for indicating the P status of the crop.

Phosphorus sorption isotherms were constructed for two Idaho soils with widely different chemical properties. The soils were equilibrated with various amounts of Ca(H 2 PO 4 ) 2 in 0.01 M CaCl 2 for 1, 3, 7, and 11 days at temperatures of 5°C and 20°C. The two soils which had been equilibrated previously for 11 days at 20°C with various amounts of Ca(H 2 PO 4 ) 2 in 0.01 M CaCl 2 were desorbed at 5°C and 20°C.The rates of sorption and desorption were decreased as the equilibration temperatures were lowered. The effect of temperature on these processes was detected during the first day of equilibration. Less P was found in the equilibrating solution at the lower temperature. The two soils varied widely in sorption and desorption properties.