No abstract

Synopsis Yield depressions of 10 to 35% in irrigated spring wheat resulted from severe soil moisture stress. Reductions were greatest when stress was imposed during or after heading. Grain yield responses to nitrogen were due largely to increased head population. There appears to be no benefit in the irrigation of spring wheat prior to the boot stage unless moisture stress as indicated by wilting or curling of leaves is observed.

SYNOPSISYield reductions of about 20% under visible moisture stress were measured in Washington state. Causes were as follows: reduction in number of pods before blooming; reduction in number of pods and number of beans per pod during blooming; and reduction in bean weight during ma(uring process. Plant development was retarded by stress before blooming and hastened during blooming and maturing. Irrigation before visible moisture stress appeared to offer no advantage.

Late spring tillage gave the most effective weed control in a winter wheat (Triticum aestivum L.)‐fallow rotation. Downy brome (Bromus tectorum L.) populations in winter wheat on May 1 following plow, one‐way, and sweep plow fallow treatments were 11, 22, and 24 plants per square meter, respectively. Tillages only in July or August with the sweep plow or one‐way did not effectively control downy brome in the subsequent wheat crop. Yields of winter wheat were highest on the mold‐board plow plots followed by one‐way and sweep plow plots tilled in July and again in April. July tillages with the sweep plow or one‐way resulted in the lowest winter wheat yields. During the fallow year, weed control in June was best on moldboard‐plowed plots followed by May tillages with the sweep plow and the one‐way. Quantities of plant residues on the soil surface prior to seeding winter wheat on sweep plow, one‐way, and plot treatments were 896, 728, and 54 kg/ha, respectively.

Synopsis Total and U.S. No. 1 grade yield of Russet Burbank variety potatoes was reduced up to 30% and 58%, respectively, by soil‐moisture stress. Spindled tubers resulted from stress at any time following tuber initiation. Location and intensity of the growth constriction corresponded to the time and intensity of the imposed stress. Late‐season stress hastened maturity and reduced growth cracking whereas mid‐season stress increased growth cracking. Knobby second‐growth was essentially independent of moisture in these experiments. Reduced stem populations resulted in a lower yield and number of tubers and a higher percentage of tubers with knobby second‐growth and growth cracks.