No abstract

Forage quality of alfalfa (Medicago sativa L.) often is higher in water‐deficit‐stressed plants than in nonstressed plants. At least part of the improvement could result from a delay in plant development due to the water stress. The objective of this study was to determine forage quality response of alfalfa to water stress and to relate this to corresponding changes in plant maturity, phonological development, and growth. ‘Apollo II’ alfalfa was grown in 100‐L containers set into the ground and protected by a movable rain shelter. Plants were watered either weekly or twice weekly to 112,100, 88, 76, and 64% of field capacity during 2 yr. Regrowth herbage was harvested at five weekly intervals beginning 3 wk after the initial cut. Plants were divided into stem bases (portion of stems below and including the sixth node), stem tops, and leaves before forage quality analyses were conducted. Plant maturity decreased linearly with increasing water stress. Averaged over the harvests, leaf‐to‐stem ratio (LSR) increased from 0.60 in the well‐watered treatments to 0.72 in the most severely stressed treatment. Delayed plant maturity and node number did not account fully for the increase in LSR under water stress. In vitro digestible dry matter (IVDDM) in stems, which increased by about 9% under water stress, was largely accounted for by delayed plant maturity. In stem bases, crude protein (CP) concentration increased by 11% with increasing water stress, even after accounting for differences in plant maturity. Cellulose concentration, expressed on a cell‐wall (CW) basis, decreased whereas CW hemicellulose concentration increased with water stress in both leaves and stems, and these changes were not entirely attributable to differences in plant maturity and growth. Thus, the slowing of plant maturation and growth during water stress accounted for much, but not all, of the changes in forage quality.

To help make decisions on shifting of crop species in water management strategies, information is needed on comparative water use characteristics of the principal row crops. The objective of this study was to compare the water use characteristics of six row crops grown in a replicated and randomized field experiment. Crops were corn (Zea mays L.), grain sorghum (Sorghum bicolor (L.) Moench), pearl millet (Pennisetum americanum (L.) Leeke), pinto bean (Phaseolus vulgaris L.), soybean (Glycine max (L.) Merr.), and sunflower (Helianthus annuus L.). Crops were grown near Manhattan, KS, on Muir silt loam (Cumulic Haplustoll) in 1981 and on Eudora silt loam (JFiuventic Hapludoll) in 1982, and near Tribune, KS, on Ulysses silt loam (Aridic Haplustoll) in both 1981 and 1982.Soil water content was determined to the 3.1-m soil profile depth by the neutron attenuation method. Measured evapotranspiration (ET) was calculated as the sum of soil water depletion, rainfall, and irrigation. Reference ET was calculated by using the original Jensen-Haise equation. The maximum value of measured ET /reference ET was greater for sunflower (1.35) than for the other five crops (ranged from 1.05 to 1.15). The mean daily water use rate of sunflower (6.1 mm d-1 ) was 22% greater than the mean of the other five crops (5.0 mm d-1 ). The mean dry matter water use efficiency was 17.5 Mg ba-• m-• for the group of C 3 crops (pinto bean, soybean, and sunflower) and 33.3 Mg ba-• m-• for the group of C 4 crops (corn, grain sorghum, and pearl millet). Sunflower depleted significantly more water from deeper soil depths (0.99-1.60 m) than the other five crops at Manhattan in 1981 and 1982. Our findings consistently showed that sunflower bad a greater daily water use rate than the other five crops.

No abstract

Research results are lacking that compare the yield benefit from a limited amount of irrigation water applied off-season vs. in-season. Also lacking is a partitioning of field water losses during winter into the profile drainage and evaporation components. The objectives of this work were: (i) to examine grain yield and water use of corn (Zea mays L.) and winter what (Triticum aestivum L.) in irrigation schemes that use fall vs. spring irrigations; and (ii) to partition field water loss during winter into the profile drainage and evaporation components. The field work was done near Tribune, KS, on a Ulysses silt loam soil (fine-silty, mixed, mesic Aridic Haplustoll). Timing of the off-season irrigation (fall vs. spring) did not influence corn grain yield. In irrigation schemes identical except that off-season irrigation was or was not applied, off-season irrigation did not influence corn grain yield significantly. Maximum grain yield benefit in corn from irrigation was achieved when water was applied in-season. In winter wheat receiving only one irrigation, fall irrigated wheat yielded 20SS kg ha-• more grain (3-yr mean) than wheat irrigated only in spring. Among the irrigation schemes containing fall irrigation, there was no significant difference in winter wheat grain yield, even though the total irrigation amount ranged from 1S2 to 4S6 mm. Drainage losses during winter were less than S% as much as evaporation losses at mean profile water contents during winter of less than SO% available soil water. At greater than SO% available soil water, the relative contribution of drainage in profile water loss increased with increasing profile water content. Drainage losses equalled evaporation losses at a mean profile water content during winter of O.S7 m (80% available soil water). Off-season irrigation of corn was not a water efficient practice. Fall irrigation of winter wheat was a water efficient practice that allowed continuous cropping in a region where some rotation that includes fallow is the dryland altern!_ltive.