No abstract

Two lucerne (Medicago sativa) varieties, an anecdotally waterlogging-intolerant old New Zealand variety, Grasslands Wairau, and a reputedly waterlogging-tolerant new variety, Pioneer 54Q53, were subjected to waterlogging stress and a range of physiological and agronomic measurements performed. Waterlogging stress was characterized by measurement of soil oxygen depletion and soil carbon dioxide accumulation. Both varieties exhibited strong responses to waterlogging stress, including reduction in leaf soluble protein concentration, photosynthetic rate and tap root weight, but also exhibited differences in response, notably a decrease in carboxylation efficiency and in the steady-state quantum yield of electron flow through PSII (FPSII) in Wairau, but not in Pioneer. Implications for understanding of waterlogging effects on photosynthesis, and for field management of lucerne on wet soils are discussed.

Single‐eared (Hy × C103) and two‐eared (R71 × B60) corn (Zea mays L) hybrids were grown with their roots confined in 8− ✕ −24‐inch plastic‐lined, soil‐filled trenches. They were subjected to equally severe moisture stress at tassel emergence, silking‐pollination and blister kernel stages. The two‐eared variety was more tolerant to moisture stress at the pollination and blister kernel stages than the single‐eared variety. There was no significant difference in the total grain yield of the varieties to the moisture stress at tassel emergence. Silking was delayed in both varieties during moisture stress at pollination; however, this delay in silking did not reduce the fertilization of the ears and the grain yields of the two‐eared variety as much as the single‐eared variety. The two‐eared variety extracted significantly more water (1–2%) from the soil when under moisture stress. A method for measuring the relative turgidity (RT) of the leaves of the corn plants was developed, and the RT of each leaf on the corn plant was different. The RT decreases from apex to base, with each succeeding leaf. Moisture‐stressed corn plants had RT values 18 percent lower in the leaves near the ear shoot than in the leaves near the tassel. This difference in RT could account for the lack of silk emergence while the tassels continued to shed pollen.

The effect of corn (Zea mays L.) leaf orientation on grain yield and production practices has been the subject of conflicting reports over the past few years. Plant population is reported to be the cause of the discrepancies. The objectives of the present study were to determine the effect of plant population and leaf orientation on corn plant efficiencies and their interaction. Two contrasting leaf angles were compared by the use of near‐isogenic versions of the single‐cross hybrid (Hy2 ✕ C103) consisting of the liguleless (lg2) and its normal counterpart. Light penetration, light reflection, total dry matter production, and grain yields were measured to determine the effect of the leaf orientation, leaf area, and plant densities on corn production. Leaf angles of the two versions differed by 20°. Nine percent more light was intercepted by the horizontally oriented leaf type (HL). Plant populations (from 39,305 to 88,958 plants/ha) had no effect on leaf angle. High populations resulted in mutual shading which reduced the yield per plant. The mean leaf area per leaf of the HL was 17% larger than the vertically oriented leaf type (VL). Plants grown at 69,189 plants/ha had smaller leaves than those at the 49,421 population. Defoliation above the ear removed less leaf area than any of the other treatments and produced the smallest grain yield. All defoliation treatments reduced grain yield. Reflectors did not increase yield. Leaf orientation had little effect on corn production in rows spaced 76 cm apart.