Abstract
The dynamics of sap flow in relation to plant morphology and weather conditions during reproductive growth of soybean (Glycine max. L. Merr.) influence decisions pertaining to efficient irrigation management and other inputs for high yields. Field studies began in 2017 at Marianna, Arkansas to measure moisture dynamics of soybeans during seed fill (R5 to R7) using heat balance stem flow gauges. Sap flow was highly correlated to solar radiation with maximum rates observed during beginning seed fill (R5). A solar radiation efficiency (SRE) value, calculated as hourly sap flow rate per Watt-hour of solar radiation (g/Wh2), is proposed. The SRE relates to crop water demand and hydraulic resistance of the soil-root-stem-leaf-pod-seed pathway. SRE values ranged from 0 - 1.2 g/Wh2. Soil moisture, growth stage, time of day, and weather conditions influenced the SRE, with higher values observed in the morning, late afternoon, and during R5 growth. Peak sap flows of 39 g/h at R5, 25 g/h at R6, and 3 g/h at R7 occurred. The ratio of measured sap flow to estimated crop evapotranspiration was 0.9 to 1.3 during R5 to R6.9 (maximum dry matter), but dropped to 0.2 at R7. Further research is needed to better understand late season reproductive moisture dynamics in soybeans.
Highlights
Irrigation, rainfall, and evapotranspiration varied with growth stage and generally declined from R5 to R7 growth (Figure 1)
Maximum sap flow occurred in the middle of July
To determine the relationship between soil water and sap flow, we looked at the correlation between sap flow and soil water in 0 - 76 cm depths in time intervals between irrigations and rainfalls from 17-23 July 2017 to 8-14 Aug. 2017 (Figure 4)
Summary
L. Merr.) water dynamics in relation to the soil moisture content and weather conditions during late reproductive growth stages will improve water management and irrigation scheduling and irriga-. Water demand of soybean plants varies with growth stage and weather conditions [1]. In every moment of the plant life cycle, nutrients in soil water are absorbed through the plant root system and transported to stems, leaves, and pods by osmosis hydraulic potentials created by xylem and phloem microcapillaries and leaf evapotranspiration. Soil water resistance and hydraulic conductance plant regulate sap flow. Some authors found that hydraulic conductance of the soybean plant was not flow dependent [2]. Investigations of sap flow characteristics in different soil water resistance, growth stages and weather conditions can improve irrigation management decisions
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