Effects of soil type on soybean crop water use in weighing lysimeters

Abstract

Accurate estimation of crop evaporation from a range of soil types is fundamental to the continued improvement of irrigation management. In this experiment soybean crop evaporation was measured using two weighing lysimeters, one with an undisturbed block of Hanwood loam (L1), the other with undisturbed Mundiwa clay loam (L2). Although both soils have clay profiles the Hanwood loam was much more freely draining. A fresh water-table (EC =0.01 S m-1) was maintained 1 m below the soil surface of each lysimeter after 18 days from sowing (DFS). The crop (vat. Chaffey) was sown on 18 November 1985 both in and around the lysimeters and was harvested 136 days later. Early crop growth was slower in L2 but growth stages after 60 DFS were similar to L1. Estimated leaf area indices exceeded 3 about 51 and 56 DFS for L1 and L2 respectively and were both greater than 9 at 90 DFS. The crop was well watered until at least 110 DFS. However daily rates of evaporation (E) from LI noticeably exceeded those of L2 beginning around 50 DFS and increased to 30% greater for the period 70 to 1 | 5 DFS. This difference was not due to incorrect calibration. Plant water status measurements were generally similar although covered leaf water potential and foliage temperature values indicated that plants on L1 were less well hydrated than on L2. The causes of the E difference are not known, but it was observed that plants in L2 were about 0.1 m shorter than the surrounding plants which were similar in stature to those in L1. It was speculated that this difference in height created a shelter effect which reduced the net radiant energy absorbed by the canopy at low sun angles and reduced the wind speed controlling the turbulent exchange of water vapour. This study highlights the lack of understanding that exists about the effect that small discon-* Visiting Scientist: present address: Texas Agricultural Experiment Station,

Soil type effects on soybean crop water use in weighing lysimeters

“…This effect was consistent with that observed previously (Meyer et al 1990). This occurred despite every attempt to keep both soils in a well watered and well fertilized state and resulted in plants on L2 (Mundiwa clay loam) being about 0.1 m shorter than those plants immediately surrounding.…”

“…Counts of mature trifoliate leaves taken 46 DFS indicated 8.8 leaves per plant for L1 and 7.9 leaves per plant for L2. The slower growth of plants in L2 and the subsequent lower LAI relative to plants in L1 repeated the observations of 1985/1986 (Meyer et al 1990). Plants in L2 were shorter than in L1 (Fig.…”

“…However, in a previous experiment (Meyer et al 1990) we found evaporation rates from soybeans in weighing lysimeters 50 m apart with different undisturbed soil blocks to be up to 30% different at all times during an irrigation cycle, despite good canopy development. This occurred despite good canopy development and maintenance of well watered conditions.…”

“…The experiment was conducted in the same field and lysimeter as described in Meyer et al (1990). The two lysimeters were equipped with undisturbed soil blocks.…”

Reducing the meat and livestock industry's environmental footprint

“…The amount of daily drinking water required by beef cattle is listed in the range of 5–10% of body weight per day, that is, 20–40 L per day for a 400‐kg steer, 13 while that for a 50‐kg sheep is 1.5–3 L per day. The current debate about the amount of water required for livestock production cites values such as 50 000 L 14 or 100 000 L 15 per kilogram of beef, or 170 000 L per kg clean wool 16 . The calculations of Meyer (1998) are based on the annual evapotranspiration rate from pasture measured as 15 ML (or 15 000 000 L) per hectare, 16 and then assessed against a nominal but reasonable annual weight of dressed steak (300 kg) or yield of clean wool (88 kg) per hectare.…”