Philip Eberbach

Crop row spacing and its influence on the partitioning of evapotranspiration by winter-grown wheat in Northern Syria

A study was conducted during the 1996–97 crop growth season at ICARDA in northern Syria, to investigate the influence of wheat canopy architecture on the partitioning of moisture between soil evaporation and crop transpiration, on a soil with high hydraulic conductivity. The study was conducted on the long-term two course wheat-lentil rotation trial, established on a swelling clay soil (Calcixerollic xerochrept). The wheat canopy architecture was manipulated by sowing the crop at either of two row-spacings, 0.17 or 0.30 m, both at a constant sowing rate equivalent to 120 kg ha−1. In this study, evapotranspiration from the crop was inferred from changes in soil moisture content over time, evaporation and rainfall interception were measured daily using microlysimetry, drainage was estimated as being the difference between potential daily evapotranspiration, and the evapotranspiration estimated from the soil water deficit. Between sowing and day 80 (tillering stage), evapotranspiration was calculated to consist mainly of soil evaporation. However, after day 80, transpiration became an increasingly dominant component of evapotranspiration. For both row-spacings, cumulative evapotranspiration over the season was approximately 373 mm. In the narrow-row crop, transpiration and soil evaporation were approximately 185 mm and 183 mm of water respectively. Conversely for the wide row-spaced crop, 172 mm of water was transpired while about 205 mm of water evaporated from the soil surface. While green leaf area index did not differ between row-spacings, the architecture of the crops as a result of sowing affected solar radiation penetration such that more incident radiation was intercepted at the soil surface of the wide row-spaced crop. This is likely to have made some contribution to the elevated levels of evaporation from the soil beneath the canopy of the wide-sown crop.

Applying non-steady-state compartmental analysis to investigate the simultaneous degradation of soluble and sorbed glyphosate (N-(phosphonomethyl)glycine) in four soils

The decomposition behaviour of glyphosate in four Victorian soils was investigated at two temperatures using non-steady-state compartmental analysis. At 25°C, glyphosate degradation was shown numerically to be derived from two different sources where the rate of release from each source behaved in accordance with first-order kinetics. Over the first 40 day period for each of the soils, glyphosate was derived simultaneously from the labile and non-labile phase, whilst after the first 40 days, glyphosate was derived solely from the non-labile phase. At this temperature, the amount of glyphosate partitioned into the labile phase ranged from 24·1 to 34·5%, whilst the amount partitioned into the sorbed, non-labile phase ranged from 67·2 to 74·9%. The half-lives for glyphosate within each phase was calculated and ranged from six to nine days for the labile phase to 222–835 days for the non-labile phase. Glyphosate appeared to be more strongly held in the acidic Rutherglen soil than in the alkaline soils studied, and this was thought to be related to the substantially lower pH and higher Fe content of the acidic soil. At 10°C, glyphosate was shown numerically to be derived from two different sources for two of the soils. However, for the two remaining soils, glyphosate appeared to be derived either from a single phase or from two phases at either the same rate or at differential rates where the rate of release from one phase was sufficiently fast to mask the rate of release from the other. At this temperature, more glyphosate was partitioned into the non-labile phase of the Walpeup and Rutherglen soils than at 25°C. However, the rate of release of glyphosate from this phase increased for the Walpeup soil relative to that at 25°C, but decreased substantially for the Rutherglen soil. This suggests that different mechanisms for the binding of glyphosate into the non-labile phase may exist between soils.

The eco-hydrology of partly cleared, native ecosystems in southern Australia: a review

Water use by the native vegetation that existed in southern Australia prior to European settlement was largely in balance with rainfall. European settlers altered the landscape by clearing land to grow agricultural crops and pastures, and with the introduction of livestock to graze the partly cleared, native ecosystems. The aim of this review is to contrast the hydrology of grazed, partly cleared ecosystems, intact indigenous ecosystems, and entirely cleared agricultural systems in the intensive land-use zone (350–1000 mm annual rainfall zone) of southern Australia. Since European settlement, the areas of forests and woodlands in the Murray–Darling Basin have declined by approximately 64% to make way for agricultural enterprises. Modern-day vegetation surveys estimate between 52 and 58% of the intensive land-use zone of the Murray–Darling Basin has been entirely cleared, while about 40% is in the partly cleared state (disturbed ecosystems with canopy cover exceeding 5%). The replacement of native vegetation by agricultural crops and pastures has disturbed the water cycle that existed prior to European settlement, and has markedly elevated the amount of water leaking beyond the root zone of introduced species, and contributing to groundwater systems. Estimates of annual leakage beneath the root zone of annual crops range from 0 to 63 mm per annum; however, no estimates of leakage for partly cleared woodlands exist. Yet, because the groundwater beneath partly cleared woodlands rises considerably more slowly than under entirely cleared landscapes, it is likely that less water leaks beneath the roots of grazed woody ecosystem. However, aging of these systems by livestock grazing will reduce the numbers of woody individuals and will impact on groundwater recharge.

Response of subterranean clover, balansa clover and gland clover to lime when grown in mixtures on an acid soil

This study compared the relative tolerances of subterranean clover (Trifolium subterraneum L.), balansa clover (T. michelianum Savi.), and gland clover (T. glanduliferum Boiss.) to acid soil conditions. Seed yield, seedling density, herbage production, N2 fixation, and herbage mineral composition of the 3 legumes were assessed when grown on an acid soil (pHCa of 4.3 and 15% exchangeable Al [0–0.10 m]) with and without the addition of lime (CaCO3). Annual legume species were sown in a mixed sward together with burr medic (Medicago polymorpha L.), and in mixtures with either lucerne (Medicago sativa L.), chicory (Cichorium intybus L.), or phalaris (Phalaris aquatica L.). Due to drier than average seasonal conditions, none of the perennial species persisted beyond the first summer. Lime increased the herbage production of annual legumes by 18–22% and total pasture production by 14% in both 2002 and 2003. Subterranean clover was the most tolerant of the annual legumes to acid soil conditions, showing no visible toxicity symptoms and no response to lime in terms of seed yield. In contrast, both balansa and gland clovers exhibited visual symptoms of manganese toxicity in the absence of lime, with Mn concentrations in the shoots of 817 mg/kg and 626 mg/kg, respectively. Both species responded positively to lime with seed yields increasing by 45% and 124%, respectively. Lime increased the proportion of herbage N derived from N2 fixation by subterranean clover from 29 to 40% and by gland clover from 30 to 43%. Lime had no effect on the proportion of N2 fixed by balansa clover (29–31%), suggesting a suboptimal symbiosis of rhizobia with that species. Adding chicory or phalaris to the pasture mix increased sward herbage production in the establishment year by 39% and 21%, respectively. Based on leaf symptoms and herbage yield responses to lime, Mn toxicity was present in lucerne with tissue levels of up to 916 mg/kg, but no symptoms were observed in chicory (1129 mg/kg) or phalaris (403 mg/kg). Chicory and phalaris were more tolerant of acidity and high levels of Mn than lucerne, gland clover, and balansa clover. The study highlighted the value of the small-seeded annual legumes, balansa clover and gland clover, to the production of mixed pasture swards even in drier than average seasonal conditions. Although more sensitive to acid soils than subterranean clover, they set a greater number of seeds and, in the case of balansa clover, a greater weight of seed under moisture stress in the establishment year than the larger seeded subterranean clover.

Effect of herbicide residues in a sandy loam on the growth, nodulation and nitrogenase activity (C2H2/C2H4) of Trifolium subterraneum

The herbicides 2,4-D, amitrole, atrazine, diclofop-methyl, diquat, paraquat and trifiluralin were applied at rates of 0, 2, 5 and 10 μg ai. g−1 to a sandy loam soil and allowed to degrade for 120 days. After this period, subterranean clover seedlings were transplanted into treated soil and the effect of herbicide residues on plant growth, number of nodules formed and nitrogenase activity was investigated. At all rates of atrazine and chlorsulfuron, and at all rates of amitrole in excess of 2 mg ai g−1 of soil, sufficient herbicide remained to be lethal to the seedlings. When amitrole was applied at the rate of 2 mg ai g−1 of soil, plant growth, nodulation and nitrogenase activity of plants were reduced. Residues of diquat reduced all plant parameters studied while, residues of 2,4-D reduced plant growth and nodule formation, but plant nitrogenase activity was unaffected. Residues of trifluralin had no effect on plant growth parameters but the number of nodules formed per plant was reduced. Residues of paraquat and diclofop-methyl had no effect on any of the plant parameters studied.

Evaluation of the effects of mulch on optimum sowing date and irrigation management of zero till wheat in central Punjab, India using APSIM

Highlights • Late October to early November sowings gave maximum yield and irrigation WP of both mulched and non-mulched wheat in NW India.• Mulch increased yield of late October-early November sowings, but decreased yield of later sowings.• Mulch reduced the number of irrigations by one in about 50% of years under practical irrigation schedules (∼50% SWD).• Maximum yield on sandy loam was at 10% SWD and at 10–50% SWD on clay loam, and least irrigation and highest WPI was at 70% SWD scheduling on both soils.• Maximum WPET occurred with scheduling at 40–60% and 70% SWD on the sandy loam and clay loam, respectively.

Sorption and degradation of fipronil in flooded anaerobic rice soils.

The fate of fipronil in flooded, reductive rice soils was modeled using a conceptual model. Rate constants for the various sorption and degradation processes were calculated from experimental studies involving intact soil cores, and the reductive degradation constant was used to calculate half-lives for fipronil on each soil. The data predicted that fipronil was subject to rapid, reductive degradation or immediate sorption to the soil and any sorbed fipronil desorbed was reductively degraded. The reductive metabolite, fipronil sulfide, accumulated over the 184 day duration of the experiment and sorbed rapidly to the soil, where it accumulated and did not appear to degrade. Neither fipronil nor fipronil sulfide was found beyond the top 1 cm of soil in Yanco soil, while a small amount of each chemical was found up to 4 cm deep in the Coleambally soil profile.

The sorption and degradation of the rice pesticides fipronil and thiobencarb on two Australian rice soils

The sorption and degradation of the rice pesticides fipronil and thiobencarb on 2 Australian rice-growing soils were investigated. Greater sorption of both pesticides occurred on the soil containing less organic carbon, possibly as a result of the type of organic carbon present, rather than the absolute amount. While sorption tended to appear greater in the 0–10 mm layer than the 10–20 mm layer, analysis showed the difference was not significant (P > 0.05). Under aerobic conditions, a lag period of 20 days in the degradation of thiobencarb occurred on the Yanco soil, but rapid degradation occurred on the Coleambally soil, and, while unlikely, may have been a consequence of preconditioning of the Coleambally soil microbial population. Degradation of thiobencarb under both non-flooded anaerobic and flooded anaerobic conditions differed significantly (P < 0.05) compared to aerobic conditions. Conversely, fipronil degraded rapidly over the first few days and then slowed, and was attributed to the co-metabolism of fipronil by soil microbes. While fipronil sulfide was produced under all oxic/anoxic conditions, its concentration was greatest under flooded anaerobic conditions, possibly as a result of greater exclusion of oxygen from the soil by the floodwater.

Pore Mn2+ dynamics of the rhizosphere of flooded and non-flooded rice during a long wet and drying phase in two rice growing soils

Flooded rice soils produce elevated concentrations of soluble manganous manganese (Mn(2+)) that could be potentially toxic to subsequent crops. To provide insight into how soil pore Mn(2+) changes its concentration in a rice and post rice drying soil, we used an artificial microcosm system to follow Mn(2+) concentrations in two different soil types (red sodosol and grey vertosol) and under two irrigation regimes (flooded and saturated). Soil pore water was collected from four different depths of soil (2.5 cm, 7.5 cm, 15 cm and 25 cm) and Mn(2+) concentrations were analysed during and after the rice phase over a one year cycle. Mn(2+) increased with the advancement of anaerobic conditions at all soil depths, but the concentration was higher in flooded soil compared to saturated soil. Initially, the highest concentration of Mn(2+) was found at a depth of 7.5 cm, while at the later stage of rice growth, more Mn(2+) was found in the deepest sampling depth (25 cm). Plants grown in saturated soils showed a delay in flowering of approximately 3 weeks compared to flooded cultures. Moreover, plants grown in flooded soil produced more tillers and leaf area than those grown in saturated soil. Peak concentrations of soil Mn(2+) were associated with the reproductive stage of rice growth. Mn(2+) concentrations decreased after drainage of water. In post rice soils, Mn(2+) remained elevated for some time (lag phase), and then rapidly declined. Regression analysis revealed that the process of oxidation of Mn(2+) to Mn(4+) following water drainage decreased with soil depth.

Variable impact of rice (Oryza sativa) on soil metal reduction and availability of pore water Fe2+ and Mn2+ throughout the growth period

ABSTRACT Flooding of wetland or agricultural soils can result in substantial alteration of the pore water trace metal profiles and potentially also influence the bioavailability of other trace elements adsorbed to the insoluble oxides. Experimental microcosms were used to quantify the impact of rice (Oryza sativa) plants across an entire growing cycle on the concentrations of Mn2+ and Fe2+ in two soil types (red sodosol and grey vertosol). Two water management treatments were included: a standard flooded treatment and a saturated treatment (−3 kPa). Soil pore water profiles were established from samples collected at four sampling depths (2.5, 7.5, 15 and 25 cm) on 50 occasions. Fe2+ and Mn2+ concentrations were higher in flooded soil than in saturated soil and greatest at a depth of 7.5 cm. The presence of rice plants increased Mn2+ concentrations in flooded soils, but tended to decrease Mn2+ concentrations in saturated soils. The influence of rice plants on Fe2+ concentrations was greatest at a depth of 7.5 cm. Changes in soil pore water Fe2+ and Mn2+ concentrations due to the presence of rice plants were correlated with flowering and reproduction.