An integrated modelling toolbox for water resources assessment and management in highland catchments: Model description

Water and land resource competition and environmental degradation pose difficult questions for resource managers. In particular, the ensuing trade-offs between economic, environmental, and social factors and their spatiotemporal variability must be considered when implementing management policies. This paper describes an integrated modelling toolbox that has been developed for highland catchments – specifically the Mae Chaem catchment in Northern Thailand. This toolbox contains models of crop growth, erosion and rainfall-runoff, as well as household decision and socioeconomic impact models. The approach described advances and complements previous approaches by: considering more complex interactions between land-use decisions and the hydrological cycle; modelling household decisions based on uncertain expectations; and assessing impacts of changes not only on flows and household income, but also on subsistence production and erosion. An example of the types of trade-offs and scenarios that can be assessed using the integrated modelling toolbox is also presented. This demonstrates that for the scenarios presented, the magnitude and direction of impacts simulated by the model is not dependent on climate. Further testing of the model is demonstrated in a companion paper. Overall, the plausibility of the model is shown.     

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

Summary Different soils are known to affect the amount and distribution of both available water and roots. Optimising irrigation water use, especially when shallow water-tables are present requires accurate knowledge of the root zone dynamics. This study was conducted to determine the effect of two soil types on root growth, soil water extraction patterns, and contributions of a water-table to crop evaporation (E). Two weighing lysimeters (L1 and L2) with undisturbed blocks of soil were used. The soil in L1 had higher hydraulic conductivity and lower bulk density than that in L2. Well watered conditions were maintained by irrigation for the first 110 days from sowing (DFS). Root length density (RLD) was calculated from observations made in clear acrylic tubes installed into the sides of the lysimeters. Volumetric soil water contents were measured with a neutron probe. A water-table (EC = 0.01 S m^-1) was established 1 m below the soil surface 18 DFS. RLD values were greater in L1 than L2 at any depth. In L1, maximum RLD values (3 × 10⁴ m m^-3) were measured immediately above the water-table at physiological maturity (133 DFS). In L2, maximum RLD values (1.5 × 10⁴ m m^-3) were measured at 0.42 m on 120 DFS and few roots were present above the water-table. From 71 to 74 DFS, 55 and 64% of E was extracted from above 0.2 m for L1 and L2, respectively. In L2, extraction was essentially limited to the upper 0.4 m, while L1 extraction was to 0.8 m depth. Around 100 DFS the water-table contributed 29% (L1) and 7% (L2) of the water evaporated. This proportion increased rapidly as the upper soil layers dried following the last substantial irrigation 106 DFS. Over the whole season the water-table contributed 24% in L1 and 6.5% in L2 of total E.     

Infiltration parameters from optimisation on furrow irrigation advance data

Knowledge of the soil infiltration parameters is necessary for efficient furrow irrigation. A method is proposed for the determination of the parameters in the Kostiakov-Lewis infiltration equation from measurements of the furrow irrigation advance and inflow. The method employs a volume balance model using optimisation to minimise the error between the predicted and measured advance and differs from existing approaches in that only advance data and inflow rates are required. The average cross sectional area of the furrow and the final infiltration rate are treated as fitted parameters and need not be measured. A simple but effective optimisation algorithm is developed which allows for the solution of the four parameters without user input. The speed and simplicity of the optimisation may lead to application in real-time control of furrow irrigation. Received: 16 August 1995     

Subsurface drip irrigation for corn production: a review of 10 years of research in Kansas

Kansas State University initiated studies in 1989 to develop the methodology for successful application of subsurface drip irrigation (SDI) for corn production on the deep silt loam soils of the Central Great Plains, USA. Irrigation water use for corn can be reduced by 35–55% when using SDI compared with more traditional forms of irrigation in the region. Irrigation frequency has not been a critical issue when SDI is used for corn production on the deep silt loam soils of the region. A dripline spacing of 1.5 m has been found to be most economical for corn grown in 0.76 m spaced rows. Nitrogen fertigation was a very effective management tool with SDI, helping to maximize corn grain yield, while obtaining high efficiencies of nitrogen and water use. The research SDI systems have been utilized since 1989 without replacement or major degradation. SDI systems lasting 10–20 years are cost competitive for corn production with the more traditional forms of irrigation in the Great Plains for certain field sizes.Communicated by P. Thorburn     

Irrigation scheduling of cotton in a climate with uncertain rainfall

Summary An investigation was made of the irrigation requirements of cotton grown in a sub-humid environment with significant but highly variable rainfall. In the first year of the study, no additional yield benefits accrued to subsequent irrigations following a pre-emergent irrigation due to above average rainfall (550 mm) throughout the growing season. In the second year a similar rainfall amount (502 mm) fell but significant yield increases to irrigation resulted due to the uneven distribution of the rainfall. The main effect was associated with later rains which influenced the number of bolls set. The maximum amount of water extracted by cotton from a deep grey cracking clay was 178 mm. It was found that 70% of this amount could be depleted before irrigation without loss of yield. Crop evapotranspiration varied from 607 mm with no irrigation after emergence to 775 mm following three irrigations. Irrigation was associated with significant losses from rainfall runoff. Too frequent irrigation creates a risk that soil will be too wet to permit utilisation of natural rainfall. Therefore, the use of soil water information to maximise the interval between irrigation is proposed as a necessary basis for efficient irrigation management.     

Quinone Binding Sites of Membrane Proteins as Targets for Inhibitors

Quinones are a central component of most photosynthetic and respiratory electron transfer chains. The proteins that reduce and oxidise these quinones have quinone binding sites—Q sites—that are good targets for pesticides. This paper reviews the diversity of these sites, their possible structure, and the types of compounds that act upon them.     

Using the RUSLE to identify factors controlling erosion rates of mine soils

Observable differences in particle size, smoothness and compaction between cap site (slope 2·8 per cent) and batter site (slope 20·7 per cent) surfaces on the waste rock dump at Ranger Uranium Mine were quantified in terms of revised universal soil loss equation (RUSLE) parameter values. Cap site surface material had a K_m (erodibility corrected for sediment density) of 0·030 and batter site surface material had a K_m of 0·0056. Using these K_m values (derived from particle size distributions), slope length and steepness (LS) factors of 0·36 for the cap site and 3·66 for the batter site, and a cover (C) factor of 0·45 for the cap site and 0·16 for the batter site, the RUSLE predicts an erosion rate from the cap site that is 1·9 times greater than erosion from the much steeper batter site. The RUSLE indicates that the finer particle size and blocky soil structure of the cap site (D₅₀ = 0·91 mm) compared with the looser granular structure of the batter site (D₅₀ = 1·74 mm) strongly influence erosion. The predictions are similar to observed soil losses from erosion plots on these sites under rainfall simulation events, for which the measured erosion rate from the cap site was approximately twice that from the batter site. For the RUSLE to predict the observed erosion rates, the support practice (P) factor for the cap site would have to be approximately 30 per cent greater than the P factor for the batter site. The higher cap site P factor probably results from smoothing and compaction caused by vehicle movement across the surface. Compaction is considered to have greatly reduced infiltration capacity, thus increasing the erodibility of the cap site. Vehicles probably also crushed the surface material at the cap site, creating the observed finer particle size distribution and further increasing the erodibility. Compaction, through its effects on erodibility (K_m) and surface roughness (P), is concluded to be the major cause of higher erosion from the cap site, even though the slope steepness is 10 times less. Parameterisation of the RUSLE quantifies the differences between sites and explains the unexpected erosion rates observed. The results highlight the need for careful management of rehabilitated sites to avoid increases in erosion which may arise from compaction by machinery.