Grant Cardon

Impact of irrigation timing on simulated water-crop production functions

Abstract Estimates of the effects of alternative discrete irrigation water scheduling options on consumptive use or evapotranspiration and on crop yield are developed for a northeastern Colorado case study. The analysis proceeds from the premise that farmers, rather than considering irrigation water as a continuously variable input, tend to treat irrigations as discrete events, and make scheduling decisions as choices among numbers of irrigations of approximately equal volume. The van Genuchten-Hanks model is employed to develop a transient-state water-crop production function model. Results for two crops – corn grain and edible dry beans – are presented here. Findings are that the effect of the number of irrigations on evapotranspiration and yield per hectare varies widely, depending upon the timing of applications. When farmers can choose the optimal timing of irrigations, a reduced number of irrigations has a relatively limited adverse effect on crop production until irrigations are reduced to less than four per season. However, there are many situations in which an inability to apply water can result in a very large reduction from potential maximum yield, particularly if water is withheld early in the season and/or during the rapid growth period of the crops. In many contexts of irrigation water management, water policy analysts will wish to consider the more realistic discrete-input simulation model for policy evaluation.

Soil boron and selenium removal by three plant species

High concentrations of boron (B) and selenium (Se) naturally found in the environment are detrimental to sustainable agriculture in the western USA. Greenhouse pot experiments were conducted to study B and Se uptake in three different plant species; Brassica juncea (L.) Czern (wild brown mustard), Festuca arundinacea Schreb. L. (tall fescue), and Brassica napus (canola) were grown in soil containing naturally occurring concentrations of 3.00 mg extractable B kg−1 and 1.17 mg total Se kg−1 soil. During the growing season, four intermediate harvests were performed on wild mustard and tall fescue. Final harvest I consisted of harvesting wild mustard, canola, and clipping tall fescue. Final harvest II consisted of harvesting wild mustard, which had been planted in soil in which wild mustard was previously grown, and harvesting previously clipped tall fescue. The greatest total amount of above ground biomass and below surface biomass was produced by tall fescue. Plants were separated into shoots and roots, weighted, and plant tissues were analyzed for total B and Se. The highest concentrations of tissue B were recovered in shoots of wild mustard and canola at final harvest I, while roots from tall fescue contained the highest concentrations of B irrespective of the harvest. Tissue Se concentrations were similar in all plants species. Soils were analyzed for residual B and Se. Extractable soil B concentrations at harvest times were lowered no less than 32% and total Se no less than 24% for all three species. The planting of wild mustard, canola, or tall fescue can reduce water-extractable B and total Se in the soil.

Comparison of dry ashing and wet acid digestion on the determination of boron in plant tissue

Abstract Dry ashing and wet acid digestion of selected plant tissues were conducted and evaluated for their effectiveness in the spectrophotometric determination of boron (B) using the Azomethine‐H method. In dry ashing, two parameters were varied: ashing aids and length of oxidation period. In wet acid digestion, two different mineral acids were used and the length of the oxidation period was varied between 12 and 24 h. Results showed that samples treated with sulfuric acid in dry ashing had the lowest recoveries of B. Boron concentrations in tissues oxidized for 12 h in wet acid digestions were at least 40% higher than the results obtained for any dry ashing technique.

Simulated crop production under saline high water table conditions

SummaryMany irrigated lands in semi-arid regions of the world are underlain with saline high water tables. Water management is critical to maintain crop productivity under these conditions. A multi-seasonal, transient state model was used to simulate cotton and alfalfa production under various irrigation management regimes. The variables included in-season water application of 1.0 or 0.6 potential evapotranspiration (PET), and 18 or 33 cm pre-irrigation amounts for cotton. The water table was initially at a 1.5m depth and a 9 dS/m salinity. A impermeable lower boundary at 2.5 m depth was imposed. Irrigation water salinity was 0.4 dS/m. Climatic conditions typical to the San Joaquin Valley of California were used for PET and precipitation values. The simulations were for no-lateral flow and also lateral flow whereby the water table was raised to its initial level prior to each irrigation event. Uniform application of 1.0 PET provided for relative cotton lint yields and alfalfa yields of 95% or more for at least 4 years. In-season irrigation of cotton with 0.6 PET had higher yields when associated with a 33 cm rather than an 18 cm pre-irrigation. Lateral flow provided for higher cotton lint yields production than the no-lateral flow case for each pre-irrigation treatment. The beneficial effects of lateral flow diminished with time because of the additional salt which accumulated and became detrimental to crop production. Substantial alfalfa yield reductions occurred after the first year when irrigation was set at 0.6 PET regardless of other conditions. Evaporation losses from the soil during the cotton fallow season were higher when the soil water content entering the fallow season were higher.

Influence of laboratory methods on calcareous saline soils for EC measurement and leaching

Abstract Electrical conductivity (EC) methods were tested using combinations of surrogate irrigation (SI) waters, soil salinity levels, and soils ground or retaining aggregates. The EC varied in low-salinity soils saturated with SI; the sum of the baseline ECe and SI EC were not equal to the measured EC. The baseline ECe and the SI EC sum in the high‐salinity ground soils were not equal to the any measured ECs. Salt‐removal potential from gypsiferous soils was examined using multiple extractions from the same soil sample. Calcium concentrations remained consistent over 14 extractions, whereas Na concentrations decreased. The ECe decreased from more than 8 dS m−1 in the initial extraction, to approximately 4 dS m−1 by the 9th to 14th extraction. Multiple extraction data suggest that improved leaching will not lower soil ECs to less than approximately 4 dS m−1 because of gypsum and calcite reservoirs in the tested soils.

Use of Steel Slag to Remove Dissolved Phosphorus from Lagoon Supernatant

Manure management and increased soil phosphorus levels are issues faced by many dairy farmers. A method to reduce the phosphorus content of dairy lagoon effluent is needed to allow continued effluent application for nitrogen and irrigation water without exceeding the phosphorus needs of the crop. This study examined the feasibility of using electric arc furnace (EAF) steel slag to remove dissolved reactive phosphorus from dairy lagoon effluent. Treatment columns filled with EAF steel slag had dairy lagoon effluent added with a 12 h retention time batch flow over a course of 106 days. Samples were collected weekly and analyzed for dissolved reactive phosphorus and pH. Differences between the influent and effluent for each treatment column were determined. Four treatments were compared: warm temperatures, cold temperatures, high organic content, and a gravel control. Significant differences were observed among treatments. Cold temperature resulted in the greatest phosphorus removal efficiency, followed by high organic content, warm temperature, and the gravel control. Among the EAF steel slag treatments, the average overall phosphorus removal efficiency for the 106-day study ranged from 63% to 71%.

Use of Steel Slag to Reduce Phosphorus Loading in Animal Waste Handling Systems

Manure management and increased soil phosphorus levels are issues faced by many dairy farmers. A method to reduce the phosphorus content of dairy lagoon effluent is needed to allow continued effluent application for nitrogen and irrigation water without exceeding the phosphorus needs of the crop. This study examined the feasibility of using electric arc furnace (EAF) steel slag to remove phosphorus from dairy lagoon effluent. Treatment columns filled with EAF steel slag had dairy lagoon effluent added with a 12-hour retention time batch flow over a course of 106 days. Samples were collected weekly and analyzed for dissolved reactive phosphorus and pH. Differences between the influent and effluent for each treatment column were determined. Four treatments were compared: warm temperatures, cold temperatures, high organic content, and a gravel control. Significant differences were observed among treatments. Cold temperature resulted in the greatest phosphorus removal efficiency, followed by high organic content, warm temperature, and the gravel control. Among the EAF steel slag treatments, the average overall phosphorus removal efficiency for the 106-day study ranged from 63% -71%.