Methyl bromide (MeBr; CH 3 Br) use for soil fumigation will be banned in 2005 due to its ozone depleting properties. Potential alternative chemicals to replace MeBr include chloropicrin (CP; CCl 3 NO 2 ), 1,3‐dichloropropene (1,3‐D; C 3 H 4 Cl 2 ), iodomethane (IM; CH 3 I), and propargyl bromide (PrBr; C 3 H 3 Br). The goal of this research was to assess changes in soil fungal populations, microbial biomass C (MB C ) and respiration, nitrification potential, and enzyme activities after fumigation with MeBr and alternative fumigants. Four formulations of alternative fumigants (CP, InLine [61% 1,3‐D plus 33% CP], Midas [50% IM plus 50% CP], and PrBr) were applied at commercial rates through drip irrigation systems to two field plots located in main strawberry production areas in California, USA. Soil samples (0–15 cm) were taken at 1, 4, and 30 or 37 wk after fumigant application. Fumigation with MeBr plus CP and the alternative chemicals eliminated soil‐borne fungal pathogens in soil and reduced culturable fungal populations up to 4 wk post fumigation. Soil microbial respiration decreased with fumigant application and was the least (>40% reduction relative to the control) in the PrBr treatment 1 wk after fumigation, while soil MB C was not affected by fumigation. The activities of acid phosphatase and arylsulfatase were generally lower in fumigated soils over the 30‐ or 37‐wk study, and those of β‐glucosidase and dehydrogenase were lower up to 4 wk past fumigation. Potential nitrification rates were substantially reduced (>55% reduction relative to the control) by the fumigants, but rates recovered toward the end of this study. Results of this study suggested that fungal populations and the activities of acid phosphatase and arylsulfatase were more sensitive to fumigation with the tested MeBr and the alternative fumigants than total microbial biomass, microbial respiration, nitrification, and the activities of dehydrogenases and β‐glucosidase. Short‐term impacts of MeBr and its alternative fumigants on microbial activities and enzymatic processes suggest that all the tested fumigants have the potential to alter important microbial and enzymatic functions such as nutrient cycling.
Extensive conveyance loss measurements in watercourses in the Pakistan
Indus Basin indicated water loss in the range of 30 to 50 per cent of the
inflow. This high loss motivated the development and testing of several
system improvements which could be grouped in the categories of improved
maintenance, redesign and earthen reconstruction, and channel lining.
Evaluation of the costs and water savings of these techniques allowed the
formulation of an optimal watercourse improvement strategy. This improvement
strategy, which increases water deliveries to the field by 30 per cent,
is presently being applied on a large scale by the Pakistan On-Farm Water
Management Project. Total farmer provision of labor is evidence of their
support for the program and recognition of its benefits.
Deficit irrigation is often proposed as a method to stretch limited irrigation water supply and increase water productivity. A field study of field crops in the high plains shows that water productivity, in terms of irrigation water applied, generally increases with deficit irrigation. However, in terms of water consumed (ET) water productivity decreases with deficit irrigation greater than about 20%. This results from an initial consumption of about 250 mm to produce initial yield, and the ability of crops to efficiently increase yield with incremental ET increases up to near the potential yield. This result implies, for irrigated basins with limited water where return flows are effectively re-used, deficit irrigation may not produce the highest basin-wide economic return.
Minimizing fumigant emissions is required for meeting air-quality standards. Application of organic materials to surface soil has been effective in reducing fumigant emissions during laboratory tests, but the potential to reduce emissions in the field has not been adequately evaluated. The objective of this study was to determine the effect of incorporated composted manure with or without water applications on fumigant emissions and the potential impact on pest control efficacy under field conditions. Treatments included a bare-soil control, composted dairy manure at 12.4 and 24.7 Mg ha−1, postfumigation intermittent water seals (11 mm water irrigated immediately following fumigation and 4 mm at 12, 24, and 48 h), and incorporation of manure at 12.4 Mg ha−1 combined with the water seals or a high-density polyethylene (HDPE) tarp. Telone C35 was shank-applied at 553 kg ha−1, and emissions of 1,3-dichloropropene (1,3-D) and chloropicrin (CP) were monitored for 10 days. The results indicate that there was no significant difference in emission peak flux and cumulative emission loss between the control and the 12.4 Mg ha−1 manure treatment. The higher manure rate (24.7 Mg ha−1) resulted in lower emission flux and cumulative emission loss than 12.4 Mg ha−1, although the differences were only significant for CP. In contrast, the water treatments with or without manure incorporation significantly reduced peak emission rates (80% reduction) and cumulative emission loss (∼50% reduction). The manure + HDPE treatment resulted in the lowest CP emissions but slightly higher 1,3-D emissions than the water treatments. Reductions in peak emission from water treatments can be important in reducing the potential acute exposure risks to workers and bystanders. This research demonstrated that incorporation of composted manure alone did not reduce fumigant emissions and effective emission reduction with manure amendment may require higher application rates and/or more effective materials than those used in this study.
Low infiltration rates sometimes constrain effective and economical irrigation onsandy loam soils on the east side of Californias San Joaquin Valley. Polyacrylamide(PAM) has increased soil infiltration in other areas of the U.S., especially where soilerosion is a problem. We applied low concentrations of a high molecular weight,moderately anionic polyacrylamide, the type that is being successfully used for furrowerosion control, on Hanford sandy loam soil, in furrow irrigation water. Two years of fieldscale studies and two years of recirculating infiltrometer tests did not show any increasedinfiltration with PAM. There was a slight trend for the PAM to reduce infiltration rates.Laboratory permeameter tests showed decreasing hydraulic conductivity with increasingconcentrations of PAM, likely due to an inapparentlo viscosity of the solution. We concludethat PAM does not reduce aggregate breakdown and surface seal formation sufficientlyfor this soil under these conditions to result in increased infiltration.
Soil erosion occurs when fluid in motion detaches and transports soil particles. Sedimentation occurs when the fluid transport capacity decreases. Both the hydraulic forces of moving water and soil strength and particle size are factors. Under furrow irrigation, the shear of the channel flow against the soil provides the detachment force and is a primary factor in channel transport capacity. With sprinkler irrigation, water drop energy detaches particles, some of which are transported by shallow interrill flow to rills and gulleys.
Erosion occurs when the shear force exerted by
water on a soil unit exceeds the forces binding
that unit to underlying soil. The primary factor
affecting shear force exerted by water on the soil
is velocity of the water. Velocity is determined
by amount of water flowing per unit time and by
slope of the furrow. Relative effects of slope
and furrow flow rate on average water velocity can
be deduced from equation 1, which is Manning's
equation for flow in open channels, where Q is
flow rate (M³/s), A is cross sectional area of
flow (M²), S is slope (M/M), P is wetted perimeter
(M), and n is the coefficient of roughness.
Q = A?/³ S¹/² / (n P²/³)
