Earthworm populations and growth rates related to long-term crop residue and tillage management

Conventional tillage creates soil physical conditions that may restrict earthworm movement and accelerate crop residue decomposition, thus reducing the food supply for earthworms. These negative impacts may be alleviated by retaining crop residues in agroecosystems. The objective of this study was to determine the effects of various tillage and crop residue management practices on earthworm populations in the field and earthworm growth under controlled conditions. Population assessments were conducted at two long-term (15+ years) experimental sites in Québec, Canada with three tillage systems: moldboard plow/disk harrow (CT), chisel plow or disk harrow (RT) and no tillage (NT), as well as two levels of crop residue inputs (high and low). Earthworm growth was assessed in intact soil cores from both sites. In the field, earthworm populations and biomass were greater with long-term NT than CT and RT practices, but not affected by crop residue management. Laboratory growth rates of Aporrectodea turgida (Eisen) in intact soil cores were affected by tillage and residue inputs, and were positively correlated with the soil organic C pool, suggesting that tillage and residue management practices that increase the soil organic C pool provide more organic substrates for earthworm growth. The highest earthworm growth rates were in soils from RT plots with high residue input, which differed from the response of earthworm populations to tillage and residue management treatments in the field. Our results suggest that tillage-induced disturbance probably has a greater impact than food availability on earthworm populations in cool, humid agroecosystems.     

Supplemental saline drip irrigation applied at different growth stages of two bell pepper cultivars grown with or without mulch in non-saline soil

The effect of supplemental saline (2.5 dS m⁻¹) drip irrigation and black polyethylene mulch on two cultivars of bell peppers (Capsicum annuum L.) was investigated under field conditions using a randomized complete block design with split-split plot restriction. The research included six irrigation treatments (main plots): (i) non-saline irrigation control applied throughout growth (None), (ii) saline irrigation from transplanting until formation of the first fruit set (S1S2), (iii) saline irrigation from transplanting until appearance of the first flower and from first harvest to final harvest (S1S4), (iv) saline irrigation from appearance of the first flower to first harvest (S2S3), (v) saline irrigation from fruit set to final harvest (S3S4), and (vi) saline irrigation throughout growth (All); two mulch treatments (subplots): (i) black mulch and (ii) bare soil; and two bell pepper cultivars (sub-subplots): (i) Early Sunsation and (ii) Red Knight. Production of fully ripened fruits was higher in mulched plants regardless of saline irrigation treatments. In humid areas with non-saline soil, supplemental saline drip irrigation could be used with black polyethylene mulch to save water while maintaining fruit production.     

Water and Fertilizer Nitrogen Management to Minimize Nitrate Pollution from a Cropped Soil in Southwestern Quebec,Canada

Nitrate-N (NO₃ ^--N) pollution of water resources is a widely recognized problem. Water and nitrogen fertilizer are the two most important factors affecting NO₃ ^--N movement to surface and groundwater. Field trials were conducted from 1998 to 2000 growing seasons to investigate the combined impacts of water table management (WTM) and N fertilization rate on NO₃ ^--N concentration in the soil profile and in drain discharge. There were two water table treatments: free drainage (FD) with open drains at a 1.0 m depth from the soil surface and subirrigation (SI) with a target water table depth of 0.6 m below the soil surface, and two N fertilizer rates: 120 kg N ha^-1 (N₁₂₀) and 200 kg N ha^-1 (N₂₀₀) in a split-plot design. Compared to FD, SI reducedNO₃ ^--N concentration in the soil by up to 50% averaged over the two N rates. Concentrations of NO₃ ^--N in drainage water fromSI plots were lower than those from FD by 55 to 73%. These findings suggest that SI can be used as a means of reducing soil NO₃ ^--N pollution and drainage water NO₃ ^--N concentrations.     

Supplemental irrigation of bananas in St. Lucia

A trickle irrigation system was designed and installed on a small banana farm (0.5 ha). Various soil and crop characteristics were measured over a 2-year period in six irrigated and seven non-irrigated plots in a completely randomized design.Yield increases of 7.3 and 4.3% were measured in the plant and second ratoon crops, respectively. Irrigation significantly decreased the number of days to harvest and increased leaf production. Some problems were encountered in managing the water applications on the heavy, montmorillonitic clay soil.     

Effects of Stem-Injected Plant Growth Regulators, with or without Sucrose, on Grain Production, Biomass and Photosynthetic Activity of Field-Grown Corn Plants

Study of plant growth regulators (PGRs) through conventional foliar application or tissue culture or other organic materials has limitations. No previous study has examined the effects of long-term continuous addition of PGRs, with or without sucrose, to field-grown corn ( Zea mays L.) plants. A field study was conducted to determine the effects on corn plant growth and productivity during the grain-filling period of a continuous supply of PGRs, with or without sucrose, using a recently developed injection technique to deliver pressurized solutions through syringe needles sealed to the stem with latex. Our four PGRs (IAA, ABA, ethephon and salicylic acid) and a distilled water control, and two levels of sucrose (150 g l⁻¹ and a distilled water control) were injected into corn plants for 42 consecutive days during the grain-filling period. The plants injected with solutions not containing sucrose took up 42 ml more than those injected with sucrose-containing solutions. Corn plants injected with salicylic acid (SA) produced 9 % more grain yield than plants injected with no PGRs. The combination of SA and sucrose increased the photosynthetic rate by 42 % when compared with distilled water. Injection of ethephon resulted in an 11 % reduction in grain yield. Neither IAA nor ABA altered plant photosynthesis or productivity. Sucrose injection increased the dry weight of injected internodes and stover, and induced partial stomatal closure, although without any measurable effect on net photosynthetic rate. This study showed that stem injection makes possible the study of changes in plant physiology during grain-filling due to the effects of PGRs and metabolites administered continuously over protracted periods of time. It also demonstrated a previously undocumented stimulation of plant photosynthesis and grain yield by SA.     

Adapting the CROPGRO model for saline soils: the case for a common bean crop

Water scarcity and severe environmental degradation are causing water managers in the Fergana Valley, Uzbekistan to re-evaluate irrigation water use. Crop models could play an important role in helping farmers decide which systems (crops and irrigation technologies) are feasible. CROPGRO is a physiologically robust agronomic model, although the current version does not consider the effects of soil salinity on crop water use or growth. CROPGRO was modified to include a salinity response function and was tested for gypsiferous soils. A qualitative analysis of the model indicated the model performed as expected under a range of atmospheric, irrigation and crop tolerance scenarios. Model simulations compared very favourably for common bean (Phaseolus vulgaris) to results obtained in the greenhouse for yield and seasonal crop evapotranspiration with values of the Willmott agreement index (i) of 0.98 for both variables evaluated at different levels of salinity and deficit irrigation. Final biomass predictions were less satisfactory, although the modified model performed as well as the original model. The modified model was successfully tested with field data on common bean from an experiment in the Fergana Valley (i of 0.75 for ET and 0.74 for final yield), although the sensitivity of the model to a soil fertility function and relative nodule number made it difficult to assess the model performance.     

农田水位管理系统地下排水磷淋失实验研究

农田控制排水对减少土壤养分淋失、保护农田水环境具有重要作用。为探讨影响地下排水磷淋失量的要素,基于田间实验小区观测资料,统计分析了玉米作物生长期间农田水位管理系统运行对地下排水量和磷淋失量的影响,结果表明,与暗管自由排水系统相比,农田水位管理系统下的累积排水总量约减少1/3,但次地下排水磷淋失浓度和地下排水总磷累积淋失量均明显增高。农田水位管理系统下存在的土壤持续性饱和厌氧状态造成地下排水中氧化还原电位Eh的明显降低和pH值及可溶解性Mn和Fe浓度的显著增大,这或许是导致该系统地下排水磷淋失量明显高于暗管自由排水系统的主要影响因素。     

Denitrification and nitrous oxide to nitrous oxide plus dinitrogen ratios in the soil profile under three tillage systems

There is a growing interest in the adoption of conservation tillage systems [no-till (NT) and reduced tillage (RT)] as alternatives to conventional tillage (CT) systems. A 2-year study was conducted to investigate possible environmental consequences of three tillage systems on a 2.4-ha field located at Macdonald Research Farm, McGill University, Montreal. The soil was a sandy loam (0.5 m depth) underlain by a clay layer. Treatments consisted of a factorial combination of CT, RT, and NT with the presence or absence of crop residue. Soil NO₃^--N concentrations tended to be lower in RT than NT and CT tillage treatments. Denitrification and N₂O emissions were similar among tillage systems. Contrary to the popular assumption that denitrification is limited to the uppermost soil layer (0–0.15 m), large rates of N₂O production were measured in the subsurface (0.15–0.45 m) soil, suggesting that a significant portion of produced N₂O may be missed if only soil surface gas flux measurements are made. The N₂O mole fraction (N₂O:N₂O+N₂) was higher in the drier season of 1999 under CT than in 2000, with the ratio occasionally exceeding 1.0 in some soil layers. Dissolved organic C concentrations remained high in all soil depths sampled, but were not affected by tillage system.     

Paper submitted for the nineth international drainage workshop (ICID)

The environmental benefits of water table management (WTM), as a method to reduce nitrate pollution, are well known. However, there are few published studies on the effects of WTM on water use efficiency (WUE). This paper highlights the agronomic interest of WTM for increasing WUE of irrigated grain corn production. A field study was conducted in 2001 and 2002 at a large scale WTM research facility in Québec, Canada. The region experienced periods of drought during the two growing seasons. This study shows that, by keeping the water table at 0.80 m below the soil surface, there were on average 35% increases in grain corn yields, compared to conventional free drainage. The WUEs obtained with WTM (5.1 kg m⁻³ in 2001 and 7.1 kg m⁻³ in 2002) indicate that the method is generally more water efficient than conventional sprinkler and furrow irrigation. The WUE of WTM also compares well with that of water conservation methods such as alternate furrow irrigation and deficit sprinkler irrigation. Moreover, WTM requires low inputs in terms of equipment, energy, and labour, because it makes use of existing subsurface drainage systems, which are widespread in Eastern Canada due to the region's soils and climate, and because of its design, which does not necessitate high-pressure pumps and allows for automated management. Hence, WTM appears to be an interesting alternative to conventional irrigation methods due to its combined environmental and agronomical benefits.     

Application of geographic information systems in watershed management planning in St. Lucia

The use of geographic information systems (GIS) to develop conservation-oriented watershed management strategies on St. Lucia is presented. A soil loss model was executed within a GIS environment to evaluate agricultural management strategies in terms of soil loss on two agricultural watersheds. The GIS provided a fast and efficient means of generating the input data required for the model and allowed for easy assessment of the relative erosion hazard over the watersheds under the different land management options. The model predicted substantial declines in soil loss under conservation-oriented land management compared to current land management for both watersheds. The results of this study indicate that soil loss potential on the Soufriere watershed is approximately four times higher than on the Marquis watershed. This study represents the first attempt in the application of GIS technology to watershed conservation planning for St. Lucia. The procedures developed will contribute to the evolution of a decision support system to guide agricultural and forestry land planning in St. Lucia.