作物生产给植物提供真正所需

精准农业的目的就是要按照作物生长需要有针对性地进行栽培管理。该文从耕种方式、播种方式、施肥方式以及农田作业轨迹方面出发,介绍了现行一些精准农业发展情况,同时指出了所面临的问题及发展方向。      

Strip-tillage effect on seedbed soil temperature and other soil physical properties

The no-tillage system is perceived as having lower soil temperatures, wetter soil conditions, and greater surface penetration resistance compared with conventional and other conservation tillage systems. Concerns associated with the effect of the no-tillage system on certain soil physical properties (i.e. soil temperature, moisture, and compaction) prompted this study to evaluate the effect of an alternative tillage system, strip-tillage, on these physical properties, compared with chisel plow and no-tillage systems. The study was conducted on two Iowa State University research and demonstration farms in 2001 and 2002. One site was at the Marsden Farm near Ames, where the soils were Nicollet loam (Aquic Hapludolls) and Webster silty clay loam (Typic Haplaquolls). The second site was at the Northeast Research and Demonstration Farm near Nashua, where the soils were Kenyon loam (Typic Hapludolls) and Floyd loam (Aquic Hapludolls).Soil temperature increased in the top 5 cm under strip-tillage (1.2–1.4 °C) over no-tillage and it remained close to the chisel plow soil temperature. This increase in soil temperature contributed to an improvement in plant emergence rate index (ERI) under strip-tillage compared with no-tillage. The results show no significant differences in soil moisture status between the three tillage systems, although the strip-tillage soil profile has slightly greater moisture content than chisel plow. Moisture content through the soil profile particularly at the lower depths under all tillage treatments was greater than the plant available water (PAW). However, the changes in soil moisture storage were much greater with strip-tillage and chisel plow than no-tillage from post-emergence to preharvest at 0–30 and 0–120 cm. It was observed also that most change in soil moisture storage occurred between post-emergence and tasseling. Penetration resistance was similar for both strip-tillage and no-tillage, but commonly greater than chisel plow. In general, the findings show that strip-tillage can contribute effectively to improve plant emergence, similar to chisel plowing and conserve soil moisture effectively compared with no-tillage.     

Antecedent water content effects on runoff and sediment yields from two Coastal Plain Ultisols

The highly weathered, low-carbon, intensively cropped, drought-prone Coastal Plain soils of Georgia are susceptible to runoff and soil loss, especially at certain times of the year when soil water contents are elevated. We quantified the effects of antecedent water content (AWC) on runoff (R) and sediment (E) losses from two loamy sands managed under conventional- (CT), strip- (ST), and/or no-till (NT) systems. Two AWC treatments were evaluated: field moist (FM) and pre-wet (PW), created with and without post pesticide application irrigations (∼12 mm of water added with the rainfall simulated over 30 min) for incorporation. Treatments (5) evaluated were: CT + FM, CT + PW, ST + FM, ST + PW, and NT + PW. Field plots, each 2-m × -3 m, were established on each treatment. Each 6-m² field plot received simulated rainfall at a variable rainfall intensity (I_v) pattern for 70 min (site 1) or a constant rainfall intensity (I_c) pattern for 60 min (site 2; I_c = 50.8 mm h⁻¹). Adding ∼12 mm of water as herbicide incorporation increased AWCs of the 0-2 (3-9-fold) and 2-15 (23-117%) cm soil depths of PW plots compared to existing field moist soil conditions. Increase in AWC increased R (as much as 60%) and maximum R rates (as much as 62%), and decreased E (at least 59%) and maximum E rates (as much as 2.1-fold) for corresponding tillage treatments. Compared to CT plots, ST and NT plots decreased R (at least 2.6-fold) and maximum R rates (as much as 3-fold), and decreased E (at least 2.7-fold) and maximum E rates (at least 3.2-fold). Runoff curves for pre-wetted CT and ST plots were always higher than corresponding FM curves, whereas E curves for field moist CT and ST plots were always higher than corresponding PW curves. Changes in AWC and tillage affected detachment and transport processes controlling runoff and sediment yields. A more accurate measure of rainfall partitioning and detachment and transport processes affecting R and E losses was obtained when commonly occurring field conditions (increased AWC with irrigation; I_v pattern derived from natural rainfall; commonly used tillage systems) were created and evaluated.     

Precise tillage systems for enhanced non-chemical weed management

Soil and residue manipulation can assist weed management by killing weeds mechanically, interfering in weed lifecycles, facilitating operations and enhancing crop establishment and growth. Current tillage systems often compromise these functions, resulting in heavy reliance on herbicides, particularly in no-till systems. Herbicides are an exhaustible resource, so new approaches to merge soil conservation and non-chemical weed management are needed. This paper broadly reviews various preventive and curative non-chemical weed management tactics. It also demonstrates how innovations can be derived from functional requirements of weed management operations, and from biological processes and weaknesses in weed's lifecycles. Mechanical weeding and enhancement of weed seed mortality are highlighted as examples. Major limitations with mechanical weeding include limited weed control in crop rows at early vulnerable crop stages, weather-dependent effectiveness, and difficulties in handling crop residues. Precise steering and depth control, improved seedbed friability and lighter tractors or controlled traffic could bring considerable improvements. To expose weed seeds to predators, position them for fatal germination, viability loss or low emergence may require completely different soil displacement patterns than those of current implements and systems. Controlled traffic and precise strip tillage offer good opportunities for implementing these weed management strategies in minimum-tillage systems.