Windbreaks in North American agricultural systems

Agroforestry Systems - Windbreaks are a major component of successful agricultural systems throughout the world. The focus of this chapter is on temperate-zone, commercial, agricultural systems in...     

Influences of trees on abundance of natural enemies of insect pests: a review

In this article we review the use of natural enemies in crop pest management and describe research needed to better meet information needs for practical applications. Endemic natural enemies (predators and parasites) offer a potential but understudied approach to controlling insect pests in agricultural systems. With the current high interest in environmental stewardship, such an approach has special appeal as a method to reduce the need for pesticides while maintaining agricultural profitability. Habitat for sustaining populations of natural enemies occurs primarily at field edges where crops and edge vegetation meet. Conservation and enhancement of natural enemies might include manipulation of plant species and plant arrangement, particularly at these edges; and consideration of optimum field sizes, number of edges, and management practices in and near edges. Blending the benefits of agricultural and forestry (windbreak) systems is one promising approach to field edge management that has additional benefits of wind protection and conservation of desirable wildlife species.Journal series 10549 of the Agriculture Research Division, University of Nebraska-Lincoln. This material was prepared with the support of USDA Agreement 91-COOP-1-6592 for the USDA/EPA Program, Agriculture in Concert with the Environment. Any opinions, findings, conclusions or recommendations expressed herein do not necessarily reflect the views of the US Department of Agriculture or the US Environmental Protection Agency.     

Composition and structure of the venus atmosphere: results from pioneer venus

Results from the Pioneer Venus sounder probe neutral mass spectrometer indicate that there is no difference in the isotopic ratios of carbon and oxygen between Venus and Earth to within +/- 5 percent. The mixing ratio of nitrogen is 3.5(+3)(-2) percent with an isotopic ratio within 20 percent of that of Earth. The ratio of argon-36 to argon-40 is 85 percent, and the ratio of argon-38 to argon-36 is 20 percent. The mixing ratios of argon-36 and argon-40 are approximately 40 and 50 parts per million, respectively, with an error of about a factor of 2 (mainly toward a lesser amount) resulting from uncertainty in the response of the ion pump to rare gases. Hydrogen chloride cannot account for more than a few percent of the 36 mass peak, and therefore the large excess of primordial argon is a reasonable conclusion. The ratio of neon-20 to argon-36 of 0.5 +/- 0.3 is definitely terrestrial in character rather than solar. These results indicate that there is a large excess of all primordial noble gases on Venus relative to Earth. There appears to be a considerably higher abundance of sulfur compounds below 20 kilometers than in or above the main cloud layer. The 32 and 60 mass peaks show a sharp increase below 22 kilometers, indicating the possible production of sulfur and carbon oxysulfide (COS) at the expense of sulfur dioxide.     

Iron deficiency in wheat grown on the southern plains

Extensive areas of chlorotic winter wheat (Triticum aestivun L.) were observed on calcareous soils in western Oklahoma. Spraying severely chlorotic wheat with ferrous sulfate (FeSO₄) resulted in greening within a week and doubled herbage yield a month later. Intensive grazing of wheat prior to jointing induced no to severe chlorosis in 33 wheat cultivars tested over three years. After peak intensity in early April, the chlorosis diminished and was not visible when the wheat was fully headed in May. Overall, we believe increased iron (Fe) deficiency in wheat on the Southern Plains is due to increased use of Fe‐inefficient cultivars and stress induced by grazing. Wheat cultivars less susceptible to Fe deficiency are commercially available.