In order to reduce nutrient losses and soil erosion in the United States Upper Midwest following soybean [Glycine max (L.) Merr.], cover crops can be intersown into standing soybean. The objective of this study was to determine the establishment of intersown cover crops and their impacts on a soybean-wheat (Triticum aestivum L.) rotation. Four cover crops, winter camelina [Camelina sativa (L.) Crantz], winter pea [Pisum sativum ssp. arvense (L.) Poir], winter rye (Secale cereale L.), and radish (Raphanus sativus L.), were directly sown into the ground at the R4 and R6 stages of soybean at two locations, Prosper and Fargo, ND in 2016-2018. Results indicated intersowing cover crops have no impact on soybean yield, can produce above ground biomass which ranged from 0.44 to 3.04 Mg ha-1, and show potential to mitigate soil nitrate losses in areas that grow soybean as a cash crop.

Over 18 years after the democratic government took power in South Africa, environmental changes relevant to the land reform policies are taking place because of unintended consequences of land reform policy. This study aimed at investigating the effects of the South African land reform policy on land use and land cover change on a land restitution project in Makotopong, Limpopo province, South Africa. The study used remote sensing techniques through the analysis of Landsat TM images acquired in 1994 and 2007 to produce landscape maps and derive land cover change. Statistics deriving the nature of the decline in the general condition of the land restitution project gave an insight into the kind of landscape transformation that has taken place before and after land restitution program. Quantification of land cover classes have shown a decline in post-transfer activities with a decline in agricultural productivity, as illustrated by the decline in area covered by agricultural crops (showing a decline from 78.03 ha in 1994 to 20.43 ha in 2007). The study recommends that spatial data analysis through remote sensing procedures should form the information base in monitoring and evaluating the land reform projects. Results of this study demonstrated that quantification of the changes in land use and land cover types can be very useful in deriving the nature of the general environmental and social condition of the land reform project. / Thesis (M. Sc (Geography) North-West University, Mafikeng Campus, 2012

No description available.

In this thesis, we focus on the study of dependent arcs of acyclic orientations of graphs. Given an acyclic orientation D of G, Edelman cite{West} defined an arc to be {em dependent} if its reversal creates a cycle in D; otherwise, it is independent. Let d(D) and i(D) be the numbers of dependent arcs and independent arcs in D, respectively. And, let d_{max}(G)(d_{min}(G)) and i_{max}(G) (i_{min}(G)) be the maximum (minimum) numbers of dependent arcs and independent arcs over all acyclic orientations of G, respectively. Edelman cite{Fisher} showed that if G is connected, then d_{max}(G)=||G||-|G|+1. A graph G is said to satisfy the {em interpolation property} (or G is fully orientable) if $G$ has an acyclic orientation with exactly k dependent arcs for every k with d_{min}(G) leq k leq d_{max}(G). West established the interpolation property for complete bipartite graphs cite{West}. We obtain the minimum numbers of dependent arcs of the outerplane graphs and show that the outerplane graphs satisfy the interpolation property. Let N(G) be the set { i(D)| D is an acyclic orientation of G }. N(G) is called the independent-arc spectra of G. For complete k-partite graphs G, we obtain i_{max}(G) and discuss the independent-arc spectra for some classes. On the other hand, we consider the cover problem. A cover graph is the underlying graph of the Hasse diagram of a finite partially ordered set. The cover problem is that whether a given graph is a cover graph. It is easy to see that a graph G is a cover graph if and only if d_{min}(G)=0. We show that the generalized Mycielski graphs M_m(C_{2t+1}) of an odd cycle, Kneser graphs KG(n,k), and Schrijver graphs SG(n,k) are not cover graphs when m geq 1, t geq 1, k geq 3 and n geq 2k+2.

Thesis (doctoral)--Techn. Universität, Dresden, 2002.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 73-77). Also available via the Internet.

Thesis (Master of soil science)--Washington State University, December 2006. / Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 68-74). Also available on the World Wide Web.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Kathryne L. Everts and Jeffrey J. Fuhrmann, Dept. of Plant and Soil Science. Includes bibliographical references.

Master of Science / Department of Agronomy / Nathan O. Nelson / Phosphorus (P) loss from non-point agricultural sources has been identified as a main contributor to degraded surface water quality throughout the United States. Excessive P inputs to surface waters can lead to eutrophication, increased water treatment costs, and negative health impacts. Therefore, agricultural best management practices (BMP) that promote water quality, through minimizing P loss, must be identified. Studies outlined in this thesis aim to determine the impacts of cover crops and P fertilizer placement on P loss in surface runoff and nutrient cycling in a no-till corn (Zea mays)-soybean (Glycine max) rotation and provide insight into how cover crop species selection and termination method affects potential P loss from crop tissue. The first study examined combined effects of cover crop and P fertilizer placement on total P, dissolved reactive P (DRP) and sediment losses in surface runoff from natural precipitation events. This large-scale field study was conducted near Manhattan, Kansas, at the Kansas Agricultural Watershed (KAW) Field Laboratory during the 2016 and 2017 cropping years. Two levels of cover crop [no cover crop (NC) and cover crop (CC)] and three levels of P fertilizer management [no P (CN), fall broadcast P (FB), and spring injected P (SI)] were used. Flow-weighted composite water samples were collected from precipitation events generating greater than 2.0 mm of surface runoff. Results from this study found the CC treatment increased DRP losses compared to NC in both cropping years; however, CC reduced sediment loss by over 50% compared to NC. Application of P fertilizer increased DRP losses compared CN in both cropping years, although SI resulted in lower quantities of DRP loss compared to FB. In addition, this study found that CC reduced biomass and yield of corn compared to NC and therefore decreased nutrient uptake, removal, and deposition during the 2017 cropping year. However, no negative impacts of CC on biomass or yield were observed during the 2015 (corn) and 2016 (soybean) cropping years. Application of P fertilizer increased the concentration of Melich-3 P and total P in the top 0-5 cm of soil compared to CN; however, no differences between P fertilizer management practice were observed for concentrations of Melich-3 P at 5-15 cm. A greenhouse-based study determined the impacts of cover crop species (brassica, grass, and legume), termination method (clipping, freezing, and herbicide), and time after termination (1, 7, and 14 days after termination) on total P and water-extractable P (WEP) release from cover crop biomass. Freezing increased WEP concentration of crop tissue by more than 140% compared to clipping and herbicide. Additionally, at 7 and 14 days after termination, both concentration of WEP and fraction of WEP compared total P increased compared to 1 DAT. Findings from these studies suggest the use of cover crops may unintentionally result in greater DRP losses in surface runoff. However, addition of a cover crop can dramatically reduce erosion losses. In addition, cover crop species selection can directly impact the quantity of P being taken up and released by crop tissue. Understanding the impact of crop species selection may help create new BMPs which aim to reduce P loss.