Productivity of Florida Springs: final report to Biology Branch, Office of Naval Research progress from December 31, 1955 to May 31, 1956

CONTENTS: Factors that control species numbers in Silver Springs, by James L. Yount. Study of the biomass of parasites in the stumpknockers, by Wanda Hunter. Macrophytic communities in Florida inland waters, by Delle N. Swindale. Comment in retrospect, by Howard T. Odum. (15pp.

A time for rainfed agriculture: Eleventh Coromandel Lecture

In this lecture a plea is made for the study and promotion of increased agricultural production and stabilization of crop yields in rainfed areas of India, based on experience gained by the author in different parts of the world and particularly at ICRISAT. The increasing pressure of population on land resources in India, and particularly the weather, makes it essential to get the maximum food production both from irrigated and rainfed areas. Out of 142 ha of cultivated land in India, about 108 mill ha depend on rainfed agriculture, accounting for 42% of foodgrains production. Average yields are low, generally below 800 kg/ha. It is possible to increase the yields by 50 to 100% with the existing technologies. The contribution of improved, input-responsive seeds and fertilizers, improved management of soil and rainfall, proper choice of cropping systems, supplementary irrigation and water harvesting in rainfed areas, and adoption of full packages of practices will enable modern agriculture and higher production and farm incomes to spread throughout the rainfed area

The Need And Prospects For Agrotechnology Transfer

Many people in the world today do not receive enough food, and the prospects for the future are depressing. The deficits in staple foods in the developing countries are likely to be three to four times as great in 1990 as they are today. There is need for more intensive use of soils, but there is already much concern about the deterioration of soils throug- h excessive and unwise use. Agricultural research can contribute significantly to the amelioration of these problems, but because research costs are high and increasing, efforts are needed to make agricultural research more efficient. Many small countries will not have the resources to make the magnitude of research effort needed to solve their own problems. In these dire circumstances, greater efforts need to be made to transfer agricultural technology from place to place and country to country. Presently it is being done mostly by trial and error, but more scientific approaches are being developed. Models that simulate biological processes and regression equations relating crop performance to input and sitefactor variables have great potential but only limited success to date, because of the magnitude of environmental site-factor constraints. Methods of analogous transfer have much greater immediate value. They are widely if casually used. They can be made more useful and more scientific if they are based upon the stratification of resource and environmental constraint variables, particularly of climates and soils. A methodology for systematic, analogous agrotechnology transfer now exists in the combination of soil survey, Soil Taxonomy, the benchmark soils concept, and the methods of soil survey interpretation. Some useful scientific proofs have been made of the transfer methodology over a global soils network, far exceeding in its geographic coverage the current possibilities of simulation or statistical methods. It is easy to see how the number of stations in the network can be increased through an International Benchmark Soils Network. The new methodology opens up the real possibility of technical communication and cooperation among the developing countries. It opens up the real possibility of increasing the efficiency of agronomic research. It opens up the need for countries to know their soils better and to strengthen their programs of soil survey interpretation. It opens up the possibilities for much greater and more effective use of soils information in the planning of agricultural development. An operating network of stations for agrotechnology transfer will not decrease the need for national agricultural research, because there is proof that transfer will not occur in the absence of local research capacity. Research in developed countries and in the international agricultural centers assists the transfer process, but does not replace the need for national research

A time for rainfed agriculture

In this lecture a plea is made for the study and promotion of increased agricultural production and stabilization of crop yields in rainfed areas of India, based on experience gained by the author in different parts of the world and particularly at ICRISAT. The increasing pressure of population on land resources in India, and particularly the weather, makes it essential to get the maximum food production both from irrigated and rainfed areas. Out of 142 ha of cultivated land in India, about 108 mill ha depend on rainfed agriculture, accounting for 42% of foodgrains production. Average yields are low, generally below 800 kg/ha. It is possible to increase the yields by 50 to 100% with the existing technologies. The contribution of improved, input-responsive seeds and fertilizers, improved management of soil and rainfall, proper choice of cropping systems, supplementary irrigation and water harvesting in rainfed areas, and adoption of full packages of practices will enable modern agriculture and higher production and farm incomes to spread throughout the rainfed areas

Coordinated optimization of visual cortical maps (I) Symmetry-based analysis

In the primary visual cortex of primates and carnivores, functional architecture can be characterized by maps of various stimulus features such as orientation preference (OP), ocular dominance (OD), and spatial frequency. It is a long-standing question in theoretical neuroscience whether the observed maps should be interpreted as optima of a specific energy functional that summarizes the design principles of cortical functional architecture. A rigorous evaluation of this optimization hypothesis is particularly demanded by recent evidence that the functional architecture of OP columns precisely follows species invariant quantitative laws. Because it would be desirable to infer the form of such an optimization principle from the biological data, the optimization approach to explain cortical functional architecture raises the following questions: i) What are the genuine ground states of candidate energy functionals and how can they be calculated with precision and rigor? ii) How do differences in candidate optimization principles impact on the predicted map structure and conversely what can be learned about an hypothetical underlying optimization principle from observations on map structure? iii) Is there a way to analyze the coordinated organization of cortical maps predicted by optimization principles in general? To answer these questions we developed a general dynamical systems approach to the combined optimization of visual cortical maps of OP and another scalar feature such as OD or spatial frequency preference.Comment: 90 pages, 16 figure

Self-organization and the selection of pinwheel density in visual cortical development

Self-organization of neural circuitry is an appealing framework for understanding cortical development, yet its applicability remains unconfirmed. Models for the self-organization of neural circuits have been proposed, but experimentally testable predictions of these models have been less clear. The visual cortex contains a large number of topological point defects, called pinwheels, which are detectable in experiments and therefore in principle well suited for testing predictions of self-organization empirically. Here, we analytically calculate the density of pinwheels predicted by a pattern formation model of visual cortical development. An important factor controlling the density of pinwheels in this model appears to be the presence of non-local long-range interactions, a property which distinguishes cortical circuits from many nonliving systems in which self-organization has been studied. We show that in the limit where the range of these interactions is infinite, the average pinwheel density converges to $\pi$. Moreover, an average pinwheel density close to this value is robustly selected even for intermediate interaction ranges, a regime arguably covering interaction-ranges in a wide range of different species. In conclusion, our paper provides the first direct theoretical demonstration and analysis of pinwheel density selection in models of cortical self-organization and suggests to quantitatively probe this type of prediction in future high-precision experiments.Comment: 22 pages, 3 figure

Coverage, Continuity and Visual Cortical Architecture

The primary visual cortex of many mammals contains a continuous representation of visual space, with a roughly repetitive aperiodic map of orientation preferences superimposed. It was recently found that orientation preference maps (OPMs) obey statistical laws which are apparently invariant among species widely separated in eutherian evolution. Here, we examine whether one of the most prominent models for the optimization of cortical maps, the elastic net (EN) model, can reproduce this common design. The EN model generates representations which optimally trade of stimulus space coverage and map continuity. While this model has been used in numerous studies, no analytical results about the precise layout of the predicted OPMs have been obtained so far. We present a mathematical approach to analytically calculate the cortical representations predicted by the EN model for the joint mapping of stimulus position and orientation. We find that in all previously studied regimes, predicted OPM layouts are perfectly periodic. An unbiased search through the EN parameter space identifies a novel regime of aperiodic OPMs with pinwheel densities lower than found in experiments. In an extreme limit, aperiodic OPMs quantitatively resembling experimental observations emerge. Stabilization of these layouts results from strong nonlocal interactions rather than from a coverage-continuity-compromise. Our results demonstrate that optimization models for stimulus representations dominated by nonlocal suppressive interactions are in principle capable of correctly predicting the common OPM design. They question that visual cortical feature representations can be explained by a coverage-continuity-compromise.Comment: 100 pages, including an Appendix, 21 + 7 figure