Not all fields, nor even portions of fields, have the same economically optimal corn plant density. However, until the recent introduction of precision farming, producers could not benefit from these accepted intrafield differences. This field study was conducted on 170 cooperating farmer fields throughout the Midwestern U.S. Corn Belt between 1987 and 1996 and consisted of over 42 000 individual experimental units. At each location, corn (Zea mays L.) was overplanted and thinned to 44 000 to 104 000 plants ha−1. The objective of our field research was to estimate the economic value, to the farmer, of variable rate seeding (VRS) as compared with uniform rate seeding (URS). We first estimated the correlation between field quality and economically optimal plant density. The economically optimal uniform plant density for the Midwest Corn Belt was 67 900 plants ha−1. For every tonne per hectare increase in site quality, as measured by yield potential, the predicted value of the site‐specific economically optimal plant density increased by approximately 1200 plants ha−1. We compared differences in revenues minus seed costs on four simulated fields. The value of VRS, ignoring the costs of VRS equipment and services, ranged from $12.83 ha−1 for farmers with VRS technology and full information to $0.15 ha−1 for farmers with VRS technology but only partial information. Profitable implementation of VRS will require detailed and expensive information regarding site characteristics, production inputs, and stochastic factors. Therefore, VRS will remain economically infeasible for most commercial corn growers until the cost of obtaining such information decreases considerably.

The goal of this research was to determine the potential for use of site-specific management of corn hybrids and plant densities in dryland landscapes of the Great Plains by determining (1) within-field yield variation, (2) yield response of different hybrids and plant densities to variability, and (3) landscape attributes associated with yield variation. This work was conducted on three adjacent fields in eastern Colorado during the 1997,-98, and-99 seasons. Treatments consisted of a combination of two hybrids (early and late maturity) and four plant densities (24,692, 37,037, 49,382 and 61,727 plants ha)1) seeded in replicated long strips. At maturity, yield was measured with a yield-mapping combine. Nine landscape attributes including elevation, slope, soil brightness (SB) (red, green, and blue bands of image), EC a (shallow and deep readings), pH, and soil organic matter (SOM) were also assessed. An analysis of treatment yields and landscape data, to assess for spatial dependency, along with semi variance analysis, and block kriging were used to produce kriged layers (10 m grids). Linear correlation and multiple linear regression analysis were used to determine associations between kriged average yields and landscape attributes. Yield monitor data revealed considerable variability in the three fields, with average yields ranging from 5.43 to 6.39 mg ha)1 and CVs ranging from 20% to 29%. Hybrids responded similarly to field variation while plant densities responded differentially. Economically optimum plant densities changed by around 5000 plants ha)1 between high and low-yielding field areas, producing a potential savings in seed costs of $6.25 ha)1. Variability in yield across the three landscapes was highly associated with landscape attributes, especially elevation and SB, with various combinations of landscape attributes accounting for 47%, 95%, and 76% of the spatial variability in grain yields for the 1997,-98, and-99 sites, respectively. Our results suggest site-specific management of plant densities may be feasible.

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Nitrogen fertilization and irrigation practices can affect durum [Triticum turgidum subsp. durum (Desf.) Husn.] grain quality, especially protein content. The purpose of this study was to determine if irrigation frequency during grain fill influences the effectiveness of N applied near anthesis in increasing durum grain quality. A field study was conducted at Maricopa, AZ on a Casa Grande sandy loam soil (fine‐loamy, mixed, superactive, hyperthermic, Typic Natrargid). Durum was grown with recommended amounts of N fertilizer until anthesis when 0, 3.4, and 6.7 g N m−2 were applied and irrigation based on 30, 50, and 70% depletion of plant‐available soil water was initiated. Irrigation during grain fill had no effect on grain yield or grain quality except in 1996, when irrigating at 30, 50, and 70% depletion resulted in hard vitreous amber counts (HVAC) of 813, 870, and 934 g kg−1, respectively. Nitrogen application near anthesis of 0, 3.4, and 6.7 g N m−2 resulted in grain protein contents of 115, 127, and 140 g kg−1 in 1995 and 132, 141, and 151 g kg−1 in 1996, respectively. Nitrogen application near anthesis increased grain protein yield and HVAC in both years of the study and increased grain yield, grain volume weight, and kernel size in 1995. The results of this study suggest that N fertilizer application near anthesis has a primary influence on durum quality and that effects of irrigation frequency during grain fill are inconsistent or relatively minor.

No abstract

Biomedical micro implants are used as neural prostheses to restore body functions after paraplegia by means of functional electrical stimulation (FES). Polymer electronic technology offers the potential to integrate flexible electronic circuits on microelectrodes in order to overcome the limit of traditional FES systems. This paper describes an approach of flexible organic transistors in order to develop a flexible biomedical micro implant for FES use. Polyimide shows excellent biocompatibility and biostability properties for flexible multi-channel microelectrodes in neural prosthetics application (Stieglitz et al 1997 Sensors Actuators A 60 240–3). Therefore, it was used as a flexible substrate on which polymer transistors have to be integrated. Gold or platinum was sputtered as the gate, drain and source. In this paper polyimide has been investigated as a gate isolator because of its high flexibility and biocompatibility. Polyimide was spin coated and imidized at different temperatures and times. Pentacene (C14H22) was evaporated at UHV and 75 °C substrate temperature as an active layer in an organic field effect transistor (OFET). Plasma activation and self-assembled monolayer surface modification were used to advance the electrical properties of organic transistors. The whole transistor was encapsulated in parylene C that was evaporated at room temperature using a standard Gorham system (Gorham 1966 J. Polym. Sci. A-1 4 3027–39). Investigation of the electrical properties of the OFET using polyimide as the isolator led to promising results.

In arid regions of the U.S., high rates of water and N input are commonly used for cauliflower production. Production of cauliflower (Brassica olearacea L. var. botrytis L.) High rates of water and N input, and rapid rates of in the southwestern U.S. is highly dependent on inputs of water and N fertilizer to achieve optimum yields and quality. Subsurface drip nitrification typical of thermic and hyperthermic soils, irrigation offers what is likely the ultimate in control of the plant can contribute to increased production costs and losses root zone for crop production. However, the water and N-response of water and N. Therefore, accurate guidelines for water characteristics of subsurface drip-irrigated cauliflower have not preand N management for drip-irrigated cauliflower are viously been reported. Three field experiments were conducted in needed. However, management practices that increase southern Arizona in 1993-1996. The objectives were to determine: water and N-use efficiency must also be economically (i) an optimum range of soil water tension for subsurface drip-irrigated feasible. cauliflower, (ii) the effects and interactions of water and N fertilizer Total N uptake by cauliflower ranges from 70 to 260 on crop yield and quality, and (iii) seasonal and daily N uptake for kg ha Ϫ1 in whole plants and 40 to 125 kg ha Ϫ1 in the high-yielding cauliflower. The experiments were randomized comharvested portion of plants (Stivers et al., 1993). In Ariplete block factorial with three irrigation regimes (low, medium, high), four N rates (60-600 kg N ha Ϫ1), and four replications. Irrigation was zona, growers generally apply 224 to 370 kg N ha Ϫ1 (U.S. applied daily to maintain target soil water tensions and all N was Department of Agriculture, 1991), although recomapplied by fertigation. With respect to marketable yield, curd weight, mended amounts are somewhat lower (Doerge et al., and curd diameter, the optimum soil water tension was approximately 1991). Cauliflower is an initially slow-growing crop that 10 to 12 kPa in this sandy loam soil during the 3 years. Marketable takes up little N in its first 60 d of growth; 90% or more yields across all treatments ranged from Ͻ5 to Ͼ30 Mg ha Ϫ1. Yields of its total N accumulation may occur during the final and quality were generally more responsive to N rate than to irrigation 50 to 60 d preceding harvest (Welch et al., 1987). Cauliand showed significant irrigation by N rate interactions during 2 of the flower is highly responsive to N fertilizer inputs and is 3 years. At equivalent N rates, excessive irrigation generally resulted in rarely negatively affected by excessive N applications lower yields and quality. Cauliflower accumulated up to 250 kg N (Stivers et al., 1993). ha Ϫ1 in the aboveground biomass and N-uptake fluxes were as high as 5 kg N ha Ϫ1 d Ϫ1 at the 12-leaf to folding growth stage.

This paper reports on the design, in vitro and in vivo investigation of a flexible, lightweight, polyimide based implantable sieve electrode with a hybrid assembly of multiplexers and polymer encapsulation. The integration of multiplexers enables us to connect a large number of electrodes on the sieve using few input connections. The implant assembly of the sieve electrode with the electronic circuitry was verified by impedance measurement. The 27 platinum electrodes of the sieve were coated with platinum black to reduce the electrode impedance. The impedance magnitude of the electrode sites on the sieve (geometric surface area 2,200 microm(2)) was |Z(f=1kHz)| = 5.7 kOmega. The sieve electrodes, encased in silicone, have been implanted in the transected sciatic nerve of rats. Initial experiments showed that axons regenerated through the holes of the sieve and reinnervated distal target organs. Nerve signals were recorded in preliminary tests after 3-7 months post-implantation.