Runoff from typical urban and suburban landscapes may contain significant levels of nitrogen, phosphorus, and a broad spectrum of various pesticides (mainly herbicides and insecticides) due to excessive application rates of these chemicals and high irrigation requirements of most commonly used landscape plant species. Preliminary water quality data (runoff) from a comparative study of 20 microwatersheds using 4 different levels of maintenance, show reductions in these types of pollutants in runoff for microwatersheds planted to resource efficient plants. Utilization of plants indigenous to an ecoregion (and other resource efficient plants) in landscape design and management allows considerable reduction in inputs from fertilizer, water, and pesticides. This results in lower pollutant concentrations in runoff and is estimated to result in lower total pollutant loadings from such systems. Installation of native or resource efficient plants in new developments (commercial and residential) and replacement of existing landscapes with these plants as older plants die or neighborhoods are updated could provide cities and suburban areas with a cost-effective, low-maintenance, and aesthetically-pleasing pollution control technology. Data from the comparative study should provide municipalities charged with meeting the new requirements of the National Pollutant Elimination Discharge System with a way to compare the pollution prevention effectiveness of resource-efficient landscapes with more traditional structural urban runoff controls.

Decomposition of sorghum [Sorghum bicolor (L.) Moench] and wheat (Triticum aestivum L.) plant residues can immobilize eno~.gh surface-aJlplied N to cause a deficiency in successive winter wheat crops. This experiment examined the effects of conventional and mto-till grain sorghum and wheat residues on N requirements of dryland winter wheat. Field experiments conducted from 1987-1991 on an Austin silty clay (fine-silty, carbonatic, thermic Udorthentic Haplusloll) soil included sorghum and wheat residue treatments with conventional till (<:T), no-till (NT), and residue removal (RR). All resid11e plots received four preplant N rates (0, 45, 90, and 135 kg N ba-'), with subplots planted to three winter wheat cultivars in 198~1 and 1989, and two cultivars in 1990 and 1991. Grain and stover yields were significantly lower when wheat followed sorghum than u11der continuous wheat. Wheat grain yields at N application rates < 90 kg ba-' were 39% lower in NT plots vs. CT plots, 5% lower in CT plots compared with yields in RR plots, and 39% lower in sorgbum-wbeat n1tation compared with continuous wheat. Wheat N uptake at N application rates <:90 kg ba-• was 41% lower in NT plots vs. N uptake in CT plots, 10% lower in CT plots vs. N uptake in U~ plots, and

Much of the N applied to rainfed winter wheat (Triticum aestivum L.) is topdressed as granular fertilizer in late winter or early spring after growers evaluate over‐winter survival and potential economic returns from N fertilization. Information is needed to determine the optimum timing for efficient use of topdressed N by winter wheat. This study evaluated the effect of three rates (0, 40, and 80 lb N/acre) of ammonium nitrate on winter wheat grain yield, N uptake, grain protein, and net income when topdressed at or near planting through heading (1 April) on silty clay and clay soils. Field experiments were conducted at five different sites during the 1985, 1987, 1988, 1991, and 1992 winter wheat growing seasons on Udorthentic Haplustoll and Udic Pellustert soils located in the North Texas Blackland. From 1985 through 1992, topdress applications were timed at planting, jointing (Feekes 6), booting (Feekes 10), and heading (Feekes 10.5) winter wheat growth stages. Maximum grain yields (56–61 bu/acre) resulted from single N topdressings of 40 lb/acre at jointing, 80 lb/acre applied at planting through jointing, or split applications of 40 lb/acre at planting and jointing. Grain protein concentrations were highest (15.3%) when N was topdressed at jointing and booting compared with planting and heading applications (14.9%). Highest grain N uptake (108 lb/acre) occurred with single N topdressings of 80 lb/acre from planting through booting stages, and with split N application. Optimum economic winter wheat grain yields were obtained with single, adequate N topdressings made at or near planting through prebooting stage (1 March). Fertilizer‐N topdressed following booting resulted in grain yields that were 13 to 19% lower than observed with N topdressed prebooting. This was attributable to low available soil moisture from March through April. Water stress after booting increased winter wheat vegetative growth at the expense of grain yield, and probably reduced ammonium nitrate movement into the soil‐plant‐root zone. Research Question Granular N fertilizer topdressing is a safe, economical application method for rainfed winter wheat production. Research is lacking on the effectiveness of single preplant through late‐spring and split N fertilizer topdressings at more than one application rate for rainfed winter wheat. The objective of this study was to evaluate the effect of three N rates (0, 40, and 80 lb/acre) topdressed from planting through grain ripening (Feekes growth stage 11.1) on winter wheat grain yield and protein content. Literature Summary Nitrogen applications should be timed when crop use of N is high. Winter wheat N uptake is most rapid from tillering (Feekes 5) through booting (Feekes 10) developmental growth stages with 80% of the total accumulation occurring before grain filling. Research has shown N applications after booting may not become positionally available to plant roots early enough to benefit vegetative growth or may contribute to excessive late‐season vegetative growth at the expense of grai...

Experiments were conducted under irrigated, subtropical conditions to evaluate the influence of previous crop on NO3‐N distribution in the soil profile and subsequent response by cotton (Gossypium hirsutum L.) and grain sorghum (Sorghum bicolor (L.) Moench.) to applied N. Responses to N were obtained with cotton and grain sorghum if planted immediately after cabbage (Brassica oleracea var. capitata), but responses to N were small or non‐existent if the area was fallow from September until March. Fall and winter temperatures are warm enough that N mineralization allows accumulation of NO3‐N in the soil profile and may preclude a response from application of N.

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