Dryland Winter Wheat Yield, Grain Protein, and Soil Nitrogen Responses to Fertilizer and Biosolids Applications

Applications of biosolids were compared to inorganic nitrogen (N) fertilizer for two years at three locations in eastern Washington State, USA, with diverse rainfall and soft white, hard red, and hard white winter wheat (Triticum aestivum L.) cultivars. High rates of inorganic N tended to reduce yields, while grain protein responses to N rate were positive and linear for all wheat market classes. Biosolids produced 0 to 1400？kg？ha？1 (0 to 47%) higher grain yields than inorganic N. Wheat may have responded positively to nutrients other than N in the biosolids or to a metered N supply that limited vegetative growth and the potential for moisture stress-induced reductions in grain yield in these dryland production systems. Grain protein content with biosolids was either equal to or below grain protein with inorganic N, likely due to dilution of grain N from the higher yields achieved with biosolids. Results indicate the potential to improve dryland winter wheat yields with biosolids compared to inorganic N alone, but perhaps not to increase grain protein concentration of hard wheat when biosolids are applied immediately before planting. 1. Introduction Biosolids are an effective and relatively safe source of nitrogen (N) for dryland wheat production [1–3]. Applied at agronomic rates, biosolids can supply sufficient N to maximize yield, as well as a host of other nutrients that can benefit crops in a rotational sequence [4, 5]. Determining appropriate agronomic application rates is paramount in balancing nutrient (mainly N) needs of wheat without increasing the risk of nitrate (NO3？) leaching. Considerable research has been devoted to this subject [3, 5]. In the inland Pacific Northwest (PNW) USA, soft white winter wheat is the predominant crop grown on over 2.75 million ha of mainly dryland (rainfed) cropland [6]. The majority of this wheat is exported and used to make unleavened products such as flat breads, noodles, and cakes [7]. Low-grain protein concentration (<10%) is desirable when producing unleavened products. High-grain protein concentration in soft white winter wheat has been a problem in the PNW due, in part, to high soil N levels [7]. Previous biosolids research in this area has shown that agronomic applications at or above rates required to maximize yield may produce undesirably high grain protein concentrations in soft white winter wheat [3, 5]. While high grain protein concentration is detrimental for soft wheat end uses, high protein is desirable in hard red and white winter wheats, with optimum targets of approximately 11.5 and 12.5%,