Answer:
Fertilizing prior to soybean production is not a common practice in Iowa. Nutrient deficiencies in soybean are rare and current recommendations in Iowa are to apply additional nutrients only if soil tests indicate that a specific nutrient is at a low concentration or if deficiencies are identified in the field. Deficiencies are rare even though the soybean plant requires more nitrogen than corn, and as a result can fix up to 50% of its own nitrogen. In central and north central Iowa, the nutrient most often limiting is iron, and this deficiency is only found in calcareous soils with high pH where the iron is bound tightly to the soil. When nutrients are limited, processes such as water transport, photosynthesis, and protein, oil, and carbohydrate production do not occur at proper rates and growth and yield development decrease. Even though nutrients are usually not a limiting factor in production systems it is worthwhile to understand and identify deficiency symptoms so that they can be corrected during the season or in following years.
Crop production is often restricted by the availability of essential mineral elements. For example, the availability of N, P, K, and S limits low-input agriculture, the Phyto availability of Fe, Zn, and Cu limits crop production on alkaline and calcareous soils, and P, Mo, Mg, Ca, and K deficiencies, together with proton, Al and Mn toxicities, limit crop production on acid soils. Since essential mineral elements are acquired by the root system, the development of crop genotypes with root traits increasing their acquisition should increase yields on infertile soils. This paper examines root traits likely to improve the acquisition of these elements and observes that, although the efficient acquisition of a particular element requires a specific set of root traits, suites of traits can be identified that benefit the acquisition of a group of mineral elements. Elements can be divided into three Groups based on common trait requirements. Group 1 comprises N, S, K, B, and P. Group 2 comprises Fe, Zn, Cu, Mn, and Ni. Group 3 contains mineral elements that rarely affect crop production. It is argued that breeding for a limited number of distinct root ideotypes, addressing particular combinations of mineral imbalances, should be pursued.