Nutrient Content of Sorghum Leaves and Grain as Influenced by Long-Term Crop Rotation and Fertilizer Treatment

The objective of this research was delineation of longterm crop rotation and fertilizer influence on levels of N, P, K, Ca, and Mg in sorghum leaves and grain. Continuous farming practices may introduce gradual departures in the prevailing initial biological, chemical, and physical characteristics of the plant root environment, thereby altering soil productivity characteristics. These chnges, as they alter nutrient composition and yield of crops, can be documented from long-term field experiments maintained under continuous farming and fertilization programs. The treatments featured continuous versus rotations of grain sorghum (Sorghum vulgare), wheat (Triticum aestivum) and cotton (Gossypinm hirsutum) with and without fertilizer. Most treatments have been applied annually for over 20 years. Fertilization of grain sorghum predominantly consisted of N and P at rates of 45 and 20 kg/ha, respectively, in field plots on a Houston Black clay soil (fine montmorillonitic thermic family of Udic Pellusterts). Apart from some selective positive influence on sorghum leaf N, leaf P and leaf K, the crop rotational effect on leaf composition was considered inconclusive. Generally, crop rotation did result in larger grain production with fertilized as well as with unfertilized sorghum. Levels of sorghum leaf N, leaf P, leaf K, and leaf Ca were mostly higher in plants receiving fertilizer than in checks. Grain sorghum leaf N, leaf P, leaf Ca, and leaf Mg percentages decreased, increased, or remained nearly constant during the interval from plant booting to half bloom. Sorghum leaf K percentages generally decreased from booting to half bloom. Fertilizer increased grain protein percentage and grain yield. Yet, high rates of fertilizer are not usually recommended in the Texas Blackland Prairie because of frequent soil moisture depletion prior to or at grain formation. Sorghum leaf composition, grain protein level and grain yield portrayed noticeable response to applied cattle manure plus fertilizer N and P. As the measurable response to fertilizer P was below expectation, its significance on longterm maintenance of balanced soil fertility remains an important consideration.