Max D. Clegg

Photosynthesis Light Sensor and Meter

An improved light sensor with a spectral response based on photon absorption between 400 and 700 nm was developed for both field and environmental chamber use. The indicated sensor response was selected because it approximates the photosynthetic response of plants for which data are available. A silicon photo cell with high response in the visible range was used as a sensor. The spectral response was controlled by use of a Kodak Gelatin Wratten Filter. A visible bandpass interference filter produced a sharp cutoff at 700 nm. Heat—absorbing glass eliminated transmission beyond 1,000 nm, and a diffusing plastic and filters were mounted in a miniaturized cosine—corrected head that was fitted with a collimating system to eliminate spectral shifts which arise when light enters the interference filter at oblique angles. Error calculations indicate that under sun—and—sky radiation and various artificial light sources the errors are smaller than those associated with available standard calibration lamps. The device also includes a battery—operated meter circuit suitable for making measurements over a wide range of intensities.

Rotation effect on sorghum response to nitrogen fertilizer under different rainfall and temperature environments

Cropping sequence effects on sorghum (Sorghum bicolor L. Moench) response to nitrogen fertilizer under different rainfall and temperature regimes were evaluated in eastern Nebraska. The Standardized Precipitation Index (SPI) and temperature Z-scores were used to characterize the 18-yr cropping period into eight sets of contrasting cropping environments. Mean sorghum yields ranged from 4050 to 6260 kg/ha in continuous cropping, and from 5130 to 7120 kg/ha in rotation with soybean (Glycine max), a significant increase with crop rotation. Yields were lower in dry years with hot April temperatures than in dry years with cool April temperatures. Hot April temperatures improved yields in wet years. April temperature did not affect yield if a wet pre-season was followed by a dry cropping season. Sorghum responded more to fertilizer N in dry than in wet years, reflecting less available N from soybean and the soil nutrient complex in the previous year. Sorghum grown in rotation with soybean did not generally respond to fertilizer N, suggesting that high fertilizer N rates are unnecessary in rotation systems. Low September temperatures reduced final yields. Given the high probability of confronting adverse cropping conditions, it is strongly recommended that sorghum be considered as an important component of rainfed cropping systems in eastern Nebraska to ensure minimum crop loss to farmers. Greater economic gains can be achieved by using rotations with soybean because of higher sorghum yields and lower fertilizer costs, and these are most likely under the favorable rainfall and temperature regimes identified in this study. The results provide useful information for fine-tuning management options to maximize sorghum yields and reduce input costs in atypical years.

Evaluation of agronomic and energy traits of Wray sweet sorghum and the N39 × Wray hybrid

Abstract Recent emphasis on energy problems has stimulated efforts to identify crops capable of producing high yields of biomass that can be converted into ethanol. The sorghum [ Sorghum bicolor (L.) Moench] crop includes cultivars and hybrids that vary widely in the relative amounts of grain and stalks produced, and also in the sugar content of the stalks. N39 × Wray, a relatively sweet hybrid with good grain potential, and Wray, a cultivar with sweet stalks, were compared for their grain and sugar yields, alcohol production potential, and other related characters. The hybrid produced heavier seeds, more seeds per head, and more heads per ha than the Wray. This resulted in a grain yield of 6630 kg/ha, about 3.4 times that of Wray. Wray produced about 10% more biomass with the stalk sugars accounting for about 80% of the total alcohol potential as compared to 45% for the hybrid. The total alcohol production potential (stalk plus grain) was 1.11 times as great for the hybrid as for Wray.