For several years, rapid tisue tests have ben used in the field to evaluate plant nutritional status and to diagnose deficiencies. But they have ben used only incidentaly to make fertilizer recomendations, or to evaluate a fertilizer program, partly because they have lacked the acuracy of laboratory analysis. Research has revealed definite and consistent relationships betwen plant nutrient level and plant health. However, few crops are routinely tested to determine plant nutritional neds, because fertilizer has ben plentiful and relatively low in cost, and because results from laboratory analyses are often delayed. Rapid tisue tests conducted in the field could overcome the problem of delay. By providing information about nutrients neded for a particular crop in any given field, the tests also enable growers to more fuly utilize increasingly costly and limited fertilizer resources. In the field investigations reported here, a rapid tisue testing procedure (developed by R. H. Bray in 1945 at the University of Ilinois) was found useful as a guide for evaluation of the nitrogen nutritional status of corn and sorghum. Resulting guidelines are given here for recomending aplication rates for nitrogen fertilization and for evaluation at the end of the growing season.

The duration of the residual effects of crop rotations on the fertility and physical condition of montmorillonitic clay soil is not well established. The purpose of this study was to evaluate the residual effects of three crop rotations on water intake, soil loss, soil organic matter, and crop yield during five growing seasons of continuous grain sorghum (Sorghum bicolor (L.) Moench) grown on Houston Black clay soil. Water intake and soil loss were evaluated in the laboratory by the application of water drops at the rate of 10.2 cm/hour from a height of 1 m to the surface of undisturbed soil cores. Oats (Avena sativa L.)-grain sorghum and fescuegrass (Festuca arundinacea Schreb.)-grain sorghum rotations significantly (5% level) increased water intake and reduced soil loss for 20 months after the rotations were discontinued. The sweetclover (Melilotus alba Desr.)-grain sorghum rotation had no effect on soil loss but had a significant (5% level) residual effect on water intake for 8 months after rotations were discontinued. Grain sorghum rotations with either fescuegrass or sweetclover caused significantly more (5% level) water stable aggregates. However, one growing season of grain sorghum following sweetclover reduced aggregation to near that of soil in continuous grain sorghum. There was no significant change in aggregation in fescuegrass rotation plots after 20 months. Most of the organic matter accumulated in 10 growing seasons of a sweetclover-grain sorghum rotation was lost after 5 growing seasons of continuous grain sorghum. Soil organic matter in former grain sorghum rotations with fescuegrass or oats showed nonsignificant change after 5 years of continuous forage sorghum. Grain sorghum yield was significantly greater (5% level) for four growing seasons on the former sweetclover-grain sorghum plots than on the continuous grain sorghum plots. Nitrogen fertilizer had a significant (5% level) residual effect on continuous grain sorghum yield for 2 years. The residual effects of previous crop rotations can significantly affect (5% level) water intake and soil loss for 20 months and crop yield for 1 to 4 years after rotations are discontinued. Growing sorghum continuously for 5 years reduced water intake significantly and caused a continuous slow decrease in soil organic matter.

A sorghum (Sorghum bicolor L. Moench.) canopy has been described as a wick; hence, its evapotranspiration would depend to a large extent on its energy supply. The objective of this study was to determine the effect of row spacing on the energy balance of sorghum. Measurements were made on wide (0.92 m) and narrow (0.46 m) spaced rows of sorghum with equal linear plant density (12 plants/m). Evapotranspiration (lysimeter), net radiation, and soil heat flux were measured. Sensible heat flux was obtained as a residual in the energy balance. Seasonal evapotranspiration was about 10% more from wide row than from narrow row sorghum. High rates of evapotranspiration were maintained on wide row sorghum by row advection during the first part of the growing season and largemale advection during the latter part of the growing season. This study suggests that sensible heat and, consequently, evapotranspiration can be reduced by narrow row spacing in sorghum.

Influence of Mn nutrition on sorghum [Sorghum bicolor (L.) Moench.] was investigated to determine the effects of Mn on early growth and define Mn deficiency symptoms under controlled conditions of nutrient solution culture in the greenhouse. Sorghum plants were grown in the greenhouse in nutrient solution containing eight Mn levels from O to 4,000 μg Mn/liter with all other essential nutrients supplied at adequate levels. Growth retardation determined from plant height measurements resulted prior to the development of visible Mn deficiency symptoms. In addition to the usual Mn deficiency symptoms of interveinal chlorosis, symptoms on sorghum Dekalb ‘BR 64’ included brown-reddish pigmented bands in interveinal areas following chlorosis. Under slight Mn stress conditions, Mn deficiency symptoms decreased hi severity from young to older leaves.

Little information is available on the characteristics of plant roots that determine their effectiveness in nitrate uptake. The effectiveness of nitrate uptake of corn (Zea mays L.), soybeans (Glycine max L.), sorghum (Sorghum bicolor L.), and bromegrass (Bromus inermus L.) intact roots were investigated in nutrient solution culture. The maximum uptake rate per centimeter of root for corn occurred at 10 mM, for sorghum at 2.4 mM, and for bromegrass at 0.8 mM. Increasing the nitrate level above 1.0 mM did not increase the growth rate during the first 3 weeks for any of these species. The minimum level to which the plant roots reduced the nitrate concentration was 1.7, 2.7, 2.4, and 1.4 µM for forage sorghum, grain sorghum, soybeans, and bromegrass, respectively. Three cultivars of corn were compared. Two reduced the nitrate level to 2 µM and the third to 4 µM. The results of this research indicate that the roots of the species investigated absorbed nitrate of maximum rates from relatively low nitrate concentrations provided the concentration was maintained. Also, the degree of reduction in nitrate level where nitrate in solution was not maintained indicated that these plant roots had the absorptive capacity to reduce solution nitrate to concentrations of 4 µM or less.

THE OPTIMUM PLANTING time for wheat and barley in Imperial Valley is between December 15th and January 15th, which makes them excellent crops to follow cotton and late-plantings of grain sorghum. The growing period (and production) of the cereal crops might be increased if the time between the harvest of cotton or grain sorghum and the planting of wheat and barley could be shortened, by eliminating some irrigation and tillage operations. These possibilities were investigated during an experiment designed to compare wheat (Siete Serros and Anza) and barley (CM 67) in the winters of 1971-72 and 1972-73 under maximum and minimum soil preparation following cotton and grain sorghum.