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Browsing by Author "Khosla, Rajiv"

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    Development of Nitrogen rate Recommendations for No-till Dryland Grain Sorghum in Virginia
    Khosla, Rajiv (Virginia Tech, 1998-10-26)
    Little research has been done in the humid mid-Atlantic region to develop full-season N fertilizer recommendations for dryland no-tillage grain sorghum (Sorghum bicolor L. Moench) production. The objectives of this study were: (i) to determine the optimum rate of band-placed starter N fertilizer needed in combination with side-dress N applications to achieve economic grain yields, (ii) to investigate if pre-plant broadcast N applications are as efficient as band-placed plus side-dress N applications, (iii) to evaluate the response of grain sorghum yield to partitioned side-dress N applications, and (iv) to study the influence of residual soil profile mineral-N (nitrate and ammonium) on sorghum response to applied N fertilization. Multi-location field studies were conducted over three years. A range of N treatments of various starter-band and side-dress N rates were applied. The experimental data indicate that an optimum rate of N fertilization depends on residual soil mineral-N. Little or zero starter-band-N in conjunction with side-dress-N applications of 130 kg of N ha-1 for soils testing high in mineral-N ( 50 kg N ha-1 in the top 0.3m of surface soil) at planting, and a starter-band-N supplement of 40 kg N ha-1 in conjunction with 130 kg N ha-1 side-dress N for soils testing low in mineral-N at planting, optimized the grain sorghum yields in these experiments. Broadcast N applications were observed to be as efficient as band placed N applications when followed by rainfall soon after application. Grain sorghum yields did respond to the partitioned side-dress N applications. However, partitioning of side-dress N application again depends on the residual mineral-N level present in the soil. In order to consider residual soil mineral-N in making N fertilizer recommendations "Associated Nitrogen Fertilizer Equivalency" (ANFE) values were calculated. ANFE is the amount of applied N that has potential to produce the same yield as that produced by the residual soil mineral-N. The N fertilizer recommendations based on ANFE values were quite close for two out of four sites as compared to the N rates at which the maximum yields were obtained in this study.
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    Yield and water use efficiency of different plant populations of dryland corn and sorghum
    Khosla, Rajiv (Virginia Tech, 1995-07-31)
    Two field experiments were conducted at the Tidewater Agricultural Research and Extension Center, in Suffolk, Virginia, during summer 1994, on a Uchee loamy sand (fine, loamy, siliceous, thermic Arenic Hapludult) with relatively low water holding capacity. The objective was to determine the effect of plant population on yield, water use, and water use efficiency, of one cultivar of corn (Zea mays L.) and two cultivars of sorghum (Sorghum bicolor (L.) Moench). Plant population treatments for corn were 37, 49, and 62 thousand plants ha⁻¹ of cultivar Pioneer 3140 on a 91- cm inter-row spacing. For sorghum, treatments were factorial combinations of plant populations of 54, 109, 158, and 202 thousand plants ha⁻¹ and cultivars Dekalb-48 and Southern States 1212 on a 46-cm inter-row spacing. Experimental plots were laid out in randomized complete blocks with four replications. Soil water measurements were taken non-destructively at 10-day intervals after planting and at 20-cm intervals to a depth of 1.7 m in the center of each plot, using a Sentry AP-200 moisture probe. Overall mean grain yield for com was 3909 kg ha- l . For sorghum, it was 4800 kg ha-] for cultivar Dekalb-48 and 4740 kg ha⁻¹ for cultivar Southern States-1212. Soil water measurements showed that soil water stress occurred during tasseling of corn at 75 to 83 days after planting. This stress occurred just prior to the boot stage for sorghum at 60 to 68 days after planting. Crop water use, averaged over all treatments, was 494 mm for corn and 424 mm for sorghum. For corn, plant population did not influence grain yield and crop water use. Water use efficiency ranged from 0.748 to 0.873 kg m³. For sorghun1, there was no interaction between plant population and cultivar. Grain and dry matter yield, crop water use, and water use efficiency were similar for both the cultivars. Significant plant population effects were obtained for both sorghum cultivars. Grain and dry matter yield were depressed at the lowest plant population. Water use efficiency for sorghum increased non-linearly with increase in plant population from 0.944 to 1.354 kg m³.