Sign up for email alerts of new Fluid Journal issues!
Fluid Journal : Fluid Journal 1996-1998
1 Fluid Journal Fall 1998 Summary: Three years (1995-1997) of research work with fertilizer management on grain sorghum production in Coastal Virginia has demonstrated that it would be unwise to ignore residual soil mineral-N present in the profile at planting. Increased frequency of drought in Virginia over the last two decades, coupled with changes in crop production systems from conventional- till to reduced-till to no-till, suggests the possibility of residual N accumulations. Both drought years (1995 and 1997) showed agronomically significant levels of soil mineral-N, ranging from 67 lbs/A to 134 lbs/A of N at grain sorghum planting time. During these two years, grain sorghum had no significant response to N fertilizer application. Sufficient levels of mineral-N already existed in the soil profile and lack of moisture limited grain yields. Grain sorghum is a relatively new crop in Virginia. Being more drought tolerant, it is an acceptable alternative to corn whose yields have been reduced by frequent droughts during the last 15 years in Virginia. Sorghum is grown on about 15,000 to 25,000 acres, mostly under no-till conditions for erosion control and more efficient use of available water. However, acreage has not increased over the years because adequate production practices to increase yields on no-till systems have been lacking. Growers also have not had access to adequate, equitable markets for grain sorghum, which are now available. Efficient fertilizer management, especially N, continues to be a challenge in high-residue (no-till) farming systems, especially on sandy soils having low organic matter. No-till systems often produce lower yields because of N availability, slower mineralization, greater immobilization, denitrification, and volatilization. This complexity with N management suggests that more research is needed if we are to achieve more efficient management of N fertilizer. Since data are lacking, research is also needed to determine if phosphorus and sulfur applications on soils testing high in phosphorus, and on soils with variable sulfur levels, will produce more vigorous stands that result in higher grain yields. Our objectives in these studies were to: • measure rate of banded N starters needed to optimize sorghum yields in combination with sidedress N • determine if preplant broadcast N is as efficient as banded plus sidedressed N • measure grain sorghum yield response to banded phosphorus • measure yield response to broadcast sulfur at planting. The data in this report are from our 1997 findings, the last year of our study. Climate Field observations during the growing season revealed signs of water R. Khosla, Dr. M.M., Alley, P.H. Davis, Dr. D.E. Brann High Residual Soil Mineral-N Impedes Response Virginia researchers find increased residual N accumulations in soil from drought and changing crop practices can sharply reduce crop response to additional N applications. stress. Visual symptoms (rolling of leaves, adventitious roots at the basal node of plants) were evident at both locations, even during the vegetative growth stage. Soil mineral-N An NPS analysis of profile soil samples taken at the Henrico site at planting is shown in Figure 1. Data from the New Kent site were similar. Though surface organic matter content was less than 2 percent at the Henrico site, note that the soil had significant amounts of soil profile mineral-N. These residual mineral-N levels reflect the nitrogen that probably mineralized from the previous soybean crop. The amounts in the deeper horizons could only have come from previous nitrogen applications. These agronomically significant levels of soil profile mineral- N of 100 lbs/A warrant consideration in developing more efficient N fertilizer recommendations for grain sorghum production on the sandy soils of Virginia. Objectives 1 and 2 There was no significant yield response to N fertilization treatments banded at either location. This lack of response is reasonable in light of substantial residual mineral-N levels present at the time of planting, coupled with lack of moisture during the growing season. Leaching losses during the growing season would also be expected to be insignificant because of low rainfall and high evapotranspiration due to high temperatures. Residual mineral nitrogen levels were
Fluid Journal 1993-1995
Fluid Journal 1999-2001