Nitrogen Use Efficiency of Staygreen Sorghum Under Three Soil Water levels

1. Nitrogen Use Efficiency of Staygreen Sorghum Under Three Soil Water levels Sylvester Addy *, M.R. Reddy and Carl Niedziela North Carolina A&T State University, Abstract The soil used was Enon sandy loam. The pots (25cm diameter) were filled with 10 kg of soil. Seeds of sorghum variety (BTx642) were planted in march and grown to grain filling stage. N fertilizer rates of (67, 100 and 134 kgha-1) were applied at 3, 6 and 9 weeks after planting. Three soil water treatments of 0.3, 0.8 and 1.8 bars were applied from anthesis until harvesting. Data were collected for leaf fresh weight, dry weights of Ieaf, stover, root, grain and leaf water content. Leaf Area Index (LAI) and SPAD Chlorophyll readings were taken on the second leaf from the flag leaf before anthesis till harvest. NUE was calculated as the ratio of grain weight to N applied. Nitrogen use efficiency (NUE) for cereal production worldwide is approximately 33% with the remaining 67% representing a $15.9 billion annual loss of Nitrogen (N) fertilizer. Many parts of the world are becoming more arid due to climate change. In this light, methods that increase NUE and water use efficiency farmer profitability are no longer simply commendable, but required. Breeding programs have identified certain adaptations that present great promise for the development of crops that are tolerant to low levels of  N and soil water. The Staygreen character of sorghum is a unique example of these adaptations. A greenhouse study was conducted at NCA&T State University to determine the nitrogen use efficiency of staygreen sorghum variety (BTx642) at 67, 100, 134 kgha-1and soil moisture levels of field capacity(0.3 bars), half-field (0.8 bars) and one-third field (1.8 bars) capacities. Moisture levels significantly (P=0.05) decreased NUE by 45% and 41% at 1.8 bars and 0.8 bars respectively. Grain weight was also significantly (P=0.05) reduced by 20% at both 1.8 and 0.8 bars. However, NUE was similar under different rates of N. Leaf fresh weight, dry weights of Leaf, stover, root and leaf water content were not significantly affected by N and soil moisture levels. Results and Discussion Figure 4. Effects of N and water levels on NUE There was no significant interaction observed between N and water stress levels. Water stress significantly (P=0.05) decreased NUE by 45% and 41% at 0.8 and 1.8 bars respectively. This agrees with the report of Eghball and Maranville (1991) that NUE generally parallels water use efficiency (WUE) in corn. Single factors N and water did not significantly reduce leaf fresh weight, dry weights of Ieaf, stover, root, leaf water content, LAI and SPAD Chlorophyll readings. Grain weight was also significantly (P=0.05) reduced by 20% at both 0.8 and 1.8 bars. Chlorophyll readings did not significantly differ for the three N levels during post anthesis period. Plants maintained similar chlorophyll level throughout the grain filling period even under limiting water supply. Borrell et al., (2000) reported this phenomenon and explained that as early as 40 days after emergence, more N is allocated to the leaves of staygreen hybrids compared with their senescent counterparts, resulting in a higher specific leaf nitrogen. Introduction Nitrogen Use Efficiencycomprises recovery of fertilizer N, either in grain or in total above ground biomass in the current crop, and a part of the applied N that is immobilized in the soil (Ladha et al., 2005). N fertilization has been a powerful tool in increasing grain yield especially for cereals such as sorghum. Concerns on groundwater quality, public health and rising energy costs have moved economic concerns to the forefront. Farmers must therefore optimize the application of N fertilizers to minimize and avoid pollution by nitrates and to preserve their economic margin while producing economic yields. Sorghum [Sorghum bicolor (L) Moench] hybrids containing the stay-green trait retain more photosynthetically active leaves under drought than do hybrids that do not contain the trait. Yield increases in stay-green types have been attributed directly to maintenance of photosynthetic capability during the grain filling period. NUE has been studied for rice (Singh et al., 1998; Ladha et al., 1998), wheat (Ortiz. et al., 1997), and maize (Hirel et al., 2001).However, information is limited on sorghum. Conclusion Water stress below 1.8 bars decreased the NUE and grain yield of staygreen sorghum BTx642. This genotype however maintained similar physiological characteristics under the three water stress levels. It is important to use N efficient sorghum cultivars to produce sustainable yields and reduce environmental contamination. References Objective Borrell, A.K., and G.L, Hammer. 2000. Nitrogen Dynamics and the Physiological Basis of Stay-Green in Sorghum Crop Sci. 40: 1295- 1307. Eghball, Bahman, and J.W. Maranville. 1991. Interactive effects of water and nitrogen stresses on nitrogen utilization efficiency, leaf water status and yield of corn genotypes. Commun. Soil Sci. Plant Anal. 22:1367-1382. Ladha J. K., G. J. D. Kirk, J. Bennett, S. Peng, C. K. Reddy, P. M. Reddy, U. Singh (1998). Opportunities for increased nitrogen use efficiency from improved lowland rice germplasm. Field Crops Research 56, 41-71. Ladha, Pathak, Krupnik, Six, and van Kessel. Efficiency of Fertilizer Nitrogen in Cereal Production: Retrospects and Prospects 2005 Advances in Agronomy.Volume 87. Ortiz-Monasterio J. I. R., K. D. Sayre, S. Rajaram, and M. McMahon (1997). Genetic progress in wheat yield and itrogenuse efficiency under four nitrogen rates. Crop Science 37898-904. Singh U., J. K. Ladha, E. G. Castillo, G. Punzalan, A. Tirol- Padre, M. Duqueza (1998). Genotypic variation in nitrogen use efficiency in medium and long duration rice. Field Crops Research 58, 35-53. To evaluate the NUE and physiological characteristics of staygreen sorghum under different soil water treatments. Figure 2. Relationship of soil water levels on growth and yield of staygreen sorghum Materials and Methods The experimental design was a 3 x 3 factorial in a randomized complete block with four replications. Figure 3. Chlorophyll meter readings under N rates during post-anthesis. Figure 1. sorghum study in the greenhouse