Drought Reponses and Nitrogen Partitioning in Maize Genotypes under Different Soil Moisture Regimes¹

 

Somchai Boonpradub

Phitsanulok Field Crops Experiment Station. Wangthong,  Phitsanulok, Thailand.

 

 

1. Ph.D. dissertation, Chiang Mai University.

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Abstract

Maize productivity is often limited by drought stress particularly in rice-based cropping systems.  Three field experiments were conducted on a Typic Plithaqults soil at the farm of Phitsanulok Field Crops Experiment Station from November 1997 to April 1999.  Experiment 1, thirty-one maize genotypes were evaluated and compared for relative degree of drought tolerance imposed at 2 weeks after emergence using a line source sprinkler irrigation system.  Among the thirty-one genotypes, Cargill 7140, Cargill 919, Cargill 717, G 5431, and SW 3601 were the most drought tolerance and were suited for the drought prone area, while genotypes DK 888, NSX 9607, NSX 9210, and G 5445 were moderately drought tolerance and were suitable for the partial irrigated area.  Pacific 700, Pioneer 3012, Cargill 7122, Cargill 727, Pioneer 3013, Pacific 300, Cargill 7118, G 5449, and NS 1 were identified as drought susceptible genotypes which performed well under irrigation treatment.

                Experiment 2, three maize genotypes were selected to determine the differences in morphological and physiological responses to drought under difference soil moisture regimes.  Results showed that water stress reduced total dry matter, kernel yield, crop growth rate, stalk growth rate, leaf growth rate, kernel growth rate, leaf area index, and leaf area duration of all three maize genotypes in both years (1998-1999).  However, specific leaf weight increased with increasing drought stress.  Water stress promoted leaf senescence and reduced effective leaf area and caused low dry matter production in all genotypes.  Among the three genotypes, SW 3601 had higher yield, had lower canopy temperature, had low leaf senescence and resisted greater water stress than NSX 9210 and NS 1.  This result was probably associated with a higher crop growth rate, higher partitioning coefficient, higher root density and extracted greater amount of water from deeper soil profile of the SW 3601 genotype.  Lack of water in the dry regime reduced kernel yield of NS 1, NSX 9210, and SW 3601 genotypes by an average of 49, 45 and 35%, respectively.  Among the yield components, kernel number and kernel weight were the most sensitive to drought followed by ear number.

                Experiment 3, three maize genotypes were used to evaluate nitrogen partitioning under different nitrogen levels and soil moisture regimes.  Water stress and nitrogen deficit affected productive development and source-sink relationship.  Leaf, leaf sheath and stalk including tassel acted as a major sink for nitrogen during vegetative growth stage and then became as a source during kernel development.  However, greater remobilization of reduced nitrogen compared to assimilation in both nitrogen levels was from stalk at the early kernel filling stage.  While remobilization from stalk at low nitrogen fertility was rapidly decreased when severe drought occurred at the final stage of kernel development.  Husks, silk and cob initially served as a sink for nitrogen and then became as a source during the reproductive phase.  Increasing the accumulation of kernel dry weight and nitrogen during kernel development stage may be associated with the remobilization of nitrogen from vegetative and from the other reproductive tissues.  Kernel yield of all genotypes was also affected by water and nitrogen deficits.  Nitrogen supply had a large effect on kernel yield by altering kernel number and kernel weight.  Among the three genotypes, SW 3601 genotype showed the most drought tolerance under low and high nitrogen supplied due to the least value of DSI (39%) and the greater value (1.14) of DI, followed by NSX 9210 and NS 1 genotypes.  SW 3601 also had the highest percentage of total dry weight and total nitrogen content in kernel in both low and high nitrogen levels, and also produced the highest dry matter and nitrogen partitioning from vegetative tissues to kernels as compared to NSX 9210 and NS 1 genotypes.  Thus, SW 3601 genotype could perform well in drought prone area as well as in the partially irrigated land and also appears to be the best genotype to be grown both in the low and high nitrogen fertility areas.

                Experiment 4, three maize genotypes were used to estimate the genetic coefficients for validation of the CERES-Maize model.  It was indicated that the CERES-Maize model could illustrated satisfactory simulation of the phenological events particularly at silking and maturity dates.  However, the simulation of crop growth, kernel yield and kernel number did not conform to the model.  Results illustrated that the model was capable of simulating phenological events but over-estimates for crop growth and kernel yield.  Results also confirmed that the large discrepency between simulated and observed was associated with the yield loss that caused by bird, rat, insect, disease, and harvesting.  The CERES-Maize model could help maize grower for crop management schedule in terms of the timing for fertilizer application, pesticide, irrigation, and harvesting time.  This also could help maize grower to predict the potential yield at a particular area.