The effect of water and nitrogen on the response of sorghum cultivars with contrasting nitrogen use efficiency.

摘要

Water and nitrogen (N) are important environmental factors limiting sorghum production. Information is lacking on the combined effects of water and N for cultivars with different degrees of water and/or N stress tolerance. Sorghum cultivars known for N and water stress tolerance difference were evaluated to identify plant characteristics contributing to N use efficiency (NUE). Cultivars San Chi San and CK-60 were evaluated at Mead, NE on a Sharpsburg silty clay loam soil under water (stress and non-stress), and N (0, 40, 80, and 120 kg ha-1) rates. Experimental units were arranged in split-split plot and treatments were assigned to the whole units using randomized complete block. In the greenhouse, factorial combinations of cultivars, water, and three N rates (10, 20, and 40 mg L-1 N) were evaluated in a randomized complete block. A second greenhouse experiment included the cultivar B-35 in order to further evaluate water (no stress and stress at 8--9 leaf stage) and N (stressed and adequate) responses.; Responses of plant characteristics such as plant height, internode length, flag leaf internode length, flag leaf area, leaf senescence, percent dry matter and N partitioned to nonreproductive plant parts showed a distinct difference between cultivars. Characteristics exhibited by the N-use-efficient cultivar were modified under low N particularly plant height and leaf greenness. These modifications made this cultivar appear undesirable by traditional agronomic standards. Both cultivars had similar performance when neither water nor N was limiting. High N and severe water stress masked NUE of San Chi San plants. Under low N, CK-60 partitioned a greater proportion of DM and N to stems and leaves. This was reversed by increased N application. It is not clear if increased accumulation of DM and N in stems is a drought tolerance attribute or a liability causing N inefficiency. Differences in cultivar preference for NO3 - as a principal N source, and root or shoot as the major site of N reduction is proposed for causing the observed difference in response between the N-use-efficient and inefficient cultivar.