Specific Leaf Area and Specific Leaf Weight in Small Grain Crops Wheat, Rye, Barley, and Oats Differ at Various Growth Stages and NPK Source

Leaf thickness plays an important role in leaf and plant functioning and is related to species' strategies of resource acquisition and use. Leaf thickness in small grains crops was measured as specific leaf area (SLA) (leaf area in cm(2) produced g(-1) leaf dry weight plant(-1)) and specific leaf weight (SLW) (leaf dry weight in mg produced cm(-2) leaf area plant(-1)). The four small grains crops (cool season C-3 cereals) studied were wheat (Triticum aestivum L.), rye (Secale cereale L.), barley (Hordeum vulgare L.) and oats (Avena sativa L.). The null hypothesis tested was that SLA and SLW in small grain crops do not differ at different growth stages and nitrogen, phosphorus, and potassium (NPK) source. Eight NPK sources used in the experiment were: S-1 = 20-20-20, S-2 = 20-27-5, S-3 = 7-22-8, S-4 = 10-10-10-20S, S-5 = 11-15-11, S-6 = 31-11-11, S-7 = 24-8-16, and S-8 = 19-6-12, and each was applied at the rate of 300mg pot(-1) at the time of sowing to each crop species. The experiment was performed in completely randomized design with three repeats at the Green House of Dryland Agriculture Institute, West Texas A&M University, Texas, during winter 2009-10. Based on the results, it was observed that both SLA and SLW differed with change in crop species, growth stage and NPK source. Among the crop species, SLA was greater in oats > barley > rye > wheat at different growth stages; while SLW of wheat and rye > barley and oats. The differences in the SLW between wheat vs. rye; and between oats vs. barley at different growth stages were not significant (P <= 0.05). Among the NPK sources, application of S-7 (24: 8: 16) had higher SLA at 60 and 90 DAE (days after emergence). Application of S-6 (31: 11: 11) had higher SLW at 60 DAE due to the production of the lowest leaf area plant(-1), but the increase in SLW at 90 DAE with S-5 and S-4 was due to the higher leaf dry weight plant(-1)produced. Leaf dry weight and leaf area plant(-1) were considered the two most important leaf characteristics that influenced SLA and SLW. On the average, SLA increased with passage of time i.e. 0.70 < 520 < 600cm(2) g(-1) at 30, 60 and 90 DAE, respectively; but SLW on the other hand, was highest 3.5 at 60 DAE > 2.2 at 90 DAE > 1.5mg cm(-2) at 30 DAE. The increase in leaf area plant(-1) and decline in the leaf dry weight plant(-1) increased SLA; in contrast, increase in leaf dry weight plant(-1) and reduction in leaf area plant(-1) increased SLW indicated reciprocal relationship between SLA and SLW in the crop species.