dry matter partitioning, growth analysis and water use efficiency response of oats (avena sativa l.) to excessive nitrogen and phosphorus application

shoot:root ratio, dry matter partitioning, growth analysis, and water use efficiency of oat (avena sativa l., cv. walker) was investigated under excessive nitrogen (n) as 200 mg n kg-1 (n1p0), excessive phosphorus as 200 mg p kg-1 (n0p1), and combined 100 mg n+100 mg p kg-1 (n2p2), and the control (n0p0) as check in a pot experiment at dryland agriculture institute, west texas a and m university, canyon, texas, usa, during winter 2009-2010. the experiment was performed in completely randomized design (crd) with three replicates. one week after emergence, 15 plantswere maintained per pot. later, five plants were uprooted at 30, 60, and 90 days after emergence (dae). the volume of each pot was 6,283 cm3, containing 2,000 g of potting mix (organic soil) pot-1. excessive n applications had very negative effects on leaf, stem, and root and, consequently, on the total dry weight per plant of oat. the reduction in total plant dry weight with excessive n applications reduced crop growth rate. in contrast, excessive p applications had no negative effects on leaf, stem, root, and the total plant dry weight. rather, excessive p applications had more favorable effects on leaf, stem, root, and total dry weight per plant at early growth stage. at later growth stages, combined n+p applied had more beneficial impact on leaf, stem, root and total dry weight per plant. the increase in total dry matter accumulation per plant showed positive relationship with absolute growth rate (agr), crop growth rate (cgr), and net assimilation rate (nar). the nar showed negative relationship with increase in lai and positive relationship with increase in cgr. water use efficiency was increased with p application and showed positive relationship with increase in cgr.