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Temporal Origin of Nitrogen in the Grain of Tropical Wet-Season Rice

^a IRRI, DAPO 7777, Metro Manila, Philippines
^b Dep. of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE 68583
^c Dep. of Animal and Plant Sciences, Univ. of Sheffield, Sheffield S10 2TN, UK
^d Dep. of Agronomy, Univ. of the Philippines, Los Baños, Philippines

View larger version (18K): [in a new window]   Fig. 1. (a) Time course for recovery of 15N in rice plants from an application of labeled (99% atom 15N excess) nitrate at () 17 DAT and () 55 DAT at the 5-cm soil depth in the wet season of 2001. Each point is the mean of four replicates and vertical lines indicate standard errors. The curve for 17 DAT is Rc = 0.26[1 – exp(–1.01tdal)], r2 = 0.95 and for 55 DAT is Rc = 0.22[1 – exp (–0.28tdal)], r2 = 0.96. (b) The recovery of 15N in rice plants at weekly intervals following an application of labeled (99% atom 15N excess) () nitrate and () urea at 35 DAT, at the 5-cm soil depth in the wet season of 2001. Each point is the mean of four replicates and vertical lines indicate standard errors. The curve for nitrate is Rc = 0.23[1 – exp(–0.27tdal)], r2 = 0.95 and for urea is Rc = 0.58[1 – exp(–0.47tdal)], r2 = 0.80.

View larger version (18K): [in a new window]   Fig. 2. (a) The accumulation of total N (g hill–1) by (•) rice plants or () the panicles in an irrigated crop during the wet season, represented by sigmoid curves. The equations were Nc = 0.96/[1+(t/37.83)–2.66] for the rice plants and Nc = 0.37/[1+(t/75.89)–13.91] for the panicles. The points represent measurements of total net N content of the plants with standard errors (n = 4). (b) Rate of total N uptake by the (solid line) whole plants or the (dashed line) panicles. These curves are the first differential of Eq. [5], with parameters given in the legend to Fig. 2a.

View larger version (28K): [in a new window]   Fig. 3. The distribution of 15N (applied on 17, 31, 45, 59, and 73 DAT) to different plant parts () 14 d after application and the reallocation of that N (none is lost from the plant) () at maturity. Standard errors are shown (n = 8) and each point is calculated independently of the others on any given day.