Determination of critical nitrogen dilution curve based on stem dry matter in rice

Abstract

Plant analysis is a very promising diagnostic tool for assessment of crop nitrogen (N) requirements in perspectives of cost effective and environment friendly agriculture. Diagnosing N nutritional status of rice crop through plant analysis will give insights into optimizing N requirements of future crops. The present study was aimed to develop a new methodology for determining the critical nitrogen (Nc) dilution curve based on stem dry matter (SDM) and to assess its suitability to estimate the level of N nutrition for rice (Oryza sativa L.) in east China. Three field experiments with varied N rates (0-360 kg N ha(-1)) using three Japonica rice hybrids, Lingxiangyou-18, Wuxiangjing-14 and Wuyunjing were conducted in Jiangsu province of east China. SDM and stem N concentration (SNC) were determined during vegetative stage for growth analysis. A Nc dilution curve based on SDM was described by the equation (Nc = 2.17W(-0.27) with W being SDM in t ha(-1)), when SDM ranged from 0.88 to 7.94 t ha(-1). However, for SDM < 0.88 t ha(-1), the constant critical value Nc = 1.76% SDM was applied. The curve was dually validated for N-limiting and non-N-limiting growth conditions. The N nutrition index (NNI) and accumulated N deficit (Nand) of stem ranged from 0.57 to 1.06 and 51.1 to -7.07 kg N ha(-1), respectively, during key growth stages under varied N rates in 2010 and 2011. The values of ΔN derived from either NNI or Nand could be used as references for N dressing management during rice growth. Our results demonstrated that the present curve well differentiated the conditions of limiting and non-limiting N nutrition in rice crop. The SDM based Nc dilution curve can be adopted as an alternate and novel approach for evaluating plant N status to support N fertilization decision during the vegetative growth of Japonica rice in east China.

Figure 1. Changes of stem nitrogen concentration (% S_DM) with time (days after transplantation) for rice under different N rates in experiments conducted during 2010 and 2011.

Figure 2. Critical nitrogen data points and N_c dilution curves in stem obtained by non-linear fitting for two rice cultivars (LXY-18, N_c = 2.33W^−0.29 and WXJ-14, N_c = 2.08W^−0.29) under different N rates in experiments conducted during 2010 and 2011.

Figure 3. Critical nitrogen data points used to define the N_c dilution curve when data were pooled over for two rice cultivars (LXY-18 and WXJ-14).

The solid line represents the N_c dilution curve (N_c = 2.17W^−0.27; R² = 0.84) describing the relationship between the N_c and stem dry matter of rice. The dotted lines represent the confidence band (P = 0.95).

Figure 4. Comprehensive validation of N_c dilution curve using independent data set from experiment conducted in 2007.

Data points (◊) represent N limiting growth conditions, while (□) represent N non-limiting conditions. The solid line in the middle represents the N_c curve (N_c = 2.17W^−0.27) describing the relationship between the N_c and stem dry matter of rice. The data points (Δ) and (○) not engaged for establishing the parameters of allometric function (2010 and 2011) were used to develop two boundary curves, (–•–•–•) minimum limit curve (N_min = 1.19 W^−0.31) and (------) maximum limit curve (N_max = 2.27W^−0.25).

Figure 5. Changes of nitrogen nutrition index (NNI) with time (days after transplantation) for rice stem under different N rates in experiments conducted during 2010 and 2011.

Figure 6. Changes of accumulated N deficit (N_and) with time (days after transplantation) for rice stem under different N rates in experiments conducted during 2010 and 2011.

Figure 7. Relationship between changes of nitrogen nutrition index (ΔNNI) and changes of nitrogen application rates (ΔN, kg N ha⁻¹) at different growth stages in experiments conducted during 2010 and 2011.

The open symbols represent different growth stages for LXY-18 while filled symbols represent different growth stages for WXJ-14. (ΔN = A×ΔNNI+B; A = −16.60×DAT+2101, R² = 0.95; B = −0.024×DAT²+2.57×DAT−40.07, R² = 0.62).

Figure 8. Relationship between changes of accumulated N deficit (ΔN_and) and changes of nitrogen application rates (ΔN, kg N ha⁻¹) at different growth stages in experiments conducted during 2010 and 2011.

The open symbols represent different growth stages for LXY-18 while filled symbols represent different growth stages for WXJ-14 (ΔN = C×ΔN_and+D; C = 18.97 ln(DAT)-89.22, R² = 0.98 and D = −9.98 ln(DAT)+52.76, R² = 0.19), respectively.

Figure 9. Comparison of different N_c dilution curves.

The (------) represents the N_c dilution curve of Sheehy et al. (1998) (N_c = 5.20W^−0.50) on plant dry matter basis in Indica rice under tropic environment. The (–•–•–•) represents the N_c dilution curve of Ata-Ul-Karim et al. (2013) (N_c = 3.53W^−0.28) on plant dry matter basis in Japonica rice in Yangtze River Reaches. The (——) line represents N_c dilution curve of Yao et al. (2014) (N_c = 3.76W^−0.22) on leaf dry matter basis in Japonica rice in Yangtze River Reaches, and the (–••–••–) line represents N_c dilution curve on stem dry matter basis in present study (N_c = 2.17W^−0.27).