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Isotope-aided Studies on Fertilizer N Recovery and Yield -water Relations of Irrigated Wheat in a Sandy Loam Soil

M. I. Khalil
SoiI Science Division.Bangladesh Institute of Nuclear Agriculture. P. O. Box. 4, Mymensingh-2202. Bangladesh

S. M. Rahman
SoiI Science Division.Bangladesh Institute of Nuclear Agriculture. P. O. Box. 4, Mymensingh-2202. Bangladesh

M. E. Haque
SoiI Science Division.Bangladesh Institute of Nuclear Agriculture. P. O. Box. 4, Mymensingh-2202. Bangladesh

Abstract/ Executive Summary:

Field studies were undertaken to evaluate the yield response and fertilizer N and water use efficiency in irrigated wheat with different fertilizer N rates of 0, 60, 120 and 180 kg N tux as urea. ^l5N enriched urea of 10% u.e. was used only in isotope sup-plots of l -120 and N-180 treatments. The highest yields and water use efficiencies (WUE) were found at the N-180 treatment which did not differ significantly with N-120 in both seasons of 1994-95 and 1995-96. Wheat yield and WUE showed a significant curvilinear relationship with fertilizer N rates. The curvilinear relationship of yields with fertilizer N uptake indicated the limitation of increased N uptake with increased rates of fertilizer N application. ¹⁵N isotopeaided studies showed a higher % Ndff with the increased rates of fertilizer N. Increased amounts of N yielded significantly higher total and fertilizer N uptake, and the %Fertilizer N recovery was comparatively higher in the second year. Wheat utilized fertilizer N for the 40 and 44% from the N-120, and 38 and 41% for the N-180 treatments in the two years respectively. Fertilizer N uptake was positively (R² = 0.98**) and its recovery negatively (R² = 0.71 *) correlated with N rates and showed a linear relationship in both the cases. Split application of the isotope showed a trend of increased N uptake from both the 1 /3rd application during final land preparation and 2/ 3rd application at Zadok's-30. depending on the environment and management conditions. The total fertilizer N loss due to different levels of fertilizer N ranged from 15-18, 44-48 and 76-80 kg ha^-1 in the two years and it increased with the fertilizer N rates. This indicated an adoption of suitable management options to have higher N use efficiency.

Keywords: Fertilizer, Yield water, Wheat, Sandy loam soil

Location: Wheat Research Center, Dinajpur, Bangladesh

Start Date: 00-00-1994

End Date: 00-00-1996

Program Area: Crop-Soil-Water Management

Commodity: Wheat, Land management

Objectives:

To improve N and water use efficiency in cropping system with a view to maintain soil and water resources and to sustain productivity.

Methodology:

The experimental fields were kept fallow during the monsoon period before starting experiment followed by wheat cultivation with uniform irrigation and fertilizaion. It was carried out in a randomized complete block design having 4 replications with a plot size of 8m x 5m (divided longitudinally into two halves for yield and sampling plots). The treatments were: N_o - 0 N (unfertilized check), N₁-60 kg N ha^-1. N₂-120 kg N ha^-1 and N₃-180 kg ha^-1 as urea. There were two isotope sub-plots (1 m x 1 m) in each treatment plot of N₂ and N₃. The first installment (l/3^rd) of the isotope was applied in each subplot at the time of final land preparation. Later on, the remaining 2/3^rd was applied only in one subplot by keeping the other intact but with normal urea. ¹⁵N enriched urea (10% a.e.) was used for both experiment. The other applied fertilizers were 22 kg P, 33 kg K, 20 Kg S, 5 kg Zn and 2 kg B ha! as basal dose including 1/3^rd urea. The remaining 2/3^rd urea was top dressed at Zadok's-30 as practiced by farmers and after disappearance of the irrigation water from the soil surface. Wheat (Triticum aestivumL.cv Kanchan, a widely used variety) seeds were sown on 28 November, 1994 and on 24 November, 1995 during the cropping seasons of 1994-95 and 1995-96 respectively. The first installment of irrigation water was applied at Zadok's- 30 amounting to 7.6 and 3.69 cm for the two growing seasons, respectively, based on the amount of soil water depeted from the 0-45 cm soil zone, up to the maximum water holding capacity, MWHC (18.54 cm of water). The following irrigations were applied to all treatment plots based on the 50% or below depletion of the MWHC from 2 treatment plot. It was 8.47 at anthesis and 3.8 cm after 50% anthesis period during 1994-95 and 1995-96, respectively. The soil water content at 0-15 cm was determined by gravimentry and at 15- 120 cm profile at an intervals of 15 cm using the neutron moisture meter (Troxler, Model-3320). The total amount of rainfall during the growing period was 1.4cm and 2.07cm for the two experimental periods. respectively. The water table depth (WID) was measured at 10 day intervals for both experimental years. The crop was harvested on 5 April in 1995 and on 24 March in 1996. Yields were recorded from a harvested area of 4m x 2m from the middle of the yield plot to avoid border effect, Soil water depletion (SWD) was measured by subtracting the soil water content of the 0-90cm soil profile at owing and harvest, Total water use (1WU) was calculated by adding together the SWD, amount of rainfall and irrigation water, Water use efftciency (WUE) was estimated by dividing the respective grain yield by 1WU. . Plant samples were collected from the centre of the isotope plots as stated. ¹⁵N samples were analyzed at the lAEA's Seibersdorf Laboratories using mass spectrometry. The soil samples were analyzed at the Bangladesh Institute of Nuclear Agriculture (BlNA) using an emission pectrometer. Percent nitrogen derived from fertilizer (%Ndf) , % nitrogen derived from soil (%Ndffs). fertilizer N uptake and utilization or recovery by wheat were computed using ¹⁵N analysis data. The total fertilizer N loss was computed by adding together the fertilizer N recovery by wheat and the residual fertilizer N in the soil and this was subtracted from the rates of added fertilizer N. The predicted values related ¹⁵N parameters for the N I treatment were estimated by regressing the value of total and fertilizer N uptake for N₂ and N₃treatment and the others through back calculation.

Source of Information: Bangladesh J. Soil. Sci. 26: 23 - 31, 2000 (December)

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Increased yields, water use efficiency and fertilizer N recovery by wheat may be obtained with split application of fertilizer . under controlled irrigation. Both 1/ 3^rd application at sowing and 2/3^rd application of fertilizer N under controlled irrigation. both 1/3^rd application at sowing and 2/3^rd application at Zadok's-30 were more or Iess equally effective, depending on the soil and environmental conditions. The total fertilizer N recovery suggested the application of 120 kg N ha^-1, giving attention to other management options for hither recovery. Moreover, the residual fertilizer N in the soil should be brought under consideration in order to avoid considerable loss during the fallow and monsoon cropping season. The heavy and continuous rainfall during monsoons may cause higher leaching losses. Immediate cropping followed by wheat i.e. intensive cropping may be considered to get benefit from the residual N in the soil.

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