Published Date September 2015, Vol.22(5):250–254,doi:10.1016/j.rsci.2015.09.005
Open Access, Creative Commons license, Funding information
Title
Characterization of Nitrogen Uptake Pattern in Malaysian Rice MR219 at Different Growth Stages Using15N Isotope
Author
Mohammad Mu’az Hashim,
Mohd Khanif Yusop
Radziah Othman
Samsuri Abdul Wahid
Department of Land Management, Faculty of Agriculture, University Putra Malaysia, Serdang 43400, Selangor, Malaysia
Received 4 December 2014. Accepted 11 May 2015. Available online 27 September 2015.
Abstract
Nitrogen (N) use efficiency is usually less than 50%, and it remains a major problem in rice cultivation. Controlled release fertilizer (CRF) technology is one of the well-known efforts to overcome this problem. The efficiency of CRF, however, is very much dependent on the timing of nutrient release. This study was conducted to determine the precise time of N uptake by rice as a guideline to develop efficient CRF. Fertilizer N uptake by rice at different growth stages was investigated by using 15N isotopic technique. Rice was planted in pots, with 15N urea as N source at the rate of 120 kg/hm2. Potassium and phosphorus were applied at the same rate of 50 kg/hm2. Standard agronomic practices were employed throughout the growing periods. Rice plants were harvested every two weeks until maturation at the 14th week and analyzed for total N and 15N content. Nitrogen derived from fertilizer was calculated. Total N uptake in plants consistently increased until the 11th week. After that, it started to plateau and finally declined. Moreover, N utilization by rice plants peaked at 50%, which occurred during the 11th week after transplanting. N derived from fertilizer in rice plants were in the range of 18.7% to 40.0% in all plant tissues. The remaining N was derived from soil. Based on this study, N release from CRF should complete by the 11th week after planting to ensure the maximum fertilizer N uptake by rice plants. Efficient CRF should contribute to higher N derived from fertilizer which also resultedin a higher total N uptake by rice plants, increasing the potential of rice to produce higher yield while at the same time of reducing loss.
Keywords
nitrogen use efficiency rice
c
ontrolled release fertilizer
15N isotope
Nitrogen (N) use efficiency (NUE) problem has been widely discussed and studied over the years. In most agricultural crop, the efficiency is low. Use efficiency of fertilizer N in rice is often less than 50% (Katyal et al., 1985andSingh et al., 2001). Inefficient NUE can cause various adverse effects, such as serious environmental problems to the aquatic and terrestrial ecosystem, as well as the atmosphere (Dalton and Brand-Hardy, 2003). Excessive N in the environment can cause respiratory problems, such as ‘bluebaby syndrome’ and cancer from nitrate contamination in drinking water (Galloway and Cowling, 2002).
Fertilizer technology can be a solution for the low N efficiency problem. Controlled release fertilizer (CRF) has the ability to release its nutrient content gradually to coincide with the plant requirement (Hanafi et al., 2000). Plants can remove N in optimum amount by using CRF. CRF will supply the plants with N at the right time and at the right amount. N requirement varies during plant development. Controlled release of N will supply the N accordingly, based on plant development stages (Sharma, 1979).
The time of nutrient release from fertilizer is a crucial element to determine the effectiveness of CRF. Rapid release may cause N loss, while extremely slow release can cause N insufficiency for plant uptake. Thus, predicting N requirement by plant provides important information in designing the release pattern of the CRF.
Isotopic study by using 15N can be used to determine N utilization from fertilizer by plant. Plant can obtain N from various sources, including soil, microbial fixation, and most importantly fertilizer. Fertilizer is applied as 15N isotope to trace the amount of N derived from the fertilizer (NDFF). This information is very essential in developing fertilizer to meet the actual requirement of plant. The advantage of this technique is that the element is traceable. Isotopic 15N is the most common stable isotope used in agriculture-related studies (IAEA, 2001).
MR219 is one of the most common rice varieties commercially cultivated in Malaysia. Its coverage reached a record high of 70.1% in 2002, and the latest recorded coverage was 30%–40% in 2012. Until now, this variety has remained as one of the main varieties applied in Malaysian granary areas. There are several attributes of this particular variety that have made it popular among Malaysian farmers, including short maturation period, long grade grains, low amylose content, high resistance to leaf blight and brown planthopper.
The experiment was conducted to determine the timing of N uptake and NUE by rice during the growing stages.
MATERIALS AND METHODS
Experimental setup and rice establishment
A pot experiment was conducted in a glasshouse. Commonly grown rice variety MR219 was used and the plants were grown in Selangor soil series (Isohyperthermic, Aeric Tropic Fluvaquent) collected from Sungai Besar, Selangor, Malaysia (3°42’20“ N, 100°58’08” E).
Physico-chemical analyses of the soil were conducted. Mechanical analysis of soil was done by pipette method and textural class (clay, 64.0%; silt, 34.5%; sand, 1.3%) was determined using the United State Department of Agriculture soil textural triangle. Soil pH (6.0) was analyzed using Mettler Toledo pH meter in a 1:2.5 ratio of soil to water. Cations exchange capacity (20.2 cmol/kg) was determined using leaching method (Chapman, 1965). Total N (0.15%) was determined using Kjeldahl method with salicylic acid (Bremner and Mulvaney, 1982). Available P (8.54 mg/kg) was determined using Bray No. 2 method (Bray and Kurtz, 1945). Available Cu, Fe, Mn and Zn (0.27, 23.72, 2.70 and 0.30 mg/kg, respectively) were determined using Mehlich No. 1 method (Mehlich, 1953).
Every pot was filled with 10 kg of soil and flooded with water. Water level was maintained at 1–2 cm above the soil surface during the early growth stage and 5–7 cm at the later growth stage. Rice seeds were pre-germinated and grown for 14 d. Rice plants were transplanted into the pots filled with flooded soil at the 15th day. Every pot was planted with four rice plants and each plant was planted separately from one another in the pot.
Fertilizer application and agronomic practice
Recommended rates of 120 kg/hm2 N, 50 kg/hm2 P2O5, and 50 kg/hm2 K2O were applied. N in the form of 15N (urea fertilizer) was applied in three splits on the first day after transplanting (DAT) or basal application, 20 DAT and 35 DAT. Urea labelled with 15N used was ISOTEC™ Urea 15N2, 10% atom excess (a.e). Phosphorus (P) in the form of triple superphosphate and potassium (K) in the form of muriate of potash fertilizer were applied as basal fertilizer. Standard agronomic practices were carried out to control insects, pests, diseases and weeds.
Plant analysis and 15N measurement
Whole rice plants were harvested every two weeks after transplanting, with the final harvest done at 14th week. The harvested plants were dried at 60 °C for 24 h before they were separated into straw, roots and grains.
Total N content in plant tissues was determined using the Kjeldahl method (Bremner and Mulvaney, 1982) and total N uptake was calculated by multiplying total N with dry matter weight. The plant tissues were analyzed for 15N content using an emission spectrometer (IAEA, 2001). Those analyses were conducted at Malaysian Nuclear Agency. The N utilization from the fertilizer was calculated by dividing the percentage of 15N atom excess in the plant with percentage of 15N atom excess in the fertilizer (IAEA, 2001). Both NDFF and N derived from soil (NDFS) in plants were calculated to determine the percentage of N from fertilizer and soil (IAEA, 2001).
NUE (%) = N from 15N fertilizer / Amount of fertilizer applied × 100
Fertilizer N utilization (%) or NUE is calculated by NDFF in plant tissues with the total amount of fertilizer applied (IAEA, 2001). By using this calculation, the percentage of N from the fertilizer that was actually taken up by the plant in relation to the total amount of fertilizer applied can be estimated.
RESULTS
Nitrogen uptake by plant
The total N uptake in plant consistently increased from the first harvest in the 2nd week and reached the maximum in the 11th week (Fig. 1). After the 11th week, total N uptake in plant started to become plateau and eventually decreased.
Fig. 1. Total nitrogen (N) uptake by rice plant at different weeks after transplanting.
The N uptake in rice during the second week was 6.6 g/pot. Then, it started to increase by week and reached its peak during the 10th to 12th weeks at 127.9 g/pot. Towards the end of growing period, total N in rice decreased to 112.3 g/pot during the 12th week and 128.87 g/pot during the 14th week.
Nitrogen use efficiency (NUE)
By implementing standard practice of rice cultivation in which urea was used as the source of N, NUE was only 50.0% (Fig. 2). The highest NUE was achieved towards the end of growing period between the 10th and 14th weeks.
Fig. 2. Nitrogen (N) utilization from fertilizer by rice at different weeks after transplanting.
Source of nitrogen in rice tissues
In general, NDFF is relatively lower than NDFS in all rice plant tissues, straw, grain and root, throughout the growing period. NDFF is in the range of 22% to 40% in straw and 18% to 29% in root while 26% to 28% in grain.
In rice straw, the highest NDFF was 39.9% during the 1st harvest (2nd week after transplanting), and the lowest during the 2nd harvest (4th week after transplanting) was 22.9% (Fig. 3-A). In root, the highest NDFF was recorded during 2nd week after transplanting (29.3%) and the lowest during the 4th week after transplanting (18.7%) (Fig. 3-B), while in rice grain, NDFF was 27.8% during the 12th week and 26.4% during the 14th week after transplanting (Fig. 3-C). In the 4th week after transplanting, NDFF in rice showed the lowest records in both straw and root (Fig. 3).
Fig. 3. Source of nitrogen (N) in rice straw (A), root (B), and grain (C) at different weeks after transplanting.
NDFF, Nitrogen derived from fertilizer; NDFS, Nitrogen derived from soil.
DISCUSSION
Nitrogen uptake by rice plants
During the early stage of growth until the 11th week after transplanting, rice is at the vegetative and reproductive stage (IRRI, 2007). After the 11th week and up to the 14th week after transplanting, rice is at the ripening stage (IRRI, 2007), during which plants undergo grain filling and maturation (De Datta, 1981). During the ripening stage, rice does not absorb N from soil but utilized N that is already available in plant tissues. According to Jones et al (2011), during grain formation and seed filling, large portions of N and P used come from the culm, leaves and panicles, rather than directly from the soil. N from other parts of rice is transferred to the grain for maturation process.
MR219 is a variety that has a short maturation period. This variety can be harvested at 105 to 112 d after planting. For longer maturation period variety, which matures at 130 d after planting, the N uptake may be different because of the differences in the development and growth stage (IRRI, 2007). The information on total N uptake by rice is very useful in developing CRF that meets plant N requirement. Nitrogen should be released from the 1st week until 11th week, during which rice is actively consuming N for vegetative and reproductive growth (De Datta, 1981). If gradual release during this period can be managed, N uptake can be improved compared to the common practice using urea.
While exceedingly fast release is not preferred, the release of N at extremely slow rate also needs to be avoided. The problem of extremely slow release may cause by very thick coating (Trenkel, 2010). If nutrient release is too slow, the plant will not be able to absorb the nutrient when it is needed, especially for annual crops such as rice and maize. For rice, if N from CRF is released too slowly and the release exceeds the period of the 11th week after transplanting, it will not be beneficial because the rice plant ceases to require N from the soil.
Nitrogen use efficiency
NUE is an important indicator in N fertilizer application. Achieving higher NUE always becomes a priority in agriculture. From this study, NUE was only 50%, which meant only 50% of applied fertilizer was consumed by rice plants. The remaining 50% of N from the applied fertilizer was either remained in soil or lost to the environment. This is similar to the results reported by Katyal et al (1985) and Singh et al (2001). Ladha et al (2005) also reported rice NUE at 46%.
NUE in this study was considerably low, and low NUE increases the potential of N loss through several means such as leaching, denitrification and volatilization (Ladha et al., 2005). Low NUE and N loss have been stated as the reasons for various environmental concerns such as groundwater pollution from leaching, eutrophication, and greenhouse gas effects (Ladha et al., 2005).
Increasing NUE can directly reduce the potential of pollution from N fertilizer. Shoji (2005) indicated that increasing NUE from 30% to 80% can reduce potential N fertilizer pollution from 70 kg/hm2 to only 8 kg/hm2. In addition, increasing NUE also increases rice yield. Field experiment of lowland rice showed that an increase in NUE has significant positive effects on rice grain yield (Fageria and Baligar, 2005).
Source of nitrogen in plant tissues
In this study, NDFS was higher in rice plant than NDFF, indicating that the plant absorbed more N that was readily available in soil rather than the N that was being added through fertilizer application. This problem is expected to be solved by using CRF. Nutrient from CRF is released slowly to the soil, allowing efficient removal of N by the plant.
During vegetative period (before 45 DAT) of rice (IRRI, 2007), N is removed by plant very rapidly. By using urea, N is immediately converted into ammonium (NH4). While a fraction of the fertilizer is being removed by plant, the other fraction is lost to the environment, resulting in the low availability of N from fertilizer in soil, increasing the dependency of plant to available N in soil.
A study by Reddy and Patrick (1980) also showed a similar pattern of rice N uptake, that only one-third of N is derived from fertilizer, while the remaining two-thirds of N in plant is derived from soil. A probable cause for the high dependency of plant to NDFS is the rapid depletion of N, especially the applied N from fertilizer (Reddy and Patrick, 1980).
Low NDFF can also result in various adverse effects such as economic loss (Raun and Johnson, 1999) and environmental pollution (Ladha, 2005), as discussed before. From the economic perspective, Raun and Johnson (1999) estimated that global loss from N fertilizer for cereal production is around $15.9 billion annually. This economic loss will automatically increase production cost of agriculture.
CRF is primarily developed to increase NDFF in plant as a result of its ability to supply N to the plant at the right time and amount. Plant can remove N during its various development stages accordingly (Sharma, 1979), allowing the plant to grow better and reduce N deficiency problem. If NDFF can be increased by CRF application, the total N concentration in plant will increase, thus potentially improve the growth and yield of rice.
CONCLUSIONS
Nitrogen uptake by rice plant occurred until the 11th week after transplanting. Fertilizer N utilization by rice only reached up to 50%. NDFF in rice was very low, ranging from 20% to 35%. The findings obtained in this study can be used as a general guideline in developing practical CRF to increase NUE by plant. A good CRF can increase NDFF in plant, thus enabling the plant to absorb higher amount of N for better growth and higher yield.
ACKNOWLEDGEMENTS
Financial support for this study was received from Long-Term Research Grant Scheme of the Ministry of Education, Malaysia under the project ‘OneBAJA: The Next Generation Green and Economical Urea’. Special thanks go to the science officer of Department of Land Management, University Putra Malaysia and the staff of Malaysian Nuclear Agency for their expert works and guidance throughout the study.
International Atomic Energy Agency (IAEA). 2001. Use of Isotope and Radiation Methods in Soil and Water Management and Crop Nutrition: Training Course Series. Vienna: IAEA.
International Rice Research Institute (IRRI). 2007. Rice production course. Available from http://www.knowledgebank.irri.org/erice production/, 14 August, 2015.
Trenkel M E. 2010. Slow- and controlled-release and stabilized fertilizer: An option for enhancing nutrient use efficiency in agriculture. Paris, France: International Fertilizer Industry Association.
