Influence of levels and time of nitrogen application on yield, nutrient uptake and post harvest nitrogen status of soil in aerobic rice

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1 Influence of levels and time of nitrogen application on yield, nutrient uptake and post harvest nitrogen status of soil in aerobic rice M. Ganga Devi*, V. Sumathi, S. Tirumala Reddy and P. Aruna Department of Agronomy, S.V. Agricultural College, Tirupati , Andhra Pradesh, India * devimadu@gmail.com Food security in Asia depends on irrigated rice eco system. Rice consumes about 90% of the fresh water resources in Asia used for agriculture. However, the increasing scarcity of fresh water threatens the sustainability of the irrigated rice ecosystem (Tuong and Bouman, 2003). In aerobic conditions, growing high yielding rice in non-puddled and nonflooded aerobic soil with the support of external inputs like supplementary irrigation and fertilizers were studied (Bouman et al., 2002). Aerobic culture was tested for different varieties of rice but to test the feasibility of the scented variety of rice under aerobic culture the present study was undertaken. Shobha Rani et al. (2002) focussed that Vasumati scented variety is more suitable for Andhra Pradesh, since it possesses distinct qualities and insulated with pest and disease resistance and thereby making it pesticide residue free for export. Considering growers perspective as well as export orientation, cultivation of scented rice seems to be better option. Nitrogen is the major nutrient that most frequently limits the rice production and is the key input in nutrient management and nitrogen use efficiency that would be in the range of 40 to 60 per cent in low land paddy cultivation. As aerobic rice culture is a new system, there is urgent need to develop suitable management schedule of nitrogen for scented rice. Application of nitrogen at right time is perhaps the simplest agronomic solution for improving the use efficiency of nitrogen. Hence, the present study was conducted to study the response of scented rice to different levels of nitrogen and time of application in aerobic conditions. A field experiment was conducted during rabi, 2007 in dry land farm of S.V. Agricultural College, Tirupati. The soil of the experimental site was sandy clay loam in texture, neutral in reaction, non-saline, low in organic carbon and the initial nutrient status was 202, 21.4 and 205 N- P 2 O 5 -K 2 O kg ha -1, respectively. The variety taken for study was vasumati a scented rice variety. The experiment was laid out in a randomized block design with factorial concept and replicated thrice. The treatments comprised of four levels of nitrogen as factor-i i.e.100, 125,150 and 175 kg N ha -1 and four levels of time of application of nitrogen as factor-ii i.e. T 1 ½ basal + ¼ at active tillering and ¼ at panicle initiation, T 2-1 / 3 basal 1 / 3 + at active tillering and 1 / 3 at panicle initiation, T 3 ¼ basal + ¼ at active tillering + ¼ at panicle initiation and ¼ at heading, T 4 ¼ basal + ¼ at active tillering + ¼ at panicle initiation and ¼ at flowering. Entire dose of phosphorus and potassium were applied basally as per the recommended dose of 50 kg each of P 2 O 5 and K 2 O ha -1 through SSP and MOP, respectively. All other crop management practices were followed as per the recommendations of aerobic rice culture.

2 application on yield The highest grain yield of scented rice under aerobic culture was produced with the 150 kg N ha -1 (N 3 ), which was however, comparable with 175 kg N ha -1 (N 4 ), but significantly higher than with 125 kg N ha -1 (N 2 ). This might be due to the reason that over dose of nitrogen of 175 kg ha -1 produced profuse tillering, which led to competition among them resulting in conversion of lesser number of tillers in to effective tillers and reduced the quantity of photosynthates from source to sink, which would have resulted in more number of ill filled grains there by finally reduced the grain yield. (Jadhav et al. 2004). The highest straw yield was recorded with175 kg N ha -1 (N 4 ), which was on par with the application of 150 kg N ha -1 (N 3 ), but significantly superior to 125 kg N ha -1 (N 2 ). Application of 100 kg N ha -1 (N 1 ) produced the lowest grain and straw yields. Regarding time of application of nitrogen, the highest grain and straw yields were recorded with (T 3 ) ¼ basal + ¼ at active tillering + ¼ at panicle initiation and ¼ at heading which was comparable to (T 4 ) ¼ basal + ¼ at active tillering + ¼ at panicle initiation and ¼ at flowering and significantly superior to other two split application schedules. This might be due to the application of nitrogen in splits according to crop requirement caused not only reduction in loss of nitrogen but also increased the nitrogen absorption, consequently better utilization of applied nitrogen. This was in accordance with findings of Balasubramanian (2002). The lowest yields were noticed with (T 1 ) ½ basal + ¼ at active tillering and ¼ at panicle initiation (Table 1). application on nutrient uptake Increased N uptake with application of increasing N levels from 100 to 175 Kg N ha -1 might be due to increased root growth that absorbs more N from the soil at higher N level resulting in higher nitrogen concentration in dry matter. The beneficial effect of increasing nitrogen levels on the nitrogen uptake was earlier reported by Saradeep Kour et al. (2005). Uptake of phosphorus and potassium were not significantly varied with nitrogen levels beyond 150 kg N ha -1. Nitrogen application at 150 kg N ha -1 absorbed higher phosphorus and potassium uptake. Increasing N application stimulated more vegetative growth and increased foraging capacity of roots which in turn increased the uptake of P and K. Similar results were observed by Rammohan et al. (1999). The uptake of all the three nutrients like N, P and K was the lowest with 100 kg ha -1 (N 1 ) (Table 2). Split application of N in four splits at ¼ th at basal + ¼ th at active tillering + ¼ th at panicle initiation + ¼ th at heading registered higher N, P and K uptake by the crop. The conjunctive and complementary effects of right dose and right time of nitrogen feeding to the rice crop might have been resulted in better root activity, there by enhancing the absorption of applied nutrients. Lowest value of N uptake with application of nitrogen scheduled in three splits upto panicle initiation (T 1 ), uptake of P and K was not influenced by time of N application. application on post harvest soil available nitrogen Supply of 175 kg ha -1, which failed to enhance seed yield had specific impact on post harvest available nitrogen due to higher dry matter production of roots which might have

3 added to the soil after their decay in organic form their by enhanced the mineralization of native nitrogen (Table 3). The time of nitrogen application failed to enhance post harvest available nitrogen significantly. This is because of complete uptake of applied nitrogen at each split and lesser mineralization of native nitrogen. CONCLUSION The study on the effect of levels and time of nitrogen application on yield, nutrient uptake and post harvest soil nitrogen status of scented rice under aerobic culture revealed that grain yield, uptake of phosphorus, potassium and post harvest soil available nitrogen of scented rice under aerobic culture recorded significantly highest values with 150 kg ha -1 nitrogen, the highest uptake of N was registered with 175 kg N ha -1. Application of nitrogen in four equal splits upto heading (T 3 ) resulted in the highest yields and uptake of N whereas uptake of P and K and post harvest status of soil available nitrogen were not influenced by time of N application. Table 1: Grain and straw yield (kg ha -1 ) of scented rice as influenced by levels and time of nitrogen application under aerobic culture Treatment Grain yield Straw yield Nitrogen levels (kg ha -1 ) N N N N SEm ± CD (P=0.05) Time of application T 1 ½ B + ¼ AT + ¼ PI T 2 1 / 3 B+ 1 / 3 AT+ 1 / 3 PI T 3 ¼ B+¼ AT+¼ PI + ¼ H T 4 ¼ B+ ¼ AT +¼ PI + ¼ F SEm ± CD (P=0.05)

4 Table 2: Uptake of nutrients and Post harvest soil available N status (kg ha -1 ) of scented rice as influenced by levels and time of nitrogen application under aerobic culture Treatment Nitrogen uptake Phosphorus uptake Potassium uptake Available Nitrogen Nitrogen levels (kg ha -1 ) N N N N SEm ± CD (P=0.05) Time of application T 1 ½ B + ¼ AT + ¼ PI T 2 1 / 3 B+ 1 / 3 AT+ 1 / 3 PI T 3 ¼ B+¼ AT+¼ PI + ¼ H T 4 ¼ B+ ¼ AT +¼ PI + ¼ F SEm ± CD (P=0.05) 5.0 NS NS 21.9

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