عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Background and objectives
Nitrogen (N), an essential nutrient for growth and development of plants, is added to agricultural fields to boost crop yields, however, its applications limited in the aquatic ecosystems due to leaching. Accordingly, accelerated surface water eutrophication, and public health issues due to consumption of contaminated groundwater have been linked to enrichment of excess use of N that can be lost to the environment through leaching to the groundwater. These losses can be reduced by adoption of appropriate methods or best management practices, that increase the accessibility of N for plant use, enhance plants’ N uptake ability, and match nutrient applications with agronomic needs. Thus, improving N use efficiency through a combination of agronomic and soil management methods is critical for crop profitability and environmental management.
One way to improve the efficiency of nitrogen fertilizer application and reduce its losses is the simultaneous use of organic and biological fertilizers along with chemical fertilizers. There are several ways to increase soil organic matter, but the most of these materials are not resistant to microbial decomposition and decompose quickly and lost from the soil. Biochar is one of the types of organic fertilizers, which is resistant to microbial decomposition.
Biochar can affect chemical and biological N reactions in the soils. Biochar increase nitrogen use efficiency (NUE), influence nitrification rates and adsorption of ammonia, and improve NH+ accumulation by enhancing cation exchange capacity in soils.
Nitration of groundwater due to improper use of chemical fertilizers and high leaching of nitrogen fertilizers and also low efficiency of nitrogen application in flood irrigation of rice, indicates the need for alternate management methods in rice cultivation, including changing irrigation methods and fertilizers types.. The use of biochar fertilizer along with nitrogen-fixing bacteria in rice irrigation rotation can be a good solution to reduce the mentioned problems.
Materials and Methods
This research was conducted at the research fields of the Sari Agricultural Sciences and Natural Resources University (SANRU) in 2017. The experimental site is located at 36º 39ʹ42ʺ N latitude and 53º03´54ʺ E longitude with -11 m above sea level. Soil samples were taken from depths of 0-30 cm before land preparation. The experiment was done in split split plot arrangement based a complete randomized blocks design with three replications. Two irrigation regimes (flooding and irrigation regimes) was the main plot. Nine fertilizers levels (100% of recommended nitrogen or N100, N100+ 10 ton biochar or biochar 10, N100+ biochar 20, N75, N75+ biochar 10, N100+ biochar 20, N50, N50+ biochar 10 and N100+ biochar 20) and seedling inoculation with Azospirillum lipoferum (without inoculation was also included as control) were sub and sub sub plots, respectively.
Results showed that biochar and nitrogen fertilizers, irrigation methods and also seedling inoculation with bacteria had significant effects on NUE, the amount of nitrogen and protein in the rice grains. Mean comparison of combination effects showed that consumption of 20 tons of biochar along with N50 or N75 had the greatest effect on NUE and the amount of nitrogen and protein in the grain, and the lowest amount of these traits was recorded in plots with N100 and no application of biochar. On the other hand, the highest level of nitrogen efficiency indices was obtained when 20 tons of biochar applied with N50 or N75 while the lowest amount of nitrogen use efficiency indices was obtained by using N100 and no biochar consumption.
It seems that biochar improves nitrogen uptake by the rice plant by maintaining nitrogen in the soil and consequently increases the concentration of nitrogen in the grains and rice plants organs. There was no similar trend for effect of biochar on nitrogen uptake when fertilizer application rates increased.