Element cycles in mountain regions under differing land use


From 03/2009 to 09/2012

Principal Investigator: Yakov Kuzyakov, Jae E. Yang, Yong Sik Ok
Staff: Janine Kettering
Grant: IRTG 1565 WP II TERRECO - Complex Terrain and Ecological Heterogeneity - Evaluating ecosystem services in production versus water yield and water quality in mountainous landscapes

Abstract N Budgeting 2011: Excessive N fertilization and the heavy monsoon rains together with predominantly sandy soils in Haean Catchment (South Korea) are predestined for high N losses during the cropping season leading to environmental pollution. The purpose of this study was to relate the fertilizer N inputs into the soil under intensive agriculture to the outputs on field scale as well as on catchment scale. We measured the contribution of agricultural fields to the N export during the monsoon season by creating N budgets for the most important crops and soil types considering various landscape parameters. We identified typical amounts of N accumulation in soil and plants, N removal with harvest, and fertilizer N use efficiencies by crops. The field budgets were up-scaled to catchment level (64 km2) and a general budget with amounts of N uptake, N retention and N loss was calculated. By using an ANCOVA, we determined parameters responsible for dissimilarities/similarities in fertilizer N use efficiency as well as in the N budgets on field scale. Finally, we aim to identify potential savings and give recommendation for a best practice and sustainable agriculture.

All N budgets were positive, with N inputs exceeding outputs for around 2.2 times. N net accumulation at field scale is found to be highest for rice paddies (240 kg N ha-1) and lowest for soy bean (81 kg N ha-1). At catchment level, rice and radish play the most important role for N export with 120 t and 80 t per cropping season, respectively. The highest N crop use efficiency shows bean (74%), whereas the NUE for rice is with 30% the lowest of all investigated crops. Radish (51%), cabbage (53%) and potato (46%) lie within the common range of 40-60% for upland crops.

Keywords: catchment N budgeting, N surplus and leaching, N retention, sandy soils, summer monsoon, fertilizer N use efficiency, up-scaling


project description in detail from proceedings of 2011 TERRECO Science Conference GAP


Abstract N Leaching 2011: Excessive N fertilization and the heavy monsoon rains during the cropping season together with predominantly sandy soils in Haean Catchment (South Korea) are predestined for high N leaching losses leading to water pollution. The purpose of this study was to investigate the dynamics of N loss with leaching in intensive dryland cropping systems with ridge-cultivation and plastic mulching. We investigated (1) the fate of fertilizer N, (2) the residual effect of N in the soil profile, and (3) the N downward movement with percolation, using the 15N fertilizer method in a summer radish system under conventional management. Since N leaching was not expected during the dry and cold winter, we conducted the field experiment during the cropping season. In order to determine optimal gains in ecosystem services, namely production of agricultural crops versus limited impacts on water quality, N dynamics were examined within a range of fertilization levels ranging from 50 to 350 kg N ha-1. New elements of this experiment were 1) the dicotyledonous root crop species, 2) the adaption of local farming methods of ridge-cultivation and plastic mulching, and 3) the heavy rains of the East-Asian summer monsoon. A similar biomass production compared to the highest fertilizer application rates, but with a notably higher recovery of tracer and fairly lower nitrate concentrations in seepage over the cropping season was shown by rate N150.

Keywords: N leaching, N retention, sandy soils, summer monsoon, N use efficiency, stable isotope, suction lysimeter


project description in detail from proceedings of 2011 TERRECO Science Conference GAP


Biomass development, N budget, and N use efficiencies in an agricultural catchment under monsoon climate

Abstract 2013: Balanced N cycles as well as high nitrogen use efficiencies (NUE) in agricultural-based systems are critical to ensure short-term productivity together with long-term sustainability as they underpin ecosystem services such as crop production and water quality maintenance. To aid in reducing agricultural non-point source pollution, a nitrogen (N) budget analysis was conducted for the five key crops of Haean catchment, which related fertilizer N inputs into soil to N outputs at both field and catchment scale. The N budget of all investigated crops was positive, with total N inputs exceeding N outputs by an average of 2.8 times. At the catchment scale, agriculture contributed over 90% to the maximum N surplus (473 Mg). Rice and radish, with over 100 Mg N surplus each, contributed the largest part. 

N budgets additionally provide an assessment of NUE and show when the potential for N surpluses are high. Radish showed the highest NUE (ca. 45%), whereas rice showed a significantly lower efficiency (24 to 30%). Bean, cabbage and potato efficiencies were found to range between 39 to 43%. Mean NUE of the five key crops of the catchment support earlier findings, which found the NUE of crops grown in South Korea to be the lowest in Asia at 38%. On average, 65% of the mineral N fertilizer was applied prior to planting, which made it vulnerable to N losses, especially early in the season. Additionally, the applied fertilizer N rates in the Haean Catchment exceeded the recommendations given by the RDA (Rural Development Administration) by 2.3, 1.5 and 1.2 times for rice, potato and cabbage, respectively. Because fertilizer N was the major N input (>50%) for all crop types except soybean, its reduction was identified as the major scope of action for N savings as well as for increasing NUE. Further measures like multiple fertilizer applications, application timing to match crop needs, and use of cover crops during the fallow period would complement these measures.

Using 15N, we investigated in detail the NUE of radish together with biomass development over a growing season. NUE and biomass were examined at fertilizer N application rates from 50 to 350 kg N ha-1. The lack of significant differences in dry matter (DM) production between N150, N250 and N350 indicates that similar crop yields can be achieved with lower fertilizer N rates. While the significantly lower DM production at N50 implies that an N addition of at least 150 kg N ha-1 is required to achieve maximum biomass production. NUE at the first sampling day (day 25) were found to be very low: 3.8% (N150) > 3.7% (N50) > 2.7% (N250) > 1.7% (N350). The highest NUE of all sampling days was observed at day 50 at N50 and N150, and accordingly, no significant increase of NUE occurred in the final 25 days of growth at these rates of application. These findings suggest that most of the fertilizer N was lost by day 50 at the lower application rates. A significant increase of NUE during the days 50 and 75 was recorded at the N addition rate N350. However, because the fertilizer N addition rate did not have a significant effect on the final NUE, a majority of the fertilizer N was taken up by the plant and used for biomass production in the first 50 days of growth at all fertilizer N rates. This was consistent with the fact that no significant biomass production was observed in the last 25 days of growth at any of the four N addition rates. We therefore propose multiple fertilizer applications in total of 150 kg N ha-1 which equals a N reduction of 40% compared to the current recommendation of the RDA.  

Keywords: radish cultivation, nitrogen use efficiency, N budget, fertilizer N, biomass development, best management practices

Homepage: http://www.aes.uni-bayreuth.de/aes/de/mitarbeiter/mit/mitarbeiter_detail.php?id_obj=68193

List of publications of this Project

Berger, S; Kim, Y; Kettering, J; Gebauer, G: Plastic mulching in agriculture - friend or foe of N2O emissions?, Agriculture, Ecosystems & Environment, 167, 43-51 (2013), doi:10.1016/j.agee.2013.01.010 -- Details
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