Uni-Bayreuth grafik-uni-bayreuth



Effect of polymers on plant residuals decomposition in agroecosystems


From 05/2009 to 02/2012

Principal Investigator: Yong Sik Ok, Yakov Kuzyakov
Staff: Yasser Mahmoud Awad
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

Soil erosion in highland agricultural systems reduces crop productivity and triggers eutrophication of surrounding watersheds due to the loss of nutrients such as phosphorous. This study was conducted to assess the effects of polymers (polyacrylamide [PAM] and biopolymer) that have been applied to prevent soil erosion on soil properties and on the growth of Chinese cabbage. Two types of commercial PAM (Soilfix G1 and Magnafloc 336) and one type of synthesized biopolymer (a copolymer of lignin, starch, acrylamide, and acrylic acid [LSAA]) were evaluated through a seed germination bioassay of Chinese cabbage (Brassica campestris L.) and pot experiments. The seed germination rates of the Chinese cabbage were 95-98% in the 0.5% and 1% polymer treated groups, which were similar to the control group (98%). Both groups of PAM and biopolymer promoted the growth of the Chinese cabbage (leaf length and width) when compared to the control group, and the fresh weight of Chinese cabbage was increased by 42-70% when compared to the control group. While 53% of the control group consisted of soil aggregates, the groups of Soilfix G1, Magnafloc 336, and biopolymer comprised 71, 73 and 66%, respectively. In addition, the lowest soil water retention was observed in the control group (45%), while this value was higher than other values from Soilfix G1, Magnafloc 336, and biopolymer treated groups (70, 65 and 67%, respectively). Both applications of PAM and biopolymer prevented soil erosion through improvement of the physiochemical soil properties and promoted the growth of Chinese cabbage as indicated by a pronounced increase yield.

Soil erosion and infiltration rate are major factors to crop productivity and upstream water quality. This study was conducted to determine if a copolymer of lignin, starch, acrylamide, and acrylic acid (LSAA) shows a significant reduction in soil loss from the laboratory experiments and to compare the effectiveness of LSAA and anionic polyacrylamide (PAM). To accomplish this, the ester group and carboxy group of the biopolymer were confirmed using FT-IR analysis because these groups are known to prevent soil loss with the interaction of soil particles. The applications of biopolymer and PAM at a rate of 200 kg ha-1 decreased soil loss by 98% and 96%, respectively, when compared to the untreated control.

Treatments of biopolymer and PAM induced no change in the pH from the runoff when compared to the untreated control, and these pH values did not exceed the criteria for water quality. Furthermore, the electrical conductivity (EC) of runoff was increased for all treated areas compared to the untreated control; however, these increases were not significant at 0.05 level. Total nitrogen (T-N) and total phosphorus (T-P) contents among biopolymer treatment groups were similar to these values from the untreated control. Conversely, the contents of T-N (3.29 mg L-1) and T-P (0.14 mg L-1) for PAM-treated area were greater than these contents for the biopolymer-treated area (T-N content of 2.74 mg L-1 and T-P content of 0.09 mg L-1). Our results suggest that biopolymers are an emerging alternative to PAM for reducing soil loss and contents of T-N and T-P in runoff. 


Acknowledgement: This work was carried out with the support of “Cooperative Research Program for Agriculture Science & Technology Development (Project No. PJ0074092010)” Rural Development Administration, Republic of Korea.

last modified 2012-11-27