Document Type

Thesis - Open Access

Award Date

2022

Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Navreet Mahal

Keywords

biochemical properties, kura clover, Physical properties, prairie cordgrass

Abstract

Prairie cordgrass (Spartina pectinata) (PCG) is a warm-season perennial grass that can be used as a biofuel feedstock and can be grown on marginal lands. Previous studies on intercropping of a perennial legume i.e., kura clover (Trifolium ambiguum) (KC) with PCG can improve soil biochemical properties, increase biomass production, mitigate greenhouse gas (GHG) emissions while reducing the chemical fertilizer requirement. However, there is a lack of evidence about the effects of PCG production on soil biochemical and physical properties during the cropping season and at deeper soil depths in reference to support plant growth, environmental implications and enhance the soil health of marginal lands. The overall objective of this study was to investigate the effects of PCG-KC intercropping on (1) soil biochemical properties at different sampling times during the season, and at different soil depths up to 60 cm, and (2) near-surface (0- 10 cm depth) hydro-physical properties. This field experiment was initiated in 2010 as a randomized complete block design with four replications of five treatments i.e., PCG intercropped with KC (PCG-KC), and PCG fertilized with different N fertilizer rates: 0 (PCG-0N), 75 (PCG-75N), 150 (PCG-150N), and 225 N kg ha-1 (PCG-225N). For seasonal biochemical properties assessment, surface soil samples were collected at 0-10 cm depth at three different times during the crop season: pre-emergence (PE), active growth (AG), and after harvest (PH) stages. To investigate the long-term effects on soil total carbon (TC) and total nitrogen (TN), deep soil cores were collected from 0-5, 5-15, 15-30, 30-45 and 45-60 cm depth after the crop harvest. The intact soil cores from 0-10 cm depth were collected at the AG stage to measure the soil physical properties. Overall, microbial biomass carbon (MBC) and nitrogen (MBN), and urease activity, were observed to be higher at the PE stage as compared to AG and PH stages. No treatment effect was observed for both MBC and MBN. Cold water-extractable C (CWC) showed a gradual increase from PE to AG to PH. Whereas, hot water extractable C (HWC), β-glucosidase activity, FDA, and glomalin, were highest at the AG stage and lowest at PE stage. The treatment effect was not significant for CWC, HWC and glomalin whereas, treatments had significant effect for all the enzymes, PCG-KC treatment had 45% higher mean β-glucosidase activity when compared to control (PCG-0), 56 and 42% higher mean urease compared to PCG-0 and PCG-75 N, and 13-19% higher FDA activity compared all other treatments. Total PLFA, bacterial, and fungal PLFA, CWN increased from PE to AG stage and showed similar or decreasing trend from AG to PH stages whereas HWN content decreased from AG to PH stage. Treatment effect was not significant for total PLFA and bacterial PLFA. There was a significant interaction between treatment and stage for CWN and HWN; PCG-KC showed higher mean values of CWN compared to PCG-0, PCG-75N and PCG-150N during the PE stage and was similar to all other N treatments except PCG-225N. PCG-KC had higher mean HWN when compared to control i.e., PCG-0 during AG stage and PCG-225N at PH stage. Nitrate concentration was higher at PE stage when compared to AG and PH stage which is contrary to the ammonium concentration that showed an increasing trend from PE to PH stage. Both the parameters had significant interaction between treatment and stage. The PCG-KC treatment had showed 34.3 and 24.4% lower nitrate concentration than PCG-150 and 225N during the AG stage and 24.3% lower than PCG-150N at PH stage. For ammonium PCG-KC treatment had a higher mean value than the control i.e., PCG-0 during PE stage and PCG-75N at PH stage. There was a gradual decrease in both TC and TN concentrations with soil depth. In the 0-5 cm layer, soil TC concentration was approximately 43% higher when compared to 45-60 cm soil depth. Similarly, TN concentration was approximately 83% higher in 0-5 cm soil layer when compared to deeper soil depth i.e., 45-60 cm. There was no treatment effect and its interaction with depth. The intercropping of KC with PCG had 0.024 cm3 cm-3 of macroporosity (MP), 50% higher Ksat, and 1% lower λ as compared to the other treatments. Moreover, PCGKC treatment had 1.42 g kg-1 of TN and 21.4 g kg-1 of TC in the surface layer which was comparable with PCG-75 treatment, however, were significantly higher as compared to the PCG-0. Overall, this study showed that the long-term maintenance of KC with PCG can provide soil health benefits through enhancing or maintaining the soil biochemical and hydro-physical properties. Therefore, long-term adoption of the perennial grass-legume system can enhance soil functional processes including, nutrient cycling, C sequestration, water storage, and availability, while maintaining biomass yields for biofuel production on marginal lands.

Number of Pages

112

Publisher

South Dakota State University

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Rights Statement

In Copyright