Soil Health Comparison in Organic and Conventional Cotton-Peanut Rotations in the Texas Plains Region

N. Boogades1, L. M. Ellman-Stortz1, K. Lewis2, T. Gentry1, P. DeLaune2
1Texas A&M University, 2Texas A&M AgriLife Research
Introduction
  • The purpose of this study was to investigate the effects of both cover crop use and management strategy on the ability of a system to utilize organic substrates for nutrient acquisition in the Texas plains, by measuring enzyme activities and carbon mineralization
  • The Texas Plains Region is a major producer of US cotton (Gossypim hirsutum) and peanuts (Arachis hypogea) and has emerged as a leader in organic production of these crops
  • Cover crops are an important nutrient management tool for organic producers due to restrictions on mineral fertilizer use
  • Measuring activities of enzymes involved in nutrient cycling, such as of N-acetyl-β-D-glucosaminidase (NAG) and β-glucosidase (BG) can indicate a system’s ability to mineralize organic nutrients and make them plant available
  • Mineralizable carbon (CMIN) is another indicator of a system’s ability to utilize organic substrates and is an estimator of soil biological activity
Materials and Methods
  • Locations: Texas A&M AgriLife Research Centers in Lubbock & Vernon, TX
  • Study Period: April-November 2020
    • Cover crops terminated April; peanuts planted in May
    • Data presented represents second phase of cotton-peanut rotation  
Spring 2019  *Fall 2019 *Spring 2020 * Fall 2020 Spring 2021  Fall    2021 **Spring 2022
Cotton Cover Crops Peanuts  Cover Crops Cotton Cover Crops Peanuts
*Study term of data presented in this poster
**Current status and first growing season under organic certification (3-year transitional period started in 2019)
  • Treatments
    • Main Blocks-conventional (conv) vs organic (org) production
    • Cover Crop Plot Treatments- rye (Secale cereale) (rye), radish (Raphanus sativus) (rad), rye/vetch (Vicia villosa) mix (rv), and rye/radish/vetch (rvr) mixes with conventional reduced-till control  
  • Soil Sampling: pre-plant (pre), mid-season (mid) and post-harvest (post) at 0-4 inches and 4-8 inches    
  • Meaured Parameters: 
    • β-glucosidase (BG) and N-acetyl-β-D-glucosaminidase (NAG) activity through colorimetric assays (Scott, 2019)                                                                                         
    • Mineralizable carbon (CMIN) determined during 3-day CO2 incubations (Franzluebbers, 2015)
Enzyme Activites
Enzyme data was pooled to include both depths because no depth interactions were seen at either location for either enzyme
 
β-glucosidase
  • Results were significant at Vernon only
  • Rye, rye-vetch and rye-vetch-radish treatments increased activity over fallow (Fig 1A)
  • Increased activity in organic compared to conventional and fallow treatments (Fig 1B) 
    
Figure 1. β-glucosidase enzyme activity at Vernon according to cover crop selection (A) and management (B). Bars within sample collection with the same letter are not different at P < 0.05 
 
N-acetyl-β-D-glucosaminidase
  • Significant results at both sites
  • Lubbock: greater activity in rye-vetch treatments compared to rye and rye-vetch-radish at post-harvest (Fig 2A)
  • Vernon: rye-vetch treatments had greater activity compared to rye and radish at pre-plant (Fig 2B)
    • Management: organic had greater activity during mid-season but conventional was greater post-harvest (Fig 2C)
Figure 2. N-acetyl-β-D-glucosaminidase enzyme activity at Lubbock according to cover crop selection (A), at Vernon according to cover crop selection (B) and at Vernon according to management (C). Bars within sample collection with the same letter are not different at P < 0.05
Mineralizable Carbon

Lubbock

  • Lubbock results only significant at 0-4 inch sampling depth
  • April: CMIN in rye plots were greater than fallow at 0-4 inch depths (Fig 3A)
    • Also in April sampling date: organic treatments had greater CMIN than fallow, but not conventional (Fig 3B)
  • September: CMIN was greater in rye-vetch treatments than in rye and fallow treatments (Fig 3A)
    • Also in September sampling date: greater CMIN in organic than in fallow, but not conventional (Fig 3B)

Vernon

  • Vernon results significant at both depths, but only according to management 
  • April: Conventional CMIN was greater than organic and fallow, at 4-8 inches (Fig 3D)
  • July: Organic was greater than conventional and fallow at both depths (Fig 3C&D)
  • September: Both organic and conventional were greater than fallow, but did not differ from each other at 0-4 inches (Fig 3B)
 
 
 
Figure 3. Mineralizable carbon at Lubbock according to cover crop at 0-4 inches (A), managment at 0-4 inches (B) and at Vernon according to management at 0-4 inches (C) and 4-8 inches (D). Bars within sample collection with the same letter are not different at P < 0.1 
Conclusion
Cover crop presence and management strategy have potential to enhance soil enzyme activities and carbon mineralization, both of which are important for nutrient cycling in systems dependent on organic inputs as nutrient sources. Organic management generally increased both factors over conventional and fallow management, while cover crops, legumes and nonlegumes, also resulted in increased nutrient cycling parameters. Further research should examine the sustainability of organic systems in the Texas Plains Region and evaluate the viability of organic nutrient management strategies relying on factors such as enzyme activity and carbon mineralization to enhance crop nutrient availability.
 
References 
 
Franzluebbers, A. 2015. Should Soil Testing Services Measure Soil Biological Activity? Agricultural and Environmental Letters.
 
Stott, D.E. 2019. Recommended Soil Health Indicators and Associated Laboratory Procedures. Soil Health Technical Note No. 450-03. U.S. Department of Agriculture, Natural Resources Conservation Service.
 
Texas Highways, The wildflower regions and vegetational areas of Texas. (2020, March 17)  https://texashighways.com/wildflowers/the-wildflower-regions-and-vegetational-areas-of-texas/