Dissertation

Integrating Compost and Crop Intensification for Sustaining Soil Health and Water Storage in Semi-Arid High Plains Agroecosystems

Adebayo, Olufemi O

2025

Overview

Soil degradation and limited water availability are major constraints to crop production in semi-arid regions. Researchers and policymakers have promoted cropping system intensification through cover cropping and compost application as promising strategies to enhance soil fertility, enhance water regulation, and overall agroecosystem resilience. However, their combined effects on nitrogen (N), soil water dynamics, soil health, and aggregate-associated carbon (C) and N storage in soil aggregates and overall soil health remain poorly understood in water-limited systems. A study was conducted to i) optimize soil inorganic N extraction methods for assessing plant-available N, ii) evaluate compost and cover crop impacts on soil water storage, evapotranspiration, and crop water productivity, iii) identify biological, biochemical, and physical indicators of soil health that are both management-sensitive and functionally linked to soil water functions across intensification strategies iv) quantify soil C&N storage across various aggregate classes and their linkages with sorghum yield.Cropping system intensification, which involves increasing the diversity, frequency, or biomass production of crops within a rotation, has been promoted as a strategy to sustainably improve productivity and resource use efficiency. This approach aims to enhance soil fertility, improve water regulation, and strengthen overall agroecosystem resilience without expanding cultivated land. Cover cropping, a key form of cropping system intensification, has emerged as a particularly promising strategy to build soil health in semiarid systems. Cover crop treatments at Clovis included pea (Pisum sativum L.), oat (Avena sativa L.), canola (Brassica napus L.), mixtures of pea + oat (POM), pea + canola (PCM), pea + oat + canola (POCM), a six-species mixture (SSM; pea + oat + canola + hairy vetch; Vicia villosa Roth + forage radish; Raphanus sativus L. + barley; Hordeum vulgare L.), and a no-cover crop (NCC). Compost was also evaluated as a complementary management practice, applied at 16.8 Mg ha⁻¹ or not applied (0 Mg ha⁻¹). As a rich source of organic matter and nutrients, compost has the potential to stimulate microbial activity, improve soil structure, and enhance water storage. Together, cropping system intensification and compost represent complementary approaches that, when integrated, strengthen soil health and water management in water-limited environments. Soil samples were collected during the summers of 2022–2024. In Chapter 3, the study further expanded to Akron, CO, where compost was applied at 22.9 Mg ha⁻¹ under two crop rotations: wheat/forage pea and wheat/fallow. This dual-site design allowed for evaluating the combined effects of compost and cropping system intensification across contrasting semiarid environments and management histories, thereby supporting the development of a soil health framework for water-limited environments.The first two objectives were focused on water and nitrogen use efficiency. In the first study, we compared the N extraction efficiency of five approaches: distilled water (DW) at room temperature (25 °C), and 1 M and 2 M KCl extractions conducted either cold (25 °C) or hot (100 °C for 4 h). Results showed that hot 1 M KCl extraction best captured compost-enhanced N availability, particularly during peak growing periods, extracting 25–440% more inorganic N than cold 1 M KCl in compost-amended soils. However, no difference was observed between cold and hot 1 M KCl extractions prior to compost application. Compost consistently increased inorganic N compared to no compost. The second objective was focused on the evaluation of three cover crop treatments (fallow, pea, and SSM) with and without compost in the sorghum (Sorghum bicolor L. Moench) phase of a winter wheat (Triticum aestivum L.)–sorghum–fallow (WSF) rotation showed that compost increased soil water content and boosted sorghum yield by 22–29% compared to no compost, thereby improving CWP. The diverse mixture (SSM) conserved more water at sorghum harvest but depleted water earlier in the season due to greater demand, whereas pea and NCC showed smaller seasonal changes. Two years of observations and simulations with the Root Zone Water Quality Model 2 (RZWQM2) supported these findings, with the model reproducing field dynamics and achieving RMSE values of 0.02 to 0.05 cm³ cm⁻³ for soil water and 1.12 to 3.22 °C for soil temperature.The third and fourth objectives were focused on soil health assessment and their linkages with key ecosystem functions. For example, range of physical, chemical, and biological indicators of soil health was compared under varying cropping intensities and compost amendments at two semi-arid locations (Clovis, NM and Akron, CO) in the third objective. The results showed strong effects of compost on multiple soil properties. Compost application increased microbial abundance by 63–268%, particulate organic matter-C by 211%, mineral-associated organic matter-C by 63%, and enhanced labile C and inorganic N relative to no-compost. These effects were more pronounced at the long-term compost site. Cover cropping, particularly with diverse mixtures, modestly improved microbial activity and arbuscular mycorrhizal fungi abundance, with stronger responses when combined with compost. While some indicators exhibited site-specific sensitivity, the most consistently responsive across both sites were potentially mineralizable C, total fatty acid methyl esters (FAME), and total labile N. Principal component analysis further identified FAME, total labile N, particulate organic matter-C, and saturated hydraulic conductivity as the minimum data set indicators for semi-arid environments. The fourth objective focused on soil aggregate dynamics and was evaluated across the full set of eight cover crop treatments (fallow, pea, oat, canola, POM, PCM, POCM, and SSM) with and without compost. Findings indicated that compost increased soil organic carbon (SOC) across all aggregate size classes, with 8–11% greater SOC in mineral-associated fractions, and shifted the distribution toward microaggregate and mineral fractions, promoting SOC stabilization, although soil organic nitrogen declined. Compost also modestly increased sorghum yield by 14% in 2023 and 4% in 2024, while cover crop effects were limited.Overall, this study demonstrated that compost is the primary driver of soil health improvements in semi-arid systems, consistently enhancing nutrient cycling, microbial activity, water retention, and SOC stabilization. Cover crops contributed modest, context-dependent benefits shaped by species composition and seasonal water use. Integrating compost with cropping system intensification offers a sustainable pathway to enhance soil functions, improve productivity, and strengthen the resilience of water-limited agroecosystems.

• Publisher: ProQuest Dissertations & Theses
• Subject: Environmental science / Plant sciences / Soil sciences
• ISBN: 9798265471277