An Evaluation of Short-Term Effects of Different Soil Management Systems on Soil Physical, Structural and Hydraulic Properties and an Estimation and Optimization of Water Infiltration for Layered Domains Using a Restructured Green-Ampt Model in an Agricultural Terrain, Lebanon

Abstract

Soil management systems are widely used in agricultural systems due to their diverse functionality in enhancing water infiltration, soil aggregate stability, and ultimately crop yield. In this regard, each system provokes alteration to the soil physique. Such changes are sometimes reported as contradicting. Consequently, choosing a system to enhance water infiltration in an agricultural terrain seems site-specific. Nevertheless, implementing all management systems to determine water infiltration capacities for a specific site can be costly and time-consuming. Hence, the need for a mathematical model that computes infiltration into agricultural soils is necessary. As this stands, this study attempt to solve three questions: (1) what are the changes and their significance that the soil management systems impose on soil properties? (2) which mathematical model is best used to compute infiltration in layered agricultural soils under different irrigation rates while taking into consideration ponding effects? (3) what is the best soil management system to be implemented in loamy sand agricultural land that is cultivated by apple trees and legumes and vegetables in-between rows to carry water to depths of 40cm faster with less water consumption while maintaining the subsurface moisture for longer periods? The first part includes the determination of soil properties. Two sites are chosen: loamy sand and clay loam soils. Five management systems were implemented: NT (no-tillage), CC+NT (cover crop), MC+NT (chicken manure cover), RT+NT (tilled soil by rotation using a tractor), MTA+NT (tilled soil mixed with chicken manure), and MT+NT (tilled soil mixed with crop residues). The organic matter content, the aggregate size distribution, the densities (in addition to porosities and residual moisture content), and the saturated hydraulic conductivities were measured in the laboratory using the loss on ignition, sieve analysis, coring, and constant head permeability methods, respectively while the pore structure was analyzed from CT-scan images of undisturbed samples. In both soils, tillage application decreased the densities, the aggregate mean weight diameter, the residual moisture content, and the fine pore volumes while increased the organic matter content, the porosity, the saturated hydraulic conductivity, and the amount of large pores of undisturbed soil. Likewise, the addition of organic matter supplemented the behavior of RT. In loamy sand soils, NT layer proved to be more adequate for maximum crop production, to have good air capacity for soil aeration while maintaining a better storage for subsequent use of water, and to maintain a good aggregate stability. Albeit the rotary tilled layer had a similar good structure and environment for soil aeration to NT, it lacked the qualities to maintain water and to structurally hold water for plant growth. However, the addition of organic matter enhanced such qualities with some limitations. The advantage of tilled layers over undisturbed soils is the better conductivity of water due to larger and better sorted pores. However, in clay loam soils, NT lacked all criteria for good physical quality indications in opposition to RT. Even the addition of organic matter was not shown to be advantageous as the large pores found in RT were further decreased by the deposition of the organics. Notwithstanding, the role of organics was consistent in improving the water conductivity. Yet, the crop residues proved to be highly adsorptive to water and tend to activate preferential flow while chicken manure is more conductive. The second part included the derivation of the mathematical model which resulted in good Nash-Sutcliffe Efficiency. For irrigation rate smaller than 0.05cm/min, NT was faster since all the other systems had larger pore structure for which more time is needed to saturate. For higher irrigation rates, systems have only tilled layer are more efficient especially those amalgamated with chicken manure. Hence, it is recommended to use crop residues as soil covers in case of ponding irrigation. Finally, the third part resulted in having MTA+NT as the optimal system in loamy sand soil in which the addition of artificial macropores filled with straw residues would enhance water storage and drainage.