Infiltration, soil moisture, root rot and nematode populations after 12 years of different tillage, residue and crop rotation managements

Abstract

Tropical and subtropical highlands of the world have been densely populated and intensively cropped. Agricultural sustainability problems resulting from soil erosion and fertility decline have arisen throughout this agro-ecological zone. We assessed practices that would sustain higher and stable yields for wheat (Triticum aestivum L.) and maize (Zea mays L.) in this region. A long-term experiment (randomized complete block) was started in 1991 under rainfed conditions in the volcanic highlands of central Mexico (2240 m a.s.l.;19.31°N, 98.50°W; Phaeozem). Our objective was to determine infiltration, soil moisture content, root diseases and nematode populations at the end of 12 years of 16 management treatments from a factorial arrangement of: (1) four rotations (monocropping and rotation of maize and wheat), (2) two tillage (conventional tillage [CT] and zero tillage [ZT]) and (3) two crop residue management practices (residue retention and removal). Water infiltration and soil moisture levels were greater under ZT when residue was left in the field then when residue was removed. Higher infiltration rates and favourable moisture dynamics supported up to 30% yield increase. A significantly higher incidence of root rot was found in monoculture of maize under ZT than CT. Residue retention significantly increased maize root rot incidence compared to residue removal. Rotation of maize and wheat decreased the incidence of maize root rot up to 30%. In general, the incidence of root disease was lower in wheat (up to 3 on a scale of 7) than in maize (up to 3.93 on a scale of 4) for all treatment. In maize, both non-parasitic and parasitic nematodes increased under ZT; however, in wheat no effect of tillage was seen. Incidence of root rot and parasitic nematode populations were not correlated with yield. Although root diseases may have affected crop performance, they affected yield less than other critical plant growth factors such as infiltration and water availability. Both environmental conditions and microflora played a key role in the biology and expression of soil pathogens. In the semi-arid and rainfed subtropical highlands of central Mexico, positive effects were observed with zero tillage, crop rotations and crop residue retention, compared with common farming practices.

Introduction

A number of technical innovations (zero tillage, appropriate crop rotations and residue management) could improve the productivity and biophysical sustainability of sub-tropical highland cropping systems. The sub-tropical highlands of Central Mexico, are densely populated and have been intensively cropped for centuries. Problems related to soil erosion from wind and water, and declining soil fertility threaten the sustainability of agriculture throughout this agro-ecological zone (Scherr and Yadav, 1996). Periodic drought and periodic water excess are other major constraints.

Water is the primary constraint to crop production in semi-arid regions. Approximately 40% (600 Mha) of the world's cropland area is affected by low and unpredictable rainfall, with 60% of these lands located in developing countries (Johnston et al., 2002). Zero tillage (ZT) combined with crop residue retention on the soil surface, can improve moisture infiltration (Shaver et al., 2002), and greatly reduce erosion and enhance water use efficiency (Johnston et al., 2002) compared to conventional tillage (CT). Crop residues on the soil surface form a barrier to water loss by evaporation, increasing the amount of moisture stored in the plant root zone and available to the crop. Field research has shown higher moisture levels, decreased soil temperatures and also more stable soil aggregates (i.e., improved soil structure) under ZT compared to CT (Carter, 1992).

Changes in tillage, residue management and rotation practices induce major shifts in soil properties and number and composition of soil fauna, including both deleterious and beneficial organisms. A reduction in tillage influences various pathogens in different ways, depending on their survival strategies and life cycles (Bockus and Shroyer, 1998). Species that pass one or more stages of their life cycle in the soil are most directly affected by tillage. A review of 45 studies (Stinner and House, 1990) showed that 28% of the pest species increased with decreasing tillage, 29% showed no significant influence of tillage and 43% decreased with decreasing tillage. When ZT and crop residue retention are combined, residue-borne pathogens and beneficial species have substrates for growth and pathogens are positioned at the soil surface, where spore release may occur. Modifications to the microenvironment influence the biological activity of beneficial and pathogenic micro-organisms in both the crop canopy and in the soil. Crop rotation may reduce pathogen carryover on crop residues or in the soil. Reduced tillage indirectly defines the species composition of the soil microbial community by improving retention of soil moisture and modifying soil temperature (Krupinsky et al., 2002). Enhanced surface-soil microbial activity accompanying reduced tillage may create an environment that is more antagonistic to pathogens due to competition effects (Cook, 1990). The cooler soil temperatures associated with reduced tillage may favour such antagonistic soil microbial populations (Knudsen et al., 1995). Tillage systems have the potential to alter inoculum density of a pathogen and its ability to survive (Bailey and Lazarovits, 2003).

The most common root rot pathogens found on cereals under zero tillage systems (Bockus and Shroyer, 1998, Paulitz et al., 2002) are: take-all, caused by Gaeumannomyces graminis (Sacc.) Arx & Olivier var. tritici I Walker; Rhizoctonia root rot and bare patch caused by Rhizoctonia solani Kühn AG 8; Pythium damping-off and root rot caused by Pythium aphanidermatum (Edison) Fitzp and other species of the same genus; Fusarium crown, foot and root rot caused by Fusarium culmorum (W.G. Sm.) Sacc; F. pseudograminearum O’Donnell et T. Aoki and other species belonging to the genus Fusarium (Paulitz et al., 2002); common root rot caused by Bipolaris sorokiniana (Sacc.) Shoem. (Wildermuth et al., 1997, Mathre et al., 2003). In the highlands of central Mexico under semi-arid conditions, pathogens most frequently isolated from wheat roots were B. sorokiniana, Fusarium spp., and G. graminis var. tritici and from maize roots were Fusarium spp., Pythium spp. and Rhizoctonia spp. (Lawn and Sayre, 1992, Mezzalama et al., 1999).

Nematode densities range from 2 × 10⁵ individuals m⁻² in arid soils to more than 3 × 10⁷ individuals m⁻² in humid ecosystems (Barker and Koenning, 1998). Although a number of plant parasitic nematodes are reported to be associated with wheat, only a few species are economically important. In surveys conducted in Mexico, Pratylenchus thornei was found to be an economically important species, resulting in yield losses up to 40% (Lawn and Sayre, 1992, Nicol and Ortiz-Monasterio, 2004). More then 60 nematode species, among them P. thornei, are reported to be associated with maize in different parts of the world (McDonald and Nicol, 2005).

Since 1991, a rainfed experiment has been conducted by the International Maize and Wheat Improvement Center (CIMMYT) in the central volcanic highlands of Mexico to generate information concerning the enduring effects of tillage/seeding practices, crop rotations and crop residue management on the performance of maize and wheat. The aim was to identify practices that would promote high, sustainable maize and wheat yields in the target environment. Our objectives were to determine the effect of different tillage levels (CT and ZT), crop residue management (removal versus retention) and different crop rotations on infiltration, moisture content, incidence of root rot and nematode populations.