Defining tillage need for edible bean production under no-tillage: Classical and time series analyses
Introduction
Edible beans are grown in over 23 million hectares around the world. Brazil is the largest producer (3.4 million ton) with high per capita consumption (15 – 18 kg beans hab−1 yr−1) (CONAB, 2013), with an average yield of about 1 ton ha−1, although yields above 3 ton ha−1 can be achieved in irrigated crops and with high technological level of production.
Edible beans have their growth and yield dramatically affected by climatic variations, light sensitivity, and soil water stress during the growing season. In southern Brazil, the bean growing cycle is about 90 days, demands 300-mm of water and requires high-fertility soil (CEPEF, 2000). Soil physical and chemical conditions also indirectly affect bean growth by disturbing rhizobia efficiency in nitrogen fixation (Soares et al., 2016; Mercante et al., 2017).
Intense traffic of agricultural machinery in no-tillage systems lacking crop rotation and cover crops increase soil bulk density and penetration resistance (Lima et al., 2010), which reduces root growth of black beans (Kaiser et al., 2009) and limits air and water flow and crop access to water stored in soil (Mentges et al., 2016; Reichert et al., 2016). From beans flowering to grain filling, water deficiency affects root growth and yield components of common bean (Collares et al., 2006), especially in high-temperature periods (da Silva et al., 2006).
No-tillage systems with cover crops in succession and rotation, on the other hand, may improve soil aggregation (Wohlemberg et al., 2004), increase biopores and water infiltration (Abreu et al., 2004), and soil moisture and organic matter (Horn and Fleige, 2009; Reichert et al., 2016), whereas mulch in this system promotes greater water retention and availability to plants (Reichert et al., 2015b), reduces evapotranspiration (Stone et al., 2006), and increases soil resistance to deformation (Braida et al., 2008; Reichert et al., 2014; Holthusen et al., 2018b), thus improving the supply of water and nutrients to increase bean yield (Ferreira et al., 2011).
Shallow bean root penetration, and root and leaf diseases are found in compacted NT soils (Collares et al., 2008). Soil tillage by ploughing or chiseling of no-till soil reduces the degree of compaction temporarily, but soil may reconsolidate in less than one year (Reichert et al., 2009b). Therefore, reduced compaction may not necessarily increase yield as observed for soybeans (Secco et al., 2009).
Since a single indicator of soil quality for crop production may be misleading (Letey, 1985), an integrated approach - the least limiting water range (LLWR) - was proposed (da Silva et al., 1994) and extensively used, particularly in Brazil, to evaluate soil physical quality (e.g. Moreira et al., 2014; Miola et al., 2015; Watanabe et al., 2018) and the concept has been applied in soil fertility studies (e.g. Bortolanza and Klein, 2016). Nonetheless, only a few have actually related LLWR to crop physiology (Mohammadi et al., 2010), root development (Kaiser et al., 2010) or yield (e.g. Gubiani et al., 2013; Júnnyor et al., 2015; Garbiate et al., 2016).
The four limits of the LLWR are related to crop yield, but their determination using fixed values marginalizes actual functioning of the system (De Jong van Lier and Gubiani, 2015). Using LLWR as a physical property related to crop stree is still controverse in the literature (e.g. Gubiani and Metnges, 2020), with limited relation of soil functioning to crop growth and yield. Thus, besides studying soil functioning properties (Reichert et al., 2017; Holthusen et al., 2018a), spatio-temporal analysis is also a tool to improve our understanding in systems response (Awe et al., 2014, 2015; Reichert et al., 2015a).
The spatio-temporal analysis of soil hydro-physical processes and their relationship with other soil and atmospheric properties have received considerable attention in recent time (Timm et al., 2011; Jia et al., 2013; Awe et al., 2014). The temporal variability of soil water status and relationship with other atmospheric variables, for instance rainfall (Timm et al., 201), air temperature (Awe et al., 2015; Reichert et al., 2015a) and potential evapotranspiration (Awe et al., 2014), have been studied for some soil management and cropping systems. Rainfall and potential evapotranspiration were significantly related to soil water storage in a study of temporal variability of soil water storage in coffee field (Timm et al., 2011).
Soil water storage showed significant temporal variability in all the soil layers of a sugarcane field revealing a significant relationship with potential evapotranspiration and rainfall (Awe et al., 2014). Temporal distribution of soil available water in a common bean field did not correlate with daily rainfall but correlated with air temperature. The time-series analysis showed that plant-available water was significantly related to both rainfall and air temperature (Reichert et al., 2015a). These studies show that only a few crops and limited soil management systems have been explored, and thus there is opportunity for considering the vast varieties of crops grown and diverse soil management options, particularly for staple food in the subtropics and tropics.
The objectives of this study were to investigate the effect of tillage on changes in soil physical properties, number of days that the soil moisture is outside the critical limits of the LLWR, crop root distribution and black beans yield; and temporal processes of soil water content and temperature in compacted no-till and tilled soil and relationship with other soil-atmospheric variables.
Section snippets
Site description and soil properties
The experimental site is located at latitude 29° 41′ S, longitude 53° 48′ W and altitude, 95 m above mean sea level. Climate is humid subtropical with temperatures during warmest month higher than 22 °C and during the coldest month with −3 °C. The soil is classified as Acrisol by WRB (2006), and Argissolo Vermelho Amarelo distrófico by SiBCS (EMPRESA BRASILEIRA DE PESQUISA AGROPECUÁRIA - EMBRAPA, 2006). Soil granulometric composition for the 0.00 – 0.40 m depth was 650 g kg−1 sand, 230 g kg−1
Soil water content and the mechanical impediment to root growth
Throughout the bean crop cycle (Fig. 2), low mechanical resistance to penetration (PR) was observed in the 0.03 – 0.05 m soil layer, especially during the first 10 days after beans were sown. Soil PR was greater in NT than in Plo or Chi tillage, but always below 1.5 MPa. In NT, soil PR was greatest during the bean cycle in 0.06 – 0.10 m layer. The highest amplitude in PR occurred for 0.12 – 0.20 m layers due to higher variations in soil moisture, with PR above 2.5 MPa for the three soil
Classical statistics
Among several soil properties that influence penetration resistance (PR), soil bulk density (ρb) and particularly soil moisture is highly variable during the crop cycle. Lowest soil moisture during the bean cycle was observed close to harvest, which resulted in high soil strength, when the crop was at physiological maturity. The 0.075 - 0.015 m soil layer usually has the greatest compaction (highest ρb) under no-tillage conditions, called “no-tillage pan” (Reichert et al., 2009a). Reinert et
Conclusions
The number of days in which the soil was in better moisture conditions follow the order in tillage treatment plough ≈ chisel > no-tillage. Although tillage of compacted, long-term no-tillage improves soil physical conditions, inverting and non-inverting tillage of soil previously under no-tillage do not increase in crop yield. Thus, both the degree-of-compactness and the least limiting water range do not capture soil physical quality to beans growth and yield. The low soil thermal diffusivity
Declaration of Competing Interest
The authors hereby declare no conflict of interest.
Acknowledgments
This study was financed in part by the “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior” (CAPES) - Finance Code 001, the Brazilian Council for Scientific and Technological Development (CNPq), and “Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul” (Fapergs).
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