Fertilization and tillage effects on soil properties and maize yield in a Southern Pampas Argiudoll

Abstract

Agricultural management practices, such as tillage and fertilization alter soil physical, chemical and biological properties over the medium term, which has a direct impact on the system's sustainability and crop performance. The aim of this work was to evaluate how fertilization with nitrogen (N), phosphorus (P), sulphur (S), micronutrients (Mi), liming (Li) and tillage systems affect soil properties in the medium term, and to measure the impact of these changes on maize (Zea mays L.) yield.

A seven-year experiment on a Typic Argiudoll in the Southern Pampas region of Argentina using seven fertilizations treatments (Control, N P, NS, PS, NPS, NPS + Mi, and NPS + Mi + Li) and two tillage systems – conventional tillage (CT) and no-till (NT) – was evaluated. Each sub-plot was analyzed to determine physical parameters – bulk density (BD) and aggregate stability (AS)-, biological parameters – total organic carbon (TOC), carbon in the particulate fraction (COP), anaerobically incubated nitrogen (AN), total nitrogen (TN) and nitrogen in the particulate fraction (PN) – and chemical parameters – nitrate, available phosphorus, sulphate and pH – at different depths. Also, maize yield was measured in the final year without fertilizer application, in order to evaluate the effects of soil changes on this crop.

Among the physical parameters, the only differences found were in BD between tillage systems in the 0–5 cm layer (1.28 g cm⁻³ in NT and 1.15 g cm⁻³ in CT). Biological parameters were unaffected by fertilization treatments. However, tillage systems modified many of them in the 0–5 cm layer: COT (17 Mg ha⁻¹ in CT and 21 Mg ha⁻¹ in NT), POC (2.4 Mg ha⁻¹ in CT and 4.5 Mg ha⁻¹ in NT), TN (1.4 Mg ha⁻¹ in CT and 1.8 Mg ha⁻¹ in NT), PN (0.3 Mg ha⁻¹ in CT and 0.5 Mg ha⁻¹ in NT) and AN (56 mg kg⁻¹ in CT and 79 mg kg⁻¹ in NT). These differences were not significant when the 5–20 cm depth was analyzed. Chemical properties such as pH (5.7 in treatments with N; 6.1 without N, and 6.4 with N and lime) and P Bray content were modified (35 mg kg⁻¹ in treatments with P and 13 mg kg⁻¹ without P). In both cases, there was interaction with the tillage system, with significant stratification under NT.

Maize yield was only affected by residual P; there were no other effects of medium-term fertilization or tillage systems.

Introduction

The Argentinean Southern Pampas region, due to its edaphic and climatic properties, is considered one of the areas with the highest agricultural potential in the world (Satorre and Slafer, 1999). However, the use of intensive crop production and traditional management practices has diminished the physical, chemical and biological properties of the soil (Echeverría and Ferrari, 1993). This degradation process is related, among other factors, to the use of aggressive tillage systems (Steinbach and Alvarez, 2005), while other management practices, such as no-till and fertilization, can counteract this negative trend in temperate regions (Alvarez, 2005).

Nitrogen (N) is the main nutrient limiting crop growth in the Southern Pampas (Echeverría and Sainz Rozas, 2006a, Echeverría and Sainz Rozas, 2006b). As a result, crops respond to N fertilization, mainly by increasing above-ground and root biomass production (Tognetti et al., 2006). This increase leads to more crop residue returned to soil (Studdert and Echeverría, 2000) which, in temperate agro-ecosystems, is considered the main factor controlling total soil organic carbon (TOC) dynamics (Stevenson and Cole, 1999). In a review of published information about Typic Argiudolls, Alvarez (2005) demonstrated that from 20 medium-term experiments (under 10 years) involving N fertilization, 10 showed an increase and six a decrease in TOC compared to unfertilized plots, while four were unaffected (Reeder et al., 1998, Varvel, 1994, Fabrizzi et al., 2003). These disparate results are a result of the differences in the balance between the amount of residues returned to soil and their decomposition rate (Khan et al., 2007), and depend on many factors such as the cumulative N applied, rotation, climate and soil texture (Alvarez, 2005). So, the effects of N fertilization on the soil cannot be generalized and must be evaluated in each particular condition.

Also, other soil properties are highly related to TOC content and can therefore also be modified by N fertilizers. These are properties such as bulk density (BD) (Jagadamma et al., 2008), aggregate stability (AS) (Blair et al., 2006) and N mineralization potential (Kolberg et al., 1999, Carpenter-Boggs et al., 2000). Some fertilizers like urea can also reduce soil pH (Liebig et al., 2002, Franzluebbers and Hons, 1996), a process that can be limited by the application of lime (Caires et al., 2005).

Phosphorus (P) is another limiting nutrient for crop production in the Southern Pampas region, where the P Bray level in the soil surface ranges from 10 mg kg⁻¹ to 20 mg kg⁻¹ (Sainz Rozas et al., 2011). However, the effect of this nutrient on soil properties has never been studied in this area, or in soils with similar characteristics. In an experiment in a semi-arid area with P Bray values similar to those found in the Southern Pampas (13.4 mg kg⁻¹), but with lower TOC (50 Mg ha⁻¹ in 0–45 cm soil layer), Purakayastha et al. (2008) determined a 6.3% increase in the average annual root biomass yield generated by cumulative P fertilization. Although this caused an increase of 0.13 Mg ha⁻¹ year⁻¹ in the estimated C return, the TOC content was not altered. In the same area, Rudrappa et al. (2006) found a slight increase in C fractions between N and N + P treatments. As soils with high C content have a low C storage capacity (Hassink and Whitmore, 1997), we would expect this response to be lower on a Typic Argiudoll.

Although N and P deficiencies are widespread in the area, crops began to respond to nutrients that were not limiting before, for example sulphur (S) (Pagani et al., 2009) and some micronutrients (Sainz Rosas et al., 2003), due to soil degradation. Therefore, fertilization with these nutrients may increase the amount of crop residues returned to soil. However, it was found that S fertilization did not affect TOC in soils with low C content (Mandal et al., 2007, Masto et al., 2007), and there are no reports of its effect on high TOC soils.

Tillage systems also contributed to soil quality reduction in the Southern Pampas (Steinbach and Alvarez, 2005). Among them, conventional tillage (CT) comprises the use of moldboard plowing, disking and field cultivation, and acts aggressively on the soil. However, in the early 1990s no-till (NT) management practices were introduced, and by 2009 this method was used on more than 75% of the Pampas planted area (AAPRESID, 2011). The introduction of NT management leads to changes in soil properties, such as TOC content (Puget and Lal, 2005), AS, BD (Alvarez and Steinbach, 2009), potentially mineralizable N (Fabrizzi et al., 2003), pH and nutrients stratification (Franzluebbers and Hons, 1996). These changes could interact with those produced by fertilization, altering their effect on the soil. For example, Fabrizzi et al. (2003) determined that changes in the TOC caused by N fertilization are more pronounced in the first layer of soil using NT methods.

As soil properties have a direct effect on crop growth and development, variations in yield can be used to detect changes in the edaphic environment. Maize is a crop commonly planted in the area, and it has been found to be sensitive to the changes caused by tillage (Domínguez et al., 2009) and N fertilization (Jagadamma et al., 2008).

Understanding the combined effect of tillage practices and fertilization on soil and crops can help to develop strategies to restore soil quality in the Southern Pampas. To achieve this, information obtained from medium-term experiments is essential, because it not only allows for a comparative assessment between two or more contrasting situations (Larson and Pierce, 1994), but it also provides knowledge about the direction and magnitude of change being generated by a management practice (Wienhold and Halvorson, 1999).

The objective of this study was to determine the medium-term effects of N, P, S, micronutrients and lime application under two different tillage systems (CT and NT) on the physical, chemical and biological properties of a Typic Argiudoll and the response of maize to these changes in the Southern Pampas.

We hypothesized that: (1) medium-term N fertilization alters soil properties, and its effects depend on tillage systems; (2) medium-term fertilization with P, S and micronutrients, and liming do not affect soil properties; (3) maize crop is capable of detecting changes in soil properties caused by tillage and fertilization.