Higher lime rates for greater nitrogen recovery: A long-term no-till experiment labeled with ¹⁵N

Highlights

• Soil fertility increases after long-term liming with higher lime rates.

• The ¹⁵N-fertilizer recovery by crops is proportional to the soil fertility level.

• Low lime rates increased the concentration of ¹⁵N-fertilizer in deep soil layers.

• The higher ¹⁵N recovery leads to higher yields and lower N-fertilizer losses.

Abstract

Context or problem

Soil acidity limits crop growth and yield all over the world. Low grain yields is usually associated with poor soil fertility; however, little attention has been given to the nitrogen-based fertilizer use efficiency in soils managed with lime.

Objective

Given the current scenario of uncertainties regarding the availability and prices of fertilizers, our study aimed to understand how maize intercropped with ruzigrass and soybean plants develop in long-term soils managed with lime rates, and what the fate of the ¹⁵N–labeled ammonium sulfate [(¹⁵NH₄)₂SO₄] applied in the soil-plant system.

Methods

The treatments consisted of four dolomitic lime rates applied to the soil surface [control, half the recommended lime rate (½ RLR), full recommended lime rate (1 RLR) and double the recommended lime rate (2 RLR)].

Results

The higher lime rate (2 RLR) improved fertility, carbon and nitrogen stocks in the soil profile, and grain and/or stover production of maize, ruzigrass and soybean. As a consequence, maize and ruzigrass recovered a high amount of ¹⁵N-fertilizer. On the other hand, soybean recovered less ¹⁵N-fertilizer, regardless of treatment, but a greater amount was found in acidic soils. At the end of the maize and soybean growth cycles, our results showed that in 2 RLR-amended soil, the ¹⁵N unrecovered was 71% lower than control. Finally, our results suggested that the use of low lime rates (½ RLR) may increase the ¹⁵N losses potential to deep layers, whereas low amounts of ¹⁵N were found in the subsoil when higher lime rates were applied.

Conclusions and implications

Soil acidity management through higher lime rates leads, over time, to increased soil fertility, resulting in a favorable environment for plant growth and the use of nitrogen fertilizers. In this way, it is possible to obtain a more productive and less costly agricultural system, and with less potential to pollute the environment.

Introduction

Lime application is an important practice for ameliorating soil acidity (Meng et al., 2019, Šiaudinis et al., 2020), a common issue in many tropical regions around the world (Li et al., 2019, Patra et al., 2021). Standard lime application practices have been developed for long-term conservation systems in which there is no soil disturbance, such as no-tillage systems (NTSs) (Tiritan et al., 2016, Carmeis Filho et al., 2017a, Bossolani et al., 2021b). In addition to correcting soil acidity, liming improves soil fertility by supplying calcium (Ca²⁺) and magnesium (Mg²⁺), reducing toxic aluminum (Al³⁺) levels, and increasing soil organic matter (SOM) content over time (Briedis et al., 2012, Bossolani et al., 2022a). As a consequence of soil improvements, the crop root system can growth to deep layers, leading to higher uptake of soil resources (water and nutrients) (Crusciol et al., 2019, Bossolani et al., 2021b, Bossolani et al., 2022a), and greater fertilizer use efficiency (Fageria and Nascente, 2014, Crusciol et al., 2022b).

For maize (Zea mays L) and soybean (Glycine max) crops, nitrogen (N) is the most important nutrient (Bender et al., 2013, Bender et al., 2015). Biological nitrogen fixation (BNF) provides practically all necessary N for soybean (Freitas et al., 2022). However, for maize, N fertilizers are required, which significantly impacts production costs (Lu et al., 2021), particularly in the current scenario of rising fertilizer prices (Schnitkey et al., 2022). Furthermore, the complex dynamics of N in the soil–plant system can cause losses by volatilization, denitrification and leaching of nitrate (NO₃^-) in the soil profile (Zhou et al., 2021). Interestingly, leaching accounts for the majority of N losses (Tamagno et al., 2022). Nevertheless, N-fertilizer not absorbed by crops and present in soil surface layers (biologically active layers), can be lost by denitrification (Bossolani et al., 2020a). Agricultural practices that improve soil chemical characteristics can favor crop root growth, thereby allowing the exploitation of a greater volume of soil and reducing NO₃^- leaching and denitrification (Caires et al., 2016).

In NTSs, soil chemical attributes at deeper soil layers can be improved by applying higher rates of lime on the soil surface (Carmeis Filho et al., 2017a, Bossolani et al., 2022a), which can be enhanced by including tropical forage grasses in the system, particularly intercropped with maize (Ceccon et al., 2013, Costa et al., 2021). Tropical forage grasses, such as ruzigrass, present abundant and aggressive root growth, occupying a large volume of soil (Baptistella et al., 2020). When decomposing, these roots form biopores in the soil (Rosolem et al., 2017), facilitating the translocation of suspended particles from the lime to deeper soil layers (Tiritan et al., 2016, Bossolani et al., 2020b). Under these conditions, a soil acidity correction front forms in deeper layers down to 1.0 m, favoring greater growth of the subsequent crop root system, and thus increasing the possibility of NO₃^- absorption (Calonego and Rosolem, 2010), and reducing their losses to the environment (Rosolem et al., 2017).

In the present study, we hypothesized that the surface application of double the recommended lime rate under long-term NTS based on maize intercropped with ruzigrass followed by soybean would: i) improve chemical attributes in the soil profile; ii) increase biomass production; iii) increase the recovery of ¹⁵N-fertilizer by maize, ruzigrass and soybean crops; and iv) reduce ¹⁵N loss by potential leaching. To test these hypotheses, we evaluated the effects of surface application of different lime rates in a long-term experiment on soil fertility down to a depth of 100 cm; soil C and N stocks; maize, ruzigrass and soybean aboveground biomass production; the recovery of ¹⁵N fertilizer by the crops; and the stratified soil ¹⁵N down to 100 cm depth.