Soil Quality for Crop Production and Ecosystem Health
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Martins et al. Thus, these authors concluded that aggregation is indirectly affected by the input of plant pentose through the input of above-ground biomass. Such favorable effects may even be observed in the first years because of the absence of soil disturbance and reduction in machine traffic Tormena et al. A decrease in critical bulk density by root growth depends on the soil texture, mineralogy, particle shape, and soil organic matter content, which affect water and air movement and soil resistance to penetration Reichert et al.
Soil structural quality may be assessed by determining a balance in fluid air vs water transmission, water storage, nutrients in the soil solution, and air-filled porosity Topp et al. A favorable level of these attributes is important for improving crop growth, while reducing the risk of accelerated erosion and promoting root growth Reynolds et al. The range of soil properties which improve plant growth depends on strong interaction among soil resistance to penetration, air-filled porosity, and available water capacity, which is obtained from the difference between field capacity and the permanent wilting point Tormena et al.
What is known as the least limiting water range Letey, ; Silva et al. Thus, the least limiting water range is an important indicator of soil structural quality in relation to crop yield Silva et al. Therefore, it is important to evaluate the effects of plants on soil structural properties within specific cropping sequences, and to understand which and how soil attributes may be affected by specific crops. Thus, the present study was carried out to test the hypothesis that cropping sequences affect soil structural properties.
The objective of the study was to evaluate the effects of cropping sequences under no-till on soil structure and soil organic C sequestration. Rainfall is greater from October to March, with a relatively dry season from April to September. Details of some meteorological characteristics of the experimental site are shown in figure 1.
Particle size distribution in the Other mineralogical properties are detailed by Martins et al. The site history, soil chemical properties, lime applications, row spacing, and final plant populations of this experiment have been provided by Marcelo et al. The experiment was laid out according to a split-block design with three replications blocks. Each experimental block was composed of 21 plots, which consisted of three summer cropping sequences combined with seven winter crops in a no-till system.
Each plot was 40 m long and 15 m wide. Winter crops consisted of corn, sunflower Helianthus annuus L. The same winter crop was grown in the same plot during each growing season. A total of 20 subsamples were obtained from the In addition, at the same depth, 28 undisturbed core samples were also obtained from each plot.
Soil samples were placed within plastic bags to preserve structure and the moisture content during transport to the laboratory. The composite disturbed samples were broken up manually at field moisture content and divided into three portions. The first portion was sieved to obtain soil aggregates from 6. The air dried soil aggregates of the 4.
Plant Production and Protection Division: Agriculture and soil biodiversity
Three replicates of aggregates of 40 g and one of 10 g were weighed. The other three samples were used for wet sieving by using a nest of five sieves: 4.
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After the aggregates in the top sieve 4. Samples were subjected to wet sieving for 15 min at 31 cycles min -1 and a mm amplitude. Soil aggregates of 1. Four replicates of 10 g of 1. The other three replicates were used to determine water stable aggregates by using a sieve of 0. After the aggregates were wetted by capillarity, the sieve was oscillated under water for 3 min at 35 cycles min -1 , with an oscillation amplitude of 13 mm Yoder, To quantify the sand fraction, the oven-dried soil in the aluminum capsules was dispersed by adding mL of 0.
The suspension was passed through the same nest of sieves that retained aggregates during the wet sieving procedure 0. Soil organic carbon was transformed to the equivalent soil layer Bayer et al. The SOC content under a native forest Considering the soil organic matter content of Yield of crop residue was evaluated at two different times.
The first evaluation involved only quantification of the above-ground biomass and it occurred when the crops oilseed radish, pearl millet, pigeon pea, and sunn hemp were at the full bloom and when grain crops corn, sunflower, grain sorghum, and soybean were at the harvest stage. The above ground biomass was assessed by harvesting a one - meter-long row at three randomly selected locations in each plot, and the harvest was combined. The second evaluation was done to quantify the crop residue left on the soil surface after they were cropped cover crops or harvested grain crops.
All residues remaining on soil surface contained within a quadrat of 0. The least limiting water range was determined according to the method of Silva et al. Critical values for plant growth were obtained from the literature, i.
Evaluating long-term impact of land use on selected soil physical quality indicators
The least limiting water range was determined as the average of three replications for each matric potential. Thus, seven undisturbed soil cores were collected from each plot six cores of 0. These cores were separated into seven groups with 63 cores and were wetted by capillarity.
Each group was subjected to water suctions of 60 and hPa on a Tension Table Romano et al. The group with the smallest cores 0. Resistance to penetration was evaluated in each core at every matric potential using a penetrometer equipped with a linear actuator and load cell of 20 kg, operated at a constant speed of 1. These data were used to calculate the least limiting water range Silva et al. The degree of flocculation was obtained by:.
The data were subjected to analysis of variance according to a split-block design with three replications blocks , except for the least limiting water range. As soybean is a legume, the N fixed by it may be used by the following winter crop to produce the above-ground biomass. This high biomass yield was attributed to high availability of soil N introduced by biological fixation and the high potential of these cereal crops with an adequate supply of N Marcelo et al.
In a study to assess N uptake capacity and its effect on the biomass yield of corn in response to the addition of sunn hemp and pearl millet residues in an Oxisol, Silva et al. An increase in biomass yield through the use of legume residues may enhance SOC content in the soil and improve the grain yield of cereal crops Amado et al. Among the winter crops, pigeon pea and pearl millet produced higher above-ground biomass than corn, sunflower, oilseed radish, and sunn hemp Table 1.
This trend may be due to the drought and cold tolerance of these species in regions with a dry winter. Pearl millet is used as a winter crop in dry tropical climates because of its fast growth and high biomass yield Pacheco et al. Pigeon pea is also a suitable species for producing a high biomass yield with a low rate of decomposition because of a lower polysaccharide and a higher aromatic compound content. Thus, pigeon pea residues have higher aromaticity and hydrophobicity Carvalho et al.
Marcelo et al. These trends were attributed to the adaptability of these winter crops to the Cerrado region of Brazil. There were no differences in crop residues on the soil surface among summer crops Table 1.
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Nonetheless, among winter crops, pigeon pea had the highest quantity of residue on the soil surface. Plots under pigeon pea also had the highest quantity of above-ground biomass contributing to residues on the soil surface.
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Alvarenga et al. The higher residue from pigeon peas was partly attributed to its greater root length and diameter with high penetration potential in the subsoil, which enhances water uptake from deeper soil layers Alvarenga et. Furthermore, the corn root system is more relevant for improving the SOC stock than the addition of above-ground residues to the soil surface because the C in the root biomass is better stabilized into aggregates in the soil profile Santos et al. Residues on the soil surface protect soil aggregates against the degradation of SOC by microorganisms Sollins et al.
This hypothesis was also confirmed for the same site by Martins et al. The SOC stock did not differ among the winter crops Table 1. Nonetheless, the SOC content was higher in soil under grain sorghum and sunn hemp than soil under sunflower. Grain sorghum and sunn hemp have deep and prolific root systems with a high capacity of development in the soil profile, which increases SOC in the subsoil Marcelo et al.
Among the winter crops, grain sorghum and sunn hemp led to higher rates of SOC sequestration than sunflower Figure 2. In addition, the A high rate of SOC sequestration may be attributed to the winter crop established before the dry season. The water dispersed clay and degree of flocculation were significantly affected only by the summer crops Table 1.
The SOC content may be strongly correlated with water dispersed clay, indicating the importance of SOC on clay stabilization Beutler et al. Growing corn as a summer crop continuously or in rotation increased the mean weight diameter and the geometric mean diameter of the soil compared to soybean Table 2.