Eric Scopel

Resistência à penetração de um Latossolo Vermelho Amarelo do Cerrado sob diferentes sistemas de manejo

The intensification of agricultural production systems has caused soil compaction even when soil conservation technologies are adopted. Soil compaction is one of the main problems for farmers, both in no-tillage and in conventional-tillage systems, as well as in pasture. This study was conducted in Rio Verde, (State of Goias), on Red-Yellow Latosol under the following systems: no-tillage for 14 years (SD14); no-tillage for 8 years (SD8); no-tillage for 2 years (SD2); conventional tillage (CT); pasture (P) and forest (F). The soil resistance to penetration was measured by the impact penetrometer Model IAA/Planalsucar - Stolf, from soil surface to the soil depth of 0.40 m. Soil bulk density and granulometry were also determined. Conventional tillage had lower resistance to penetration at the 0-0.10 m depth, whereas SD2 had more resistance up to 0.40 m in depth. There were no significant differences below 0.15 m in depth among treatments CT, SD8, and SD14. The first two years under the no-tillage system are critical, with regard to the resistance to penetration in to the soil surface layers.

Long-term effects of continuous direct seeding mulch-based cropping systems on soil nitrogen supply in the Cerrado region of Brazil

In the Cerrado region of Brazil conventional soybean monoculture is since the 1980s being replaced by direct seeding mulch-based cropping (DMC) with two crops per year and absence of tillage practices. The objective of this study was to assess the long-term impact of DMC on soil organic matter accumulation and nitrogen (N) mineralization. Measurements of soil organic carbon (C) content, soil total N content and soil N mineralization, both under laboratory conditions using disturbed soil samples and under field conditions using intact soil cores were conducted on a chronosequence of 2-, 6-, 9- and 14-year-old DMC fields (DMC-2, DMC-6, DMC-9 and DMC-14, respectively). The average increase of organic C in the 0–30xa0cm topsoil layer under DMC was 1.91xa0Mg C ha−1 year−1. Soil total N increased with 103xa0kg N ha−1 year−1 (0–30xa0cm). The potential N mineralization rate under laboratory conditions (28°C, 75% of soil moisture at field capacity) was 0.27, 0.28, 0.39 and 0.36xa0mg N kg soil−1 day−1 for, respectively, the DMC-2, DMC-6, DMC-9 and DMC-14 soils. The corresponding specific N mineralization rates were 0.16, 0.15, 0.22 and 0.17xa0mg N g N−1 day−1. There was no obvious explanation for the higher specific N mineralization rate of soils under DMC-9, given the similar soil conditions and land-use history before DMC was introduced. Results from the in situ N incubation experiments were in good agreement with those from the laboratory incubations. We estimated that soil N mineralization increases with about 2.0xa0kg N ha−1 year−1 under DMC. The increase was mainly attributed to the larger soil total N content. These results indicate that even in the medium term (10xa0years), continuous DMC cropping has limited implications for N fertilization recommendations, since the extra soil N supply represents less than 20% of the common N fertilization dose for maize in the region.

Dinâmica da água nas palhadas de milho, milheto e soja utilizadas em plantio direto

The objective of this work was to evaluate the effects of crop residue mulches from maize, millet and soybean on water storage capacity, water evaporation, soil cover, solar radiation interception and surface water run-off as well as to incorporate these effects in a crop growth model. Thexa0mulch of millet and maize presented higher capacity for water storage than soybean mulch: 3.26, 3.24 and 2.62xa0g of water perxa0gram of dry matter, respectively. Water losses from wet mulches were related to the potential evapotranspiration. Thexa0soil cover levels were similar among the three types of material. Thexa0three types of mulch intercepted similar quantities of photosynthetically active radiation and infraredxa0radiation. Thexa0mulch of maize straw was slightly more efficient in intercepting radiation than that from millet or soybean. Mulching with millet residues was efficient in the control of surface water run-off: only 45.5xa0mm of water (out ofxa0843.5xa0mm rainfall) was lost through runoff under the no-till system with millet as cover crop, whereas 222.5xa0mm of water was lost in the conventional system with tillage. Most of the relations derived in this work could be described by exponential models.

The contribution of Stylosanthes guianensis to the nitrogen cycle in a low input legume-rice rotation under conservation agriculture

Background and aimsLegumes integrated in crop rotations are intended to improve crop nitrogen (N) supply and yield. In conservation agriculture (CA) systems under low input conditions on highly weathered tropical soils, experimental evidence for these benefits is lacking. To understand the mechanisms and evaluate the impact of the legume N on the subsequent crop, an in-depth study on N dynamics in the soil-plant system was conducted.MethodsIn Madagascar, a CA based crop rotation with the perennial forage legume Stylosanthes guianensis (stylo) and upland rice (rice/stylo – stylo - rice/stylo) was established under three fertilization regimes. In addition, rice was grown in a non-CA bare fallow rotation without fertilizer. Over the three years N2 fixed in stylo shoots, the incorporation of stylo shoot (mulch) N into soil N pools and mulch N uptake by rice was quantified using 15N techniques and mulch and stylo root residue decomposition was investigated in a litterbag study.ResultsN2 fixed in stylo shoots ranged from 96 to 122xa0kg N ha−1. Between 50 to 70% of stylo mulch and root residues decomposed during the third cropping season. Without fertilizer, grain yield of rice after the fallow with stylo was about 70% greater than after bare fallow, corresponding to 11xa0kg N ha−1 greater N uptake. Recoveries of stylo mulch N after rice harvest were on average 64% in soil, with about 3% in each of the microbial and mineral N pools, with 39% on the soil surface, and 6% in the rice crop. The N input via stylo seed, leaf litter and belowground N totalled about three times the amount of N contained in stylo mulch, which usually is considered as major rice N source.ConclusionsLegumes, like stylo, can improve crop N supply and yield in low input CA cropping systems on highly weathered tropical soils. To explain the impact and mechanisms involved requires a consideration of all legume-N components beyond the mulch N present at the onset of the rice-cropping season.