Critical limits of the degree of compactness and soil penetration resistance for the soybean crop in N Brazil

Abstract

In agricultural fields soil compaction is a major cause of physical degradation. Degree of compactness (DC) is a useful parameter for characterizing compaction and the response of crops for different soils. The objectives of this study were: (1) to identify the critical DC and PR values for soybean [Glycine max (L.) Merrill] using plant growth variables and (2) to verify the relationship between DC and PR, and assess which parameter is recommended for the evaluation of soil compaction. The study was conducted in a greenhouse in a completely randomized factorial design of 4 textures × 5 compaction levels for sandy loam and sandy clay loam soils, and 3 compaction levels for the clayey and very clayey soils. Soil samples were collected from the surface of a Xantic Kandiudox from the NE region of the State of Pará, Brazil. The DC was calculated from the maximum bulk density obtained by the Proctor test, and the PR curve was determined in undisturbed samples equilibrated in different matric potentials. The growth and development of the soybean was favored in the DC range of 80 to 85%, regardless of soil texture. The critical degree of compactness for the growth of soybean was around 98% regardless of soil texture, while the critical values for penetration resistance at field capacity varied according to soil texture and bulk density and were 28.2, 5.6, 3.5, and 5.2 MPa for the sandy loam, sand clay loam, clayey and very clayey soils, respectively. The root length was the plant growth variable most susceptible to soil compaction. Change in soil penetration resistance was poorly related with change in degree of compactness showing that one parameter cannot be replaced by the other. Because PR is quickly determined in field and have a direct relationship with plant growth, for the soils evaluated in this study we recommend the use of soil PR to assess the state of soil compaction.

Tráfego de máquinas agrícolas em cultivo de palma de óleo

“…Estudos têm sugerido valores de GC ótimos e críticos para o desenvolvimento das culturas, no entanto, a maioria dos estudos avaliaram culturas anuais, tais como a soja (Oliveira et al, 2016). Com base nos valores de GC sugeridos na literatura (77-90 %) os resultados evidenciam que há limitações físicas para o crescimento e desenvolvimento normal das plantas na área avaliada, na profundidade de 0-40 cm.…”

“…O grau de compactação nas duas profundidades foi comparado pelo teste t (p < 0,05), utilizando o programa estatístico R (R Development Core Team, 2011). As variáveis Ds max e θ C são influenciadas pelo conteúdo de argila e matéria orgânica (MO) no solo (Oliveira et al, 2016). Porém, apesar do aumento de quase 10% no conteúdo de argila da camada de 0-20 para a de 20-40 cm, os valores de densidade do solo máxima (Ds máx ) e umidade crítica para compactação (θ C ) pouco variaram entre as duas profundidades.…”

“…Na avaliação dos impactos do uso e manejo na qualidade física do solo, o grau de compactação (GC) é utilizado para determinar a susceptibilidade de um solo à compactação, obtida pelo teste de Proctor (Håkansson, 1990;Oliveira et al, 2016). Além do GC, a resistência à penetração (RP) também é um atributo indicado para a avaliação da condição física do solo, devido sua relação direta com o crescimento das plantas (Suzuki et al, 2013).…”

Critical soil bulk density for soybean growth in Oxisols

“…Subsamples were used for fertility analysis according to procedures described by Embrapa (2011). The fertility analysis (Oliveira et al, 2015) showed that the soil was limed and fertilized according to the soybean crop requirements (Embrapa, 2010).…”

“…After the addition of each layer, the soil surface was slightly scratched for addition of the next layer in order to improve contact and prevent the formation of distinct layers. Additional details about the soil compaction methodology in the pots are provided by Oliveira et al (2015).…”