Variabilidade espacial do intervalo hídrico ótimo de solos cultivados em sistema plantio direto

Abstract

Resumo -O objetivo deste trabalho foi avaliar a acurácia das regressões que definem os limites do intervalo hídrico ótimo e a validade do uso deste indicador ao se considerar a variabilidade espacial de lavouras sob sistema plantio direto. Foram coletadas 100 amostras de solo com estrutura preservada, em áreas com dimensões de 10x10 m, em Latossolo Vermelho distrófico, Nitossolo Vermelho distroférrico e Latossolo Vermelho aluminoférrico, manejados sob sistema plantio direto. Determinaram-se porosidade de aeração (0,10 m 3 m -3 ), capacidade de campo (potencial de -0,006 MPa), ponto de murcha permanente (potencial de -1,5 MPa) e resistência mecânica do solo à penetração crítica (2 MPa). As regressões que descreveram a capacidade de campo tiveram os menores coeficientes de determinação, enquanto as que descreveram a porosidade de aeração, o ponto de murcha permanente e a resistência mecânica do solo à penetração apresentaram os maiores valores. As regressões que definem o limite da capacidade de campo não são acuradas em descrever a variação na umidade volumétrica do solo por meio da densidade do solo, e os solos avaliados apresentam elevada variabilidade espacial para o intervalo hídrico ótimo.Termos para indexação: capacidade de campo, ponto de murcha permanente, porosidade de aeração, resistência mecânica do solo à penetração. Spatial variability of the least limiting water range of soils under a no-tillage systemAbstract -The objective of this work was to evaluate the regressions that define the least limiting water range limits and the validity of using this indicator considering the spatial variability of crops under a no-tillage system. One hundred undisturbed soil samples were collected in areas with dimensions of 10x10 m, in two different Oxisols and an Ultisol managed under no-tillage. Air-filled porosity (0.10 m 3 m -3), field capacity (potential of -0.006 MPa), permanent wilting point (potential of -1.5 MPa), and soil mechanical resistance (2 MPa) were determined. The regressions that described field capacity had the lowest coefficients of determination, whereas those that described air-filled porosity, permanent wilting point, and soil mechanical resistance to penetration showed the highest values. Regression adjustments that define field capacity limits are not accurate in explaining variation on volumetric soil water content through bulk density, and the evaluated soils show high spatial variability regarding the least limiting water range.

Least limiting water range in Oxisol under two conservation tillage systems in sugarcane farming

“…Dias et al (2016), working with sugarcane, finding that these typical results due to high soil bulk density or compacted soils, relating to high water content so that the PR does not reach the limiting value. Several authors also observed that the influence of SW RP to the LLWR of soil in different soil management systems (Leão et al, 2004;Moreira et al, 2014;Silva et al, 2017;Fashi et al, 2017) and texture classes (Pereira et al, 2015;Dias et al, 2016;Klein et al, 2016).…”

“…Critical value selection of the PR interferes with the range of the LLWR and the value of the critical soil bulk density -SCD (Moreira et al, 2014). Klein et al (2016) state that the use of the value of 2.0 MPa as restrictive under no-tillage appears to be inadequate, once crops seek ways for lower restriction for their growth cycle, thus, under these systems largest values of PR are commonly observed. Several authors studying the LLWR consider that a different critical PR of 2.0 MPa (Tormena et al, 1998;Betioli Junior et al, 2012;Araújo et al, 2013;Moreira et al, 2014).…”

“…According to Figure 3 and 4, the adoption of a restrictive value of the PR to the crop growth has a direct consequence on the LLWR, demonstrating that such values must be very well studied in order to be more reliable when taking decision on the best management of soil in the sugar cane cultivation (Klein et al, 2016).…”

“…The LLWR is used as soil physical and structural quality indicator defining the interval between the upper and lower limits of water content in the soil, which are minimal limitations for plant growth caused by unavailability water, aeration deficiency and soil resistance to penetration (Fashi et al, 2017). With the increase of the soil bulk density, generally, the value of the LLWR decreases, being able to reach the null value, which corresponds to the critical or restrictive soil bulk density, when upper and lower limits are numerically equal (Klein et al, 2016). Klein et al (2016) reported that LLWR, besides of depending on the soil type, assumes different ranges depending on the soil bulk density, water soil retention curve and aeration and porosity.…”

“…With the increase of the soil bulk density, generally, the value of the LLWR decreases, being able to reach the null value, which corresponds to the critical or restrictive soil bulk density, when upper and lower limits are numerically equal (Klein et al, 2016). Klein et al (2016) reported that LLWR, besides of depending on the soil type, assumes different ranges depending on the soil bulk density, water soil retention curve and aeration and porosity. Additionally, the choice of the restrictive value of soil resistance to penetration (PR) to plant growth directly interferes to LLWR values and critical soil bulk density (Gubiani et al, 2013).…”