tilled situations yet this effect was limited to the surface soil layer
(Table 2). Increasing fertilizer N rates reduced the K stocks in the soil
yet this response differed by soil depth, with K levels showing a linear
decrease with increasing N rate in the surface soil but a curvilinear response
in the deeper layer (Fig. 3).
3.5. Soil pH and EC
Soil pH was not affected by residue removal or tillage practices or
their combination treatments (Tables 1 and 3) yet it was statistically
and negatively affected by increasing fertilizer N rates in the surface
soil layer. The statistically significant N rate interaction with depth
(Nr × D) indicated that the negative linear response to Nrate did not extend
to the deeper soil layer (Table 1). Partial or full residue removal
rates lowered the EC in the surface soil compared to the EC under no
residue removal, but did not affect EC within the deeper soil layer. On
the other hand, EC values showed no response to N rate in the surface
soil, but a negative (concave) quadratic trend in the deeper soil layer
(data not shown). The statistically significant interaction effect of tillage
and depth of sampling (significant T × D) found for EC (Table 1) reflects
higher EC in the surface soil compared to the deeper layer yet the magnitudes
are similar between tillage options at both depths studied
(Table 3).
4. Discussion
While maize crop residues are an important potential source of biomass,
their removal also means some loss of nutrients for the soil, and
thismight negatively affect SOC, fertility and long termproductivity, regardless
of the soil type and ecosystem. The response of soil to residue
removal is assumed to be site-dependent, and a number of reports
tilled situations yet this effect was limited to the surface soil layer(Table 2). Increasing fertilizer N rates reduced the K stocks in the soilyet this response differed by soil depth, with K levels showing a lineardecrease with increasing N rate in the surface soil but a curvilinear responsein the deeper layer (Fig. 3).3.5. Soil pH and ECSoil pH was not affected by residue removal or tillage practices ortheir combination treatments (Tables 1 and 3) yet it was statisticallyand negatively affected by increasing fertilizer N rates in the surfacesoil layer. The statistically significant N rate interaction with depth(Nr × D) indicated that the negative linear response to Nrate did not extendto the deeper soil layer (Table 1). Partial or full residue removalrates lowered the EC in the surface soil compared to the EC under noresidue removal, but did not affect EC within the deeper soil layer. Onthe other hand, EC values showed no response to N rate in the surfacesoil, but a negative (concave) quadratic trend in the deeper soil layer(data not shown). The statistically significant interaction effect of tillageand depth of sampling (significant T × D) found for EC (Table 1) reflectshigher EC in the surface soil compared to the deeper layer yet the magnitudesare similar between tillage options at both depths studied(Table 3).4. DiscussionWhile maize crop residues are an important potential source of biomass,their removal also means some loss of nutrients for the soil, andthismight negatively affect SOC, fertility and long termproductivity, regardlessof the soil type and ecosystem. The response of soil to residueremoval is assumed to be site-dependent, and a number of reports
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