The modification of surface soil structure affects soil-water processes important in crop production and soil conservation. Effects of pretillage soil water content (PTSW) with multiple-pass tillage operations were determined on soil hydraulic properties and shortwave albedo on freshly tilled soil. Objectives included determination of whether PTSW can be used to improve management of seedbed hydraulic properties and whether tillage-induced soil surface conditions significantly affect albedo. Of the three tillage sequences (minimum, intermediate, and excess tillage) applied to a Templeton silt loam soil (mixed, mesic Udic Ustochrept), the excess tillage sequence resulted in the lowest macropore volume, mainly through a decrease in the volume of aeration pores (pores >300-ju.m diam.). The slope of the water characteristic between -1.0 and -1500 kPa matric potential was unaffected by tillage treatments. The excess tillage sequence resulted in a mean hydraulic conductivity (matric potential = -0.4 kPa ) of 11.1 cm h~', compared with 14.9 cm h~' following minimum tillage. Different PTSW did not cause significant differences in hydraulic properties of freshly tilled soil. The range of tillage-induced soil structures produced did affect shortwave albedo, but to a smaller extent than shown in some previous studies. Bare soil shortwave albedo variation with zenith angle appears soil specific; here a small decrease in albedo was observed as zenith angle increased. In this soil, with commonly practiced tillage sequences and a range of PTSW representative of field conditions, information about PTSW will not help manipulation of hydraulic properties and shortwave albedo in the fresh seedbed.
Over recent years regulatory authorities in New Zealand have promoted
irrigation of dairy farm effluent (DFE) onto the land, to protect surface
water quality. The rate at which the resistant organic matter from DFE
accumulates in the soil and the effect of any accumulation on other soil
organic matter (SOM) related pools, such as microbial biomass, are, however,
unknown. This information is necessary to determine the long-term impact and
sustainability of land-applied DFE.
In this paper we report on changes over 4 years in organic carbon (C
org) and total nitrogen (N t )
from a soil receiving a high application rate of DFE. Soil microbial biomass
(C mic ) measurements were also included to test the hypothesis that C
mic or the C mic /C
org ratio can be used as an early indicator of changes
in SOM.
The regular irrigation with DFE at the high rates used in this study increased
the C mic , pH, C org , and N
t of the soil receiving the effluent. The time series of
C mic showed that this measurement is suitable as an
early indicator of changes in C org and N
t , whereas a single determination of the C
mic /C org ratio was not.
The sustainability of DFE application onto land in terms of N leaching can be
maintained only when the supply of inorganic N is continually matched by the
demand of the pasture. This means that inorganic N fertilisation has to be
reduced concurrently with the gradually increasing N mineralisation from the
accumulating organic matter.
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