Accuracy of the neutron probe for measuring changes in soil water storage under potatoes

2002 ◽  
Vol 138 (2) ◽  
pp. 135-152 ◽  
Author(s):  
S. R. GAZE ◽  
M. A. STALHAM ◽  
E. J. ALLEN
Keyword(s):  
Field Experiment ◽  
Soil Water ◽  
Water Storage ◽  
Surface Profile ◽  
Soil Surface ◽  
Bare Soil ◽  
Irrigation Scheduling ◽  
Soil Water Storage ◽  
Neutron Probe ◽  
Areal Sampling

The neutron probe (NP) is used widely to measure changes in soil water storage in research and more recently to aid irrigation scheduling. Its accuracy is rarely questioned and most of the relationships between soil water changes and productivity are based on its use. A field experiment was conducted at Cambridge University Farm in 1999 to address whether the NP could accurately measure changes in soil water content (SWC) under irrigation or substantial rain (>10 mm). The experiment was a replicated split-plot design with four irrigation treatments allocated to the main plots, and surface profile (ridge, flat) and crop (potato cv. Saturna, bare soil) treatments allocated to the subplots. The mean results from four NP access tubes per plot installed to measure soil moisture deficit (SMD) across the row-width were analysed. The NP was inconsistent in measuring known irrigation or rainfall input. In relatively dry soil (SMD>40 mm), the NP generally measured 93 to 110% of 18 mm of irrigation within 4 h of irrigation. The NP recorded much less water applied as irrigation in wetter soil, and often only 40 to 70% of the applied irrigation (18 or 36 mm) was measured. There were occasions when the NP did not measure all the water input even when the SMDs before irrigation were greater than the water subsequently applied. Some of the ‘missing’ water might be attributed to drainage, however, results from an additional experiment using an open-topped tank of soil showed that the NP was unable to detect all the water added to the soil, particularly where the water was largely confined close to the soil surface. Replicated measurements of the change in SMD in the field experiment were precise for a given event and treatment (mean S.E. = 1·3 mm) but were not accurate when compared against the input measured in rain gauges. It was concluded, that the NP could not be used reliably to measure changes in soil water storage after irrigation or substantial rain. For periods when there were minimal inputs of water, there was a closer correlation between changes in SMD measured by the NP and those predicted by a modified Penman–Monteith equation than after substantial inputs of water. However, for predicted changes in SMD of c. 20 mm, there was a range of c. ±5 mm in the changes in SMD measured by the neutron probe.The value of the NP for monitoring SMDs where there is irrigation, or substantial rain, must be seriously doubted. Consequently, its limitations for scheduling irrigation, testing models or quantifying the effects of treatments on crop water use in potatoes must be appreciated, especially where the areal sampling limitations of single access tubes positioned only in the ridge centre have not been addressed.

Soil water storage in a semi-arid Eucalyptus populnea woodland invaded by woody shrubs, and the effects of shrub clearing and tree ringbarking.

1984 ◽  
Vol 6 (2) ◽  
pp. 75 ◽  
Author(s):  
GG Johns
Keyword(s):  
Soil Water ◽  
Water Storage ◽  
Soil Surface ◽  
Bare Soil ◽  
Arid Environment ◽  
Soil Water Storage ◽  
Water Response ◽  
Shrub Clearing ◽  
Eucalyptus Populnea ◽  
Semi Arid

Soil water was monitored over a six year period in an intact shrub invaded semi-arid Elrcalyptlts popztlrlea woodland (control) and on areas which had been treated by either shrub-clearing, or by ringbarking of trees and shrub-clearing. Measurements were made under both the shrubby thicket areas near the eucalypt, and the sparsely shrubbed interthicket areas more distant from the trees. Average soil water storage over the six years for all treatments was only 26 nun. Much of this water was stored in the upper 500 Inm of the profile and hence was susceptible to direct evaporation from the usually bare soil surface. In the intact n.oodland and following wet weather, significantly more soil water was stored under thickets than under the interthicket areas. With the return of dry weather this cxtra soil water was rapidly depleted, and thicket soils would often become drier than interthicket soils. After pro- longed dry weather, soil matric potentials of - 10 to -1 2 MPa were recorded at a depth of 500 mm. Matric potentials by this time were least negative under thickets. Shrub clearing without rinpbarking increased thicket and interthicket soil water storage by 17% and 2396 respectively. The ring- barking and shrub clearing treatment increased thicket profile storage more than that of the interthicket (81% and 64% respectively). The effect of ringbarkinp lvas often pronounced at a distance of 25 rn from the tree. The contrasting soil water response to the two treatments indicated that in this semi-arid environment only a relatively srnaU change in soil water balance may accrue from incomplete clearing. The ren~oval of both shrubs and trees is probably necessary to make a large difference to soil water storage.

scholarly journals Spatial variability and temporal stability of water storage in a cultivated tropical soil

Bragantia ◽  
2010 ◽  
Vol 69 (suppl) ◽  
pp. 153-162 ◽  
Author(s):  
Antonio Carlos Andrade Gonçalves ◽  
Marcos Antonio Trintinalha ◽  
Marcos Vinicius Folegatti ◽  
Roberto Rezende ◽  
Cássio Antonio Tormena
Keyword(s):  
Water Content ◽  
Soil Water ◽  
High Efficiency ◽  
Temporal Stability ◽  
Water Storage ◽  
Soil Surface ◽  
Soil Water Storage ◽  
Soil Conditions ◽  
Content Uniformity ◽  
Water Application

Irrigated agricultural fields usually show variable crop water demand. If water application is done to match this spatially variable demand, the water use efficiency can be substantially improved. Soil water management by irrigation has been one of the most important factors to increase crop yield. To look for the economic viability of the process, the use of several inputs, particularly water, should be done with high efficiency levels. Historically, irrigation uniformity has been evaluated above the soil surface, in which applied water was the only factor to be taken into account. However, the crop will respond to soil water content uniformity, which can differ from the uniformity of water application. To evaluate temporal stability of spatial pattern of soil water storage (SWS), this work was done on a Brazilian clayed soil. Volumetric water content from soil surface to 0,30m depth, was measured by TDR in 80 points regularly spaced (3 x 3 m) on an experimental area cultivated with bean crop, irrigated by conventional sprinkling. The evaluations were done immediately before and after a water application by irrigation. Experimental semivariograms made from values obtained in the field showed that SWS distribution was spatially structured and strongly stable in time, being regulated mainly by intrinsic factors of the soil. In addition, obtained results showed that water application uniformity did not influence the spatial distribution pattern of SWS in these soil conditions.

scholarly journals Water storage change estimation from in situ shrinkage measurements of clay soils

2012 ◽  
Vol 9 (11) ◽  
pp. 13117-13154 ◽  
Author(s):  
B. te Brake ◽  
M. J. van der Ploeg ◽  
G. H. de Rooij
Keyword(s):  
Soil Water ◽  
Water Storage ◽  
Soil Surface ◽  
Surface Elevation ◽  
Measurement Scale ◽  
Soil Water Storage ◽  
Soil Layers ◽  
Shrinkage Curve ◽  
Elevation Changes ◽  
Storage Change

Abstract. Water storage in the unsaturated zone is a major determinant of the hydrological behaviour of the soil, but methods to quantify soil water storage are limited. The objective of this study is to assess the applicability of clay soil surface elevation change measurements to estimate soil water storage changes. We measured moisture contents in soil aggregates by EC-5 sensors, and in volumes comprising multiple aggregates and intra-aggregates spaces by CS616 sensors. In a prolonged drying period, aggregate-scale storage change measurements revealed normal shrinkage for layers ≥ 30 cm depth, indicating volume loss equalled water loss. Shrinkage in a soil volume including multiple aggregates and voids was slightly less than normal, due to soil moisture variations in the profile and delayed drying of deeper soil layers upon lowering of the groundwater level. This resulted in shrinkage curve slopes of 0.89, 0.90 and 0.79 for the layers 0–60, 0–100 and 0–150 cm. Under a dynamic drying and wetting regime, shrinkage curve slopes ranged from 0.29 to 0.69 (EC-5) and 0.27 to 0.51 (CS616). Alternation of shrinkage and incomplete swelling resulted in an underestimation of volume change relatively to water storage change, due to hysteresis between swelling and shrinkage. Since the slope of the shrinkage relation depends on the drying regime, measurement scale and combined effect of different soil layers, shrinkage curves from laboratory tests on clay aggregates require suitable modifications for application to soil profiles. Then, the linear portion of the curve can help soil water storage estimation from soil surface elevation changes. These elevation changes might be measurable over larger extents by remote sensing.

FIELD SCALE PATTERNS OF SOIL WATER STORAGE FROM NON-CONTACTING MEASUREMENTS OF BULK ELECTRICAL CONDUCTIVITY

1990 ◽  
Vol 70 (3) ◽  
pp. 537-542 ◽  
Author(s):  
R. G. KACHANOSKI ◽  
I. J. VAN WESENBEECK ◽  
E. De JONG
Keyword(s):  
Electrical Conductivity ◽  
Soil Water ◽  
Electromagnetic Induction ◽  
Water Storage ◽  
Soil Water Storage ◽  
Fast Method ◽  
Field Patterns ◽  
Neutron Probe ◽  
Bulk Electrical Conductivity ◽  
General Field

Soil water storage (0–1.7 m) was measured every 10 m in a 660-m-long transect using a neutron probe and compared to bulk electrical conductivity, ECA, measurements obtained using noncontacting electomagnetic induction meters. Coherency analysis indicated a lack of correlation at scales less than 40 m. At scales greater than 40 m, ECA explained more than 80% of the variation of soil water storage. Measurement of ECA should be a simple and fast method of determining general field patterns of soil water storage. Key words: Spatial variability, soil water, coherency, electromagnetic induction

Lucerne in crop rotations on the Riverine Plains. 3. Model evaluation and simulation analyses

2007 ◽  
Vol 58 (12) ◽  
pp. 1129 ◽  
Author(s):  
K. Verburg ◽  
W. J. Bond ◽  
J. R. Hirth ◽  
A. M. Ridley
Keyword(s):  
Field Experiment ◽  
Soil Water ◽  
Root Zone ◽  
Water Storage ◽  
Crop Rotations ◽  
Soil Water Storage ◽  
Annual Rainfall ◽  
Large Variability ◽  
The Creation ◽  
Storage Buffer

The use of a lucerne phase in crop rotations can reduce water lost as drainage past the root zone under dryland agriculture in southern Australia. During the lucerne phase the perenniality of lucerne and its deep rooting ability allow extraction of soil water from below the root zone of annual crops and the creation of a soil water storage buffer against deep water loss. The longevity of the soil water storage buffer depends on rainfall patterns, management of the crops and summer fallows, as well as the magnitude of the buffer created during the lucerne phase. Results from a previously reported field experiment in north-eastern Victoria (average annual rainfall 600 mm) suggested that a 2-year lucerne phase could be insufficient to prevent drainage under subsequent crops for more than 1 year. Computer simulations were used to explore the implications of climatic variability on the creation and refilling of the soil water storage buffer. After first testing that the simulations described the experimental data satisfactorily, they were then used to extend the results and conclusions of the field experiment. These showed that the outcome of the experimental evaluation was affected by the climatic conditions experienced during the experiment and that a lucerne phase duration of 2 years was not appreciably less effective than a 3-year lucerne phase in reducing drainage past 1.8 m (the depth evaluated in the experiment). This conclusion was, however, sensitive to the depth at which drainage was evaluated and also depended on management factors such as the timing of lucerne removal and weed control during the summer fallows. For example, when drainage was evaluated to the maximum depth of lucerne rooting (3.6 m), lucerne was removed in December rather than April, and weeds were permitted, a third year of lucerne allowed a longer cropping phase without refilling of the profile in 47% of years. As a general recommendation a 3-year lucerne phase might, therefore, be an appropriate option for maximising the prevention of drainage. The large variability in the longevity of the soil water storage buffer (from 3 to > 45 months) and its sensitivity to management suggest, however, that it may be more beneficial to link phase changes to local assessment of the status of soil water storage buffer.

Hydrological processes and herbage production in shrub invaded Poplar Box (Eucalyptus populnea) woodlands.

1981 ◽  
Vol 3 (1) ◽  
pp. 45 ◽  
Author(s):  
GG Johns
Keyword(s):  
Soil Water ◽  
Water Storage ◽  
Free Water ◽  
Bare Soil ◽  
Hydrological Processes ◽  
Soil Water Storage ◽  
Water Losses ◽  
Run Off ◽  
Annual Distribution ◽  
Trees And Shrubs

The hydrological processes of relevance to herbage production in shrub invaded semi-arid popla box (Eucalvptus popuhea) woodlands are reviewed. Climatic limitations to herbage production in the poplar box lands are discussed in relation to the annual distribution of rainfall and evaporation. The limiting effects of trees and shrubs on herbage production within a woodland are then evaluated using data from a study site near Coolabah in north-western New South Wales. Hydrologic measurements made at the site include soil water storage, run-off and infiltration rates. Marked spatial variability in infiltration of water into the soil was in part related to the distribution of plants and redistribu- tion of water from ridges to adjacent flats occurred because of low rates of infiltration into bare soil areas between groups of trees and shrubs. From measurements of the depletion of soil water which accumulated during an exceptionally wet period the potential rate of evapotranspiration from the poplar box component of the woodland was estimated to be 0.5 times that from a free water surface. Bare soil evaporation accounted for approximately one half of water losses. Herbage production is shown to be poorly related to soil water storage alone, but the regression between herbage production and the product of water and nitrogen availabilities accounts for 70% of the vari~ce. It is concluded that the role of trees and shrubs in competing with herbage for nutrients, as well as water, is in need of clarification.

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