soil fertility and plant nutrition...
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EFFECTIVE PLACEMENT OF FERTILIZERSDr. JA Janse van Vuuren
Greenhouse Trial & Research Centrewww.greenhousetrials.co.za
Soil Fertility and Plant Nutrition Symposium“Effective Stewardship of Fertilizer in Practice”
21st August 2018, CSIR Convention Centre, Pretoria
Introduction
Variation in soil properties
Restraints of current soil sampling methodology
Sampling tools
Soil Doctor®
Real time soil sensors
Soil acidity the Australian experience
Prevention of detrimental effects of Spatial Variability
Different sampling methodologies
Field trial
Movement of lime in soils
Capacity and Intensity
Conclusions
References
Soil sampling for FAS is dependent on obtaining representative samples.
Fixed cultivation practices result in spatial variation in soil chemical properties.
Band placement of fertilizers being a major contributor.
Physical variation in row crops, on the row and away from the row, cause further heterogeneity in the soil.
If the nature and extent is not taken into account, averagesare obtained which have no resemblance to the chemical environment in the root zone.
Soil Variations are due to:
1. OVER FIELD VARIATION:
Natural (inherited) variation due the 5 soil forming factors:
Parent material, climate, topography, vegetation and time.
2. IN FIELD VARIATION:
Man-made variation due to management practices.
Row cropping, band placement of fertilizers, herbicides and other ameliorants.
This adds to the heterogeneity of chemical properties associated with soil fertility.
Despite the pivotal role of soil microorganisms in agro-ecosystems, we still have limited understanding of the complex response of the soil micro biota to organic and mineral fertilization in the very long term.
Soil is not material specific.
Soil properties are:
Extremely variable, not randomly distributed.
Systematic, time and space dependent.
The dilemma is that soil is not an isotropic medium, but rather strong an-isotropic, laterally and vertically.
Spatial variation in soil is a continuum from mega-to micro-scopic levels of resolution.
Soil scientists understand the kinetics of chemical reactions of a homogeneous soil sample.
Extrapolating the results to a larger more heterogeneous rhizosphere proves more challenging.
Similarly it is very difficult for microbiologists to account for changes in microbe-populations in the rhizosphere when the crop cover undergoes major changes.
It is not possible to model a system according to a typical response to cultivation practices without a sound understanding of spatial and time connected variation on a small and large scale.
Taking into account the number of samples taken annually and the heterogeneity of soils, it is clear that the intensity of sampling, even for precision agriculture, is inadequate.
Samples taken on the same GPS reference points:
Traditional Auger (7,5 cm diameter) – 15 cm deep.
Vehicle mounted probe (2.5cm diameter) 20 cm deep
RTSS-mounted tractor with cross-sectional view of the soil penetrator and probe housing.
Soil Acidity. A guide for WA farmers and consultants Chris Gazey, Stephen Davies & Ronald Master
Samples
Sampling between row
PREVENTION OF DETRIMENTAL EFFECTS OF SPATIAL VARIATION IN CHEMICAL PROPERTIES OF SOILS UNDER FIXED CULTIVATION PRACTICES.
Dr. JA Janse van Vuuren. PhD Thesis 1991, University of Pretoria, Department of Soil Science
Analysis variation over row
pH(H2O) 4,8 6,7 5,9
Average 5,9
Arbitrary Standard deviation – 2,2
Arbitrary Standard deviation – 2,2 mg/kg
Analysis variation over row
mg/kg lowest highest average
P (Bray 1) 16 115 28
Average –28 mg/kg
Multi –sampler used at end of season
Single sampler used at start of season
>6 5,9 – 5,6 5,5 – 5,1 5,0 – 4,6 4,5 – 4,0 FERTILIZER
BAND <4
288mm
684mm
AVERAGE36mm
>6 5,9 –5,6
5,5 –5,1
5,0 –4,6
4,5 –4,0
FERTILIZER
BAND <4
280mm
840mm
40mm
AVERAGE
Location: Farm Lusthoff District Lichtenburg, NW-Province. JPJ Kruger season 1988/89
Soil: Form – Avalon, Series Heidelberg, SaLm
pH(H2O) Top (0-15cm) 6,1; 19% Clay; Ca 498 mg/kg
pH(H2O) Sub (>30cm) 6,0; 27% Clay; Ca 558 mg/kg
Randomized block design with 4 replicates
Plot sizes - 20 x 9,12 meter (182,4m2)
Nett: 18 x 4,56 m (82,08m2) side rows discarded
Plant density 14, 133 plants/ha
Rainfall total for season 486mm
Mixed amorphic lime granules with the fertilizer in a 1:1 ratio at plant
kg/ha kg/ha Maize yield (kg/ha)
Fertilizer3:2:0 (25) + Zn
Lime granulesamorphous dolomite
Difference
Treatments 50 0 4661 b
50 50 5063 ab 402
100 0 4617 b
100 100 5288 a 671*
150 0 4888 ab
150 150 5424 a 536
Replicates 1 4855
2 5078
3 4998
4 5029
Average 4990
Co-efficient of variation 5,17
LSD (p=0,05) (TUKEY) Treatments 580
Means with the same letters do not differ significantly at the 5% significant level
8 Perspex rings, 90mm diameter, 2cm high, stacked onto each other to form a 16cm tube, taped together.
Tube filled with a un-buffered acid soil (pH <4(H20) up to 2nd last ring.
One gram of pelletized lime was spread on the soil surface.
Columns filled with water bringing the soil to field water capacity after free water drained from the tube.
The equivalent of 250mm of water/ha was added and left to dry.
Rings of column separated retaining soil in every ring.
Soil analyzed for Ca, Mg.
Procedure repeated to simulate 500 and 1000mm rainfall.
Procedure repeated using Ca(OH)2
The relative efficacy of different liming materials was tested in columns containing an acid un-buffered soil.
The different lime sources were banded in the center of the columns, at the equivalent of 10ton/ha.
Cation and Anion-root probes were placed 2cm below
the ameliorant bands in the soil at an angle.
Another set was placed 3cm below and perpendicular
to the top probes.
Probes were left in the soil the soil for 72 hours, removed, rinsed and analyzed.
Probes were replaced a further 3 times at 7 day intervals.
After placement the equivalent of 128mm of rain was applied and repeated after every placement. A total of 500mm equivalent water was applied.
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3days
10days
17 days
24days
31days
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CAPACITY FACTOR: is independent of:
Particle size distribution (Normally between 1,7mm - 1μ)
Physical form (granules, micronized powders or liquid limes)
Origin (Amorphous or crystalline)
One ton of a commercial lime (<1,7mm) same neutralizing capacity as 1ton of liquid lime (0,8μcentre cut)
INTENSITY FACTOR:
The smaller the particle size distribution of the product, the larger the surface area, the speedier neutralization of acid occurs, as efficacy remains a contact reaction.
Agricultural limes (carbonates) have very limited solubility in water.
Cold water 25°C - 0,00153grams/100cm3.
Hot water 75°C - 0,00190grams/100cm3.
Movement of calcium carbonate into the soil from surface application is time dependent.
Liming material applied on the top soil, reaction on the first2,5cm is almost immediately, up to 5cm is affected over a few months, and over years the pH changes even into the 7,5 -10 cm.
The problem however is that subsoil acidity occurs in the sub 15cm layers where it is difficult to ameliorate.
Normal broadcasting of agricultural liming materials essential –there is no substitute for correcting over field soil acidity –capacity factor.
Surface application of liming materials is not effective, has to be incorporated into the soil.
Liquid Lime – (0,8μcc) Very expensive, very specific application in fertilizer band. Only option with Hydro-seeding – intensity factor.
Liquid hydroxides also very expensive– at planting, if close to the seed, danger of burn and volatilization of Nitrogen
Granulation of micronized (40 μcc particle size). Main application as diluent for fertilizer at plant – increases efficacy of fertilizers on soils with low pH.
Reaction of w.s.-P applied in the fertilizer band precipitating with amorphic- Fe & Al hydroxide usually present in acid soils, are reduced.
Stimulation of beneficial soil micro-flora (bacteria & actinomyces) and microbial processes.
Efficacy of banded herbicides in these zones are probably increased.
Strong tendency to increases in yield.
No negative effects were observed in mixing lime with fertilizers in the research, it remains a safe option.
Crop Technology, Inc. Soil Doctor® Soil Sensing System, EM38, www.soildoctor.com; [email protected]
Franzen, D. Extention Soil Specialist. Growing problem of surface soil acidity in long-term no-till. June 10, 2018, Posted in soil health. North Dakota Stae University Extension.
Francioli, D, Shultz, E., Lentendu, G., Wubet, T., Buscot, F. & Reitz T. Mineral vs. organic Amendments: Microbial community structure, activity and abundance of agriculturally relevant microbes are driven by long-term fertilization strategies. Front. Microbial., 14 September, 2016. https://doi.org/10.3389/fmicb.2016.01446
Gazey, C., Davies, S. & Master R. Soil Acidity. A guide for WA farmers and consultants. 2nd Edition, Bulletin 4858, April 2014. Department of Agriculture & Food. Western Australia.
Janse van Vuuren, J.A., 1991. Prevention of detrimental effects of spatial variation in chemical properties of soils under fixed cultivation PhD Thesis, Department of Soil Science, University of Pretoria.
Janse van Vuuren, J.A. & Claassens A.S., The use of PRSTM root probes as a tool to determine the neutralizing efficacyof soil ameliorants. ISSPA 2015, 14th International Symposium for Soil and Plant Analysis. Kona Beach, Hawaii.
Wilding, L.P., 1985. Soil spatial variability, Nielsen & Bouma (eds.). In Proc. Of a workshop of the ISSS and the SSSA. Las Vegas, USA. 166 – 194.
Kodaira, M., Shibusawa, S, 2012. Using a mobile real-time soil visible-near infrared sensor for high resolution soil property mapping, Geoderma, http://dx.doi.org/10.1016/j.geoderma.2012.09.007
Thank you!