N-Budgeting For Crops

N-Budgeting For Crops:

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August 19, 2013

PART 1

Using David Herridge’s Nbudget to estimate amount of N to be applied

N-Budget is an Excel-Based, simple-to-use calculator developed to assist farmers as well their advisers within northern grains of Australia to estimate water levels and soil nitrate during sowing and the N requirement for oilseeds and cereals. This tool also gives estimates of how much of N fixed by legume grain crops (David, 2011).

Calculation Using NBudget

This section offers calculations of how NBudget tool were used to estimate the amount of N applied for Dubbo (paddock) during winter and summer cropping, and the timing is within the sowing month.

Dubbo was selected from the site details on the dropdown list. The names of the paddock and farm were typed or (inserted) as shown is fig 1. The paddock is portrayed to be of medium fertility, for instance medium use of fertilizer N and pulses. The type of soil is red-brown.

Two seasons earlier

From the dropdown list, I chose the crop cultivated in the paddock the season prior to the last.Two seasons ago, the crop within the paddock was N-fertilized canola (obtained from the drop-down list). The post-fallow soil N estimate, for example at the beginning of the previous season, is found to be 62 kg N/ha. Had the paddock would have been cultivated; the value could have been about 20% more.

Previous Season

Nbudget then gives soil nitrate estimates of past fallow, for instance soil nitrate at the moment the advisor or farmer is making decision regarding fertilizer N inputs for the next cropping season. From the dropdown list I selected the crop that was cultivated in the paddock, then inserts protein, (if it is cereal crop), yield and amount of N fertilizer applied. The results are; Fertilized with 70 kg N/ha, wheat yielding is 2.1 t/ha and 13.0% of grain protein.

Present Summer Fallow- The estimates of the Nbudget is 67 kg N/ha soil nitrate at sowing. At sowing, soil water is estimated at 75 mm derived from the selected fallow rainfall of 243 mm.

Targeting proteins and grain yields, Requirements of fertilizer N

The estimated grain yields for the next season are automatically calculated using default values of WUE (Water Use Efficiency). The protein default values are 9.5%, 10%, 13, 11.5% for sorghum, barley, durum and bread wheat respectively. Grain proteins for fababean, chickpea, and canola are at default values, which do not need to be changed.

The N requirement for oilseed crops and cereals and the N amounts fixed by these legumes are then worked out together with the post fallow (residual) nitrate levels.

Fig 1 Calculations Using NBuget

The N-tool wheat yield projections were 2.4, 3.1 and 3.7 t/ha for the 30 percentile (poor), 50 percentile (average) and 70 percentile (good seasons) requiring 78 kg N/ha. The project grain proteins ranged from 12.7% to 10.7% during poor and good seasons respectively. The projected yields of durum were nearly the same, with 50% higher N requirements at 117 kg N/ha. On the other hand, Barley was projected to yield approximately 30% more but significantly less N fertilizer i.e. (35 kg N/ha). The projected yields of canola was 1.2-1.9t/ha, and requiring approximately 100 kg N/ha. The tool predicted that fababean and chickpea could yield about 3.0t/ha and fix nearly 155 kg H/ha, based on the season and pulse.

The nitrate levels for the post fallow, for instance soil nitrates in the next 12 months, were also projected for all the six crops for various seasonal cases. The values were ranging from 3 kg N/ha following high yielding (good season) barely to over 80 kg N/ha following fababeans and water stressed (low yielding) durum crops and canola.

PART 2

Factors that Affects N dynamics and Estimation of N requirements

De-nitrification

According Bonde, Christensen & Cerri (2002), denitrification is a process through which nitrate is changed into gases (nitrous oxide or dinitrogen) and hence, are released into the atmosphere. This process can be an essential means for N loss on fine and medium textured soils. Some of environmental elements that determine whether denitrification happens and to what degree include;

Nitrate: It must be available for denitrification to happen. If it is in low levels or absent, the denitrification losses would be less.

Aeration and Soil water level: Denitrification happens in wet soils of low concentration of oxygen and it increases with duration of time that the soil is saturated. Lodged water would cause more nitrate percentage to be denitrified.

Soil Organic matter (SOM): Soils that have low soluble OM have less likelihood for denitrification as opposed to soils with greater soluble OM. Hence nitrate, which resides below 12 inches deep into the soil profile where there is minimal OM will have a minimal or greatly reduced denitrification probability.

Effect of Soil Organic Matter on the rate of mineralization

Soil OM decomposition and consequent release of inorganic N happens through the activity of fungi and bacteria (Molina, Clapp, Larson, 2005). Soil mineralogy and environmental elements influence the actions and players of microflora, which subsequently determine the N mineralization rate within the soil and hence the mineralized amount over time. Climate reacts with soil properties, comprising the soil’s microflora to affect the chemical nature and size of the soils N pool. Moisture content and soil temperature have major effect over N mineralization activities. Optimal N mineralization happens at 30-350C of soil temperature. Dry soils have low N mineralization due to low microbial activity. Lack of O2 in saturated soils reduces N mineralization.

Significance of Taking sufficient cores while soil sampling

According to Gilmour, Cogger, Jacobs, Evanylo, (2010) taking enough cores helps one to have composite soil samples, (samples which include as opposed to excluding) and hence the fertilizer band will have the minimal variation or deviation from the “actual”/true values.

References

Bonde, T.A., Christensen, T & Cerri, C . (2002). Dynamics of soil organic matter as

reflected by natural 13C abundance in particle size fractions of forested and cultivated

Oxisols. Soil Biol. Biochem. 24:275-277.

Gilmour, J. T., Cogger, C. G., Jacobs, L. W., Evanylo, g. K., Sullivan, D. M. (2010).

Decomposition and plant available nitrogen in biosolids: laboratory studies, field studies,

and computer simulation.” J. Environ. Qual. 32: 1498-1507.

Molina, J.A.E., Clapp, C.E., Larson, W.E., (2005). Potentially mineralizable nitrogen in soil: the

simple exponential model does not apply to the first 12 weeks of incubation. Soil Science

Society of America Journal 44, 442–443.

David H, (2011), NBudget’ – a nitrogen management tool for cropping systems retrieved from

HYPERLINK “http://www.grdc.com.au/Resources/Bookshop/2011/10/Managing-Legume-and-” http://www.grdc.com.au/Resources/Bookshop/2011/10/Managing-Legume-and-

Fertiliser-N-for-Northern-Grains-Cropping