Agronomic Aspects of Nitro phosphate Based Complex Fertilizers

Dr. W. WICHMANN

BASF Aktiengesellschaft, Agricultural Research Station, Limburgerhof, Germany

Balanced plant nutrition, which provides the Fertilized crop with all required nutrients in the appropriate ratio, is most easily achieved by using a multinutrient fertilizer. Depending on the soil's nutrient status, either an NP or an NPK fertilizer is used in practical agriculture for a balanced basal fertilizer application as a foundation for a high yield.

Among the multinutrient fertilizers available, homogeneous complex fertilizers produced by the nitro phosphate process offer a number of advantages over other fertilizer types. Due to their specific production process, i.e. the acidification of rock phosphate with nitric acid, the subsequent addition of ammonia and, in the case of NPK-formulas, the incorporation of a potassium salt into the melt, nitro phosphates contain all their fertilizer nutrients in the prescribed ratio, not only in one bag, but in every granule. Therefore, unlike in a bulk blend, the nutrients are not liable to segregation during handling, transport and application.

The nutrient ratio in nitro phosphates can be varied to meet the requirement of most soil/crop combinations, in contrast to mono or diammonium phosphate with their fixed N/P ratios.

From these facts result advantages for nitro phosphates with regard to:

logistics,

decision making by the farmers,

handling and application,

plant nutrition,

environmental aspects.

Logistics Advantages

The combination of nitrogen, phosphate and where required - other fertilizer nutrients in one material implifies distribution planning and transport of the fertilizer to the retailers. This is of special importance in regions with inadequate infrastructure where the use of straight fertilizers entails the risk that not all necessary fertilizer nutrients will be available to the farmer at the correct time for application. The reduced number of different fertilizers to be distributed makes planning easier and saves costs for transport and storage.

The good physical characteristics of nitro phosphates i.e. high crushing strength of the granules, high abrasion resistance, low caking tendency, low dust content and thus low risk of caking and deterioration) give this type of fertilizer excellent properties to sustain the vagaries of transport and storage - also if conditions are not ideal.

Simplified Decision Making

To follow the recommendations for a balanced crop nutrition by application of all fertilizer nutrients, the farmers no longer have to buy several straight fertilizers in the correct proportion. Instead, one nitro phosphate formula will generally be sufficient to achieve this purpose. One NPK fertilizer can replace three straight N,P and K fertilizers. This simplified approach to the concept of balanced fertilization is a valuable educational tool to familiarize farmers with this concept and to prevent one-sided nitrogen fertilization with its negative consequences. The continued emphasis on nitrogen application only - as this fertilizer nutrient generally gives the most convincing visual effects and yield increases - will sooner or later result in reduced fertilizer N efficiency as other nutrients become deficient in the soil due to the enhanced crop growth and thus greater requirement of all nutrients. Only a balanced fertilization with all nutrients prevents this development.

With the uniform appearance of all granules in a bag of nitro phosphate, there is no risk of adulteration and the farmer can be sure to receive the nutrients he has paid for in a top-grade fertilizer.

Reduced Workload with Handling and Application

In consequence of the above, when using nitro phosphate farmers have to handle only one fertilizer percentage of nitrate, nitro phosphates can also be used for application to rice grown on waterlogged soils.

The phosphate in nitro phosphates is totally plant available, partly water-soluble for immediate uptake, partly citrate-soluble for conversion into water-soluble, phosphate forms under the effect of soil acidity. Nitro phosphates produced with the present modern technology contain upto 80 percent of their phosphate in water-soluble form. This is much more than the 50 percent water-solubility demanded by Indian agronomists for optimum performance as a result of field trails. With this high solubility nitro phosphates are also suitable on neutral to alkaline soils, for crops with a short growing period and with low P₂O₅ application rates, which require a large percentage of water-soluble phosphate.

The combination of water and citrate soluble phosphate has then the advantage that the phosphate is less prone to fixation than with a fully water - soluble P-fertiliser where the P not taken up by the crop immediately risks to be transformed in the soil into insoluble forms of phosphate.

Where required potassium is added in the production of nitro phosphates so that NPK multinutrient fertilizers with the desired nutrient ratio are obtained. Though generally potassium is added as KCI for cost reasons, K₂SO₄ can be used where crops susceptible to chloride (e.g. tobacco) are to be fertilized.

Sulphur, which over the last years has been recognized more and more as an important fertilizer nutrient, is contained in significant quantities in many nitro phosphate formulae. It originates mainly from the ammonium sulphate incorporated as filler substance and/or from potassium sulphate where this material is used as the K source.

Table 1: Effect on Cereals of an NPK Complex Fertilizer 13-13-21 and a Bulk Blend of the same Formula

Results 1989, yields in t/ha

Furthermore, the possibility to incorporate other (secondary and micro-) nutrients into a nitro phosphate offers an effective way to include such elements into the fertilizer practice in areas where known deficiencies exist. It has also to be noted that, because of their chemical composition, nitro phosphates have only a small acidifying effect on the soil, a fact especially beneficial under humid conditions.

Benefits to the Environment

The absence of amide-N (urea) results in significantly lower volatilization losses from nitro phosphates than from urea and other fertilizers containing this form of nitrogen. As a result not only is the fertilizer efficiency of the N in nitro phosphates better, but they also contribute less to possible NH₃ emissions into the atmosphere.

Whereas nitro phosphates produced with previous technology contained about 40 percent of their nitrogen as nitrate, this share has been reduced to as little as 32 percent in some of the current formulas. With this reduction the risk of N-losses by leaching or denitrification have been consequently reduced.

The savings in transport and application, which are achieved with nitro phosphates, help to conserve energy.

All these above advantages make nitro phosphates a superior alternative to straight fertilizers, bulk blends and other types of multinutrient fertilizers.

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