Soil Phosphorus and plant nutrition

Dynamic of P forms in soils of the SW Pampean region: Incubation with phosphorus fertilizer

Different soil P forms exist in a dynamic equilibrium, which depends on the edaphic atmosphere (texture, MO and pH) and on the agronomic management practices (crop rotation and fertilization).The objective of the study was to assess the effect of P application on a soil on the equilibrium of this element. Nine soils were selected and 0, 50 and 100 ìg of P g-1 were added to these soils. Subsequently, the soil-P mixtures were incubated during 0, 90, 180 and 360 days. The P addition produced an initial decrease of the analyzed P forms. This decrease was more pronounced and persistent in time in the shallow soils. The amount of P-Fe+Al formed during the studied period depended on the soil Fe+Al:Ca relationship, reaching maximum values when the ratio was around 15. In addition, the amount of P-Fe+Al was variable in time and reached maximum values after 180 days of incubation. On the other hand, the formation of P-Ca was much more variable and presented important changes in time. The P balances in shallow soils changed throughout the incubation period; P that was not detected at days 90 and 180 was detected at day 360. These samples were analyzed by electron microscopy and the presence of crystallized substances was observed on days 90 and 180, indicating the formation of P metastable compounds which could be one of the transformations that this element suffers in time.

Key words. Phosphorus fractions, Calcareous soils, P recovery.

Suñer L. & J.A. Galantini. 2013. Dinámica de las formas del P en suelos de la región sudoeste pampeana: Estudio de la incubación con fertilizante fosfatado. Ciencia del Suelo 31: 33-44                PDF (In Spanish)

Phosphorus Fertilization in Wheat Crops in Southwest of Pampas Region

Fertilization with P modifies the balances between the different forms in which it is in the soil and alters the availability and the nutrition of the plants. The objectives were to determine the influence of some properties of the soil on the necessary rate to increase a unit the available phosphorus (Pe) and the effect of the application of phosphorus on the production of dry matter, the response and the balance with other nutrients in wheat (Triticum aestivum). There was realized a fertilization experiment of wheat with P (0, 25, 50 and 100 kg ha^-1) in pots with nineteen soils (0-0,20 m) different. There was analyzed the available phosphorus (Pe) to the beginning of the experiment and in the moment of the sampling plant (booting). It was determinated N, P, K, S in plant and it was calculated the balance with other nutrients. The average rate was 2,7 kg P ha^-1 (with values between 1,2 and 4,8 kg ha^-1). The initial Pe and the content of organic matter associated with the mineral fraction (MOM) were the properties that better explained the variability. The increase of the P rate applied increased the produced dry matter and the concentration of P. These changes were associated at the level of initial Pe, aspect that was reflected in the balance of nutrients in plant. The concentration of N, K and S it was not modified, but it increased significantly the quantity. Conclusion is that from the point of view of the balances physicist - chemist of the phosphorus, the characteristics of the soil, especially Pe and MOM, determine the dynamics and the final pool of the applied phosphorus. From the point of view of the plants, the fertilization modifies the response, the absorption and the balance with other nutrients.

Keywords: Soil Phosphorous, Wheat dry matter, Nutrient balance,  DRIS

Suñer L. G. & J. A. Galantini. 2012. Fertilización fosforada en suelos cultivados con trigo de la región pampeana. Ciencia del Suelo 30(1) 57-66.                                                   LINK (In Spanish)

Long-term crop rotation effects on organic carbon, nitrogen, and phosphorus in Haplustoll soil fractions

Rosell, R.A., Galantini, J.A., Suñer, L.G. 

Soil organic matter (SOM) or carbon (SOC) consists of a number of fractions (which can be separated by granulometric wet sieving) having different properties among them. Information on fraction nutrient distribution and long-term crop rotations is lacking for semiarid environments. The objective of this research was to study the agronomic effects on soil OC, N, and P fractions. The humified OC was the largest and least variable fraction of the SOC. Soil under continuous mixed pasture had higher OC contents than under annually tilled treatments. Similarly, soil total nitrogen under the cropped treatments decreased from 1.7 g N kg^-1 in noncultivated soils (reference plots) to 1.0, 0.7 an 0.7 g N kg^-1 under mixed pasture, pasture-crop, and wheat-crop respectively, in the fine soil fraction. The reference plots also showed significantly lower levels of organic phosphorus (Po) in comparison to the other treatment (from 67.1 μg Po g^-1 to greater than 100 μg Po g^-1 in the fine fraction of the treatments and years). The noncultivated soil showed larger values of P(o) and inorganic P in the large-size granulometric fraction (0.1-2 mm) than in the soil fine fraction (0-01 mm). However, the rotation treatments had greater concentrations of P in the fine fraction. The Po from the coarse fraction appears to be the most labile and sensitive fraction to tillage and environmental conditions, and may be closely related to P availability.

Keywords: Inorganic P; Organic P; Semiarid soil fractionation; Tillage systems, crop rotation; semiarid region; soil carbon; soil nutrient

Rosell R.A., J.A. Galantini, L.G. Suñer. 2000. Long-term crop rotation effects on organic carbon, nitrogen, and phosphorus in Haplustoll soil fractions. Arid Soil Research and Rehabilitation 14 (4) 309-315

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