Distribution and Dynamics of Soil Phosphorus across Textural Gradients under Long-term Phosphorus Application in Partially Irrigated Arable Lands of Arid Thar Desert

Abstract

In arable ecosystems, the bioavailability and environmental fate of phosphorus (P) are heavily dictated by soil physical properties and phosphorus management. This study investigates the distribution and dynamics of soil P across a textural gradient under long term P management in arable arid lands. The soil samples were collected from the study area using three tier approach i.e., pre-field image interpretation of arable lands, sample collection at 2 to 3 km distance using 5 km2 grid followed by laboratory analysis. Entisol and Aridisol are the dominant soil order having deep to very deep soil with coarse texture and poor fertility. Using a sequential P fractionation scheme, the soil P was quantified into available, labile, mineralizable, and stable pools. The average values of total soil P ranged from 328 to 490 mg kg-1 which is comprises of inorganic (61 to 74%) and organic P (26 to 39%) among textural groups. Significantly higher average amount of total and inorganic P were observed in sandy loam to loam (469 to 490 mg kg-1 and 349 to 363 mg kg-1) then the sandy (328 to 364 mg kg-1 and 201 to 238 mg kg-1) soils, respectively. However, nonsignificant difference was observed in soil organic P (121 to 127 mg kg-1). Overall, higher content of P fractions were observed in sandy loam to loam soils with appreciable increase in calcium phosphates except aluminum-P (Al-P) and occluded-P (Occl-P) which were higher in coarse textured sandy soils. Based on degree of extractability of different soil P fractions, about 51 to 61% of the total soil P was recovered in stable P pool and rest may have potential for reversible accessibility in these soils. Of that about 22 to 34% was observed as mineralizable P, 7 to 9% as labile P and only 2 to 3% was observed as available P pools. Significantly higher P concentration was observed in fine-textured soils (SL to Loam) for stable (~21%), mineralizable (~97%), and labile P (~29%) pools while slight increase (~9%) was observed in available P pool than coarse textured soils (FS and LS). Further, calcium phosphates (i.e., dicalcium-P; DC-P, octacalcium-P; OC-P & hydroxyapatite-P; HA-P) and iron-P (Fe-P) dominant in fine textured soils whereas higher Al-P and Occl-P was observed in coarse textured soils. No specific trend was observed for phytate-P (Phyt-P) in these lands. These results indicate that soil texture is an important determinant of P storage showing variable retention capacity for specific P pools in these arable lands. Specifically, fine-textured soils exhibited a greater proportion of moderately labile P, whereas coarse-textured soils were characterized by lower retention and a higher risk of P leaching through the profile. Therefore soil texture based P management may lead to better P use efficiency and to prevent environmental runoff losses in arable lands of arid regions. This research provides a fundamental basis for site-specific P management in diverse arable landscapes.