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Relating topography and soil phosphorus distribution in litter-amended pastures in Arkansas
- Adhikari Kabindra, Braden Indi S., Owens Phillip Ray, Ashworth Amanda J., Charles West
- Agrosystems, geosciences & environment 2021 v.4 no.4 pp. e20207
- Mehlich-3 phosphorus, algorithms, artificial intelligence, commercial farms, fertilizer rates, landscapes, nutrient management, pastures, phosphorus, phosphorus fertilizers, poultry, risk, runoff, soil, soil erosion, streams, Arkansas
- Poultry producers in northwest Arkansas fertilize pastures with litter, leading to excessive P buildup on surface soils with risk of contaminating nearby surface waters. Information on the influence of pasture topography on P runoff is limited. Objectives were to assess soil P and P index status in pastures, quantify topographic influence on P distribution, and generate high-resolution P maps for site-specific nutrient management. Soil samples were collected from a commercial farm in a grid design and analyzed for Mehlich-3 P (STP), and dissolved reactive P (DRP). Gburek (GPI) and Sims P indices (SPI) were calculated by considering soil erosion and runoff potentials, STP, and P fertilizer application rate and source. A machine-learning algorithm, based on a random forest model, quantified spatial relationships of STP, DRP, and P indices with topography. The study area was highly variable in topography and soil P levels. High slope areas bordering streams and flat areas with lower elevation had greater GPI and SPI values. Topography explained up to 50% of variation in STP and DRP distribution and >70% variation in GPI and SPI. The key terrain attributes for STP, DRP, GPI, and SPI distribution were elevation, slope position, slope height, valley depth, and valley bottom flatness. Predicted P maps showed that areas along a stream had lower STP and DRP levels, but greater GPI and SPI. This analysis linked topographic relationships with P distribution, as topography controls the flow and distribution of water; therefore, future P management strategies should explicitly incorporate topographic risks.