PERBANDINGAN KETERSEDIAAN Fe-DTPA PADA TANAH SAWAH DENGAN RIWAYAT ROTASI TANAMAN BERBEDA DI LOMBOK BARAT

Abstract

Rice paddy soils undergo alternating wet and dry conditions that can alter redox processes and iron (Fe) availability. This study descriptively compared DTPA-extractable Fe (Fe-DTPA) in rice fields with different crop-rotation histories in West Lombok Regency. Sampling was conducted in June 2025 at three locations representing rice–rice–rice (PPP) in Labuapi, rice–rice–maize (PPJ) in Gerung, and rice–maize–maize (PJJ) in Lembar. At each location, soil was collected from five sampling points at depths of 0–20 and 20–40 cm. Samples from the five points were composited separately by depth, resulting in six composite samples. Each composite sample was analyzed three times in the laboratory; these were analytical replicates and not independent field replicates. Fe-DTPA was extracted using DTPA and measured by atomic absorption spectrophotometry (AAS). Descriptively, the highest Fe-DTPA concentrations occurred at the PPP site, with 10.10 mg kg⁻¹ at 0–20 cm and 9.09 mg kg⁻¹ at 20–40 cm. Values at the PPJ site were 6.39 and 2.84 mg kg⁻¹, respectively, while those at the PJJ site were 4.54 and 1.93 mg kg⁻¹. Fe-DTPA decreased with depth by approximately 57.5% at PJJ, 55.6% at PPJ, and 10.0% at PPP. The PPP site also had the lowest KCl pH. These patterns describe differences among three locations with different rotation histories; because each history was represented by only one location, the observations do not establish a causal effect of crop rotation. Further studies should include independent field replicates for each rotation history.