Transformation of crystalline and short-range order minerals in a long-term (47 years) rice-rice cropping system

Abstract

The effect of long-term fertilizer and manure applications on short-range order (SRO) and crystalline mineral transformation was studied in a 47-year puddled rice-rice cropping system experiment in Odisha, India. The relationship of SRO minerals with phosphorus and potassium fixation capacity and soil carbon fractions was also evaluated. Soils from different treatment combinations of farmyard manure (FYM), nitrogen (N), phosphorus (P) and potassium (K) were separated in two ways: (i) removal of binding materials (ii) non-removal of binding materials (ultrasonic vibration), followed by fractionation of the contents into silt and clay. All crystalline minerals, SRO minerals, P and K fixation were measured in silt and clay. The X-ray diffractograms of clays (<2 μm) were recorded in Philips Diffractometer (model PW 1710). Selective dissolutions of SRO minerals were carried out by extraction with sodium hydroxide, acid ammonium oxalate, dithionite-citrate-bicarbonate and sodium pyrophosphate. The results showed that the soils were composed of kaolin (49.6–54.4%), mica (32.7–39.0%) and smectite (10.6–17.0%). The clay-size mica loses its crystallinity and becomes finer after the addition of fertilizers and manure during intensive rice cultivation. The content of amorphous ferrialuminosilicate varied from 8.0 to 16.23 g 100 g􀀀 1 in clay and 1.49–3.38 g 100 g􀀀 1 in silt. The plots treated with NP + FYM had the highest total oxalate extractable oxide in both clay and silt. Application of FYM increased ferrihydrite in both clay and silt. Potassium fixation was higher in plots skipped with the long-term application of K. Formation of SRO minerals was positively affected by nutrient stress caused by the omission of one or more nutrients. SRO minerals in the rice soil did not have a major effect on the fixation of K and P; rather, it is controlled by the fertilizer and FYM application. However, carbon fractions had a significant positive correlation with SRO minerals.