Larger bioavailability of soil phosphorus for irrigated rice compared with rainfed rice in Madagascar: results from a soil and plant survey

Abstract

Irrigated rice is less prone generally to phosphorus (P) deficiency than rainfed rice because redox reactions release P upon soil flooding. It is not known whether that is also true in highly weathered soils of Madagascar where the combination of high soil Fe and low P input may impede significant release of P. Soils and flag leaf samples were collected in 2010 in 38 irrigated rice and 46 rainfed rice fields belonging to private farmers. A critical flag leaf P content was derived from a P‐dosed pot trial study with three soils, and the results suggested 2.4 g P/kg as the critical value. Average flag leaf P was significantly larger in irrigated than in rainfed rice (2.2 compared with 1.7 g P/kg), and flag leaf P was below the critical value in 76% of irrigated rice fields while this fraction was 100% in rainfed rice. Nitrogen and K deficiencies were less prevalent. Flag leaf P increased with increasing soil pH and soil pH explained partially differences in leaf P between irrigated and rainfed rice. Flag leaf P was unrelated to soil organic matter, but increased with oxalate‐extractable soil P (Po). Multiple regression analysis revealed greater leaf P at equal soil Po and equal pH in irrigated compared with rainfed rice. Grain yield estimates (1‐m2 squares) increased with flag leaf P but not with leaf N and K. In a regression model, about 42 % of the yield variance was explained with soil Po and a rice‐growing system. The survey suggests that P is the main limiting nutrient for rice, and that soil P bioavailability is larger for irrigated than for rainfed rice in weathered soils of Madagascar.

Laboratory Visible and Near-Infrared Spectroscopy with Genetic Algorithm-Based Partial Least Squares Regression for Assessing the Soil Phosphorus Content of Upland and Lowland Rice Fields in Madagascar

“…In addition, recently, Helfenstein et al [8] revealed that the incalcitrant P fraction (NaOH-extractable inorganic P pool) turns over in weeks to months, suggesting that the incalcitrant P fraction would potentially play a significant role as a P source within a cropping season. Rabeharisoa et al [9] also found the amount of oxalate-extractable P in soils had a significant correlation with the P concentrations of rice leaves in farmers' fields in Madagascar. Therefore, we assumed that oxalate-extractable P reflects bioavailable P for rice production in the region and applied this assumption in the current study.…”

“…To improve the predictive ability, we investigated the potential to use GA-PLS regression analyses to estimate the soil P status of upland and lowland soils from laboratory Vis-NIR reflectance data. Here, we targeted amounts of oxalate-extractable P based on the above-noted field observations regarding its relative importance for rice production and on P uptake as noted by Rabeharisoa et al [9] and Nishigaki et al [6]. The predictive ability of the GA-PLS method was compared with the predictive abilities of ISE-PLS and FS-PLS methods using first derivative reflectance (FDR) spectra data.…”

Effects of organic matter addition on phosphorus availability to flooded and nonflooded rice in a P‐deficient tropical soil: a greenhouse study

“…irrigated or paddy rice) is more efficient compared to uptake by rice grown in similar nonflooded soils (i.e. rainfed or upland rice) (Huguenin-Elie et al, 2009;Rabeharisoa et al, 2012). The anoxic conditions created in flooded soils favours microbially-mediated Fe reduction.…”

Field-specific difficulties for transplanted rice to cope with ammonia from a localized enriched environment

“…Moreover, it is possible to increase the yield with increased PK application and split application of USG (Gaudin, 2012). The influence of P was already demonstrated by Rabeharisoa et al (2012).…”

“…To this effect, a mean sample was built with the volumes left by ammonia determination. Urea and ammonia were determined by colorimetric methods, respectively diacetylmonoximthiosemicarbazide (Douglas and Bremner, 1970) and indophenol-blue (Novozamsky et al, 1974) methods.…”