Applied phosphorus (P) use efficiency is generally low due to the low mobility of P in soil and its affinity to form insoluble complexes. Localized P application nearby the root zone is a potential approach to overcome this issue in crop production. However, the interaction with soil conditions is little understood, which results in less effective application of this approach. Using root-box experiments and changing P-retention capacity of soils, we revealed that applied P use efficiency of rice can be substantially improved by dipping seedlings in P-enriched slurry at transplanting (P-dipping) even in highly P-fixing soils. Spatial analysis of soluble P in soils indicated that P-dipping creates a P hotspot because the P-enriched slurry is transferred with seedling roots. The P hotspot could have induced vigorous surface root and facilitated further P uptake from the spot. In contrast, the effect of conventional P incorporation depended on P-retention capacity of soils; no increases in soluble P content in soils or plant P uptakes were observed when P-retention capacity was high. Our finding of significant interaction between localized P application and a specific soil property should help improving applied P use efficiency and achieving sustainable rice production against depleting P fertilizer resources.
Given the finite nature of P fertilizer resources, it is imperative to investigate effective P management practices in order to achieve sustainable rice production. This study was conducted (1) to assess the effect of dipping rice seedlings in P-enriched slurry before transplanting (P-dipping, hereafter) on initial plant growth and (2) to determine the optimum P concentration and dipping duration. In the P-dipping treatments, four P2O5 concentrations in the slurry (4.3%, 5.0%, 6.0%, and 7.5%) and four dipping durations (0.5 h, 2 h, 4 h, and 8 h) were investigated. After the treatments, the seedlings were transplanted into 1/5000 Wagner pots and grown under flooded conditions for 42 days and they were compared with plants under conventional P incorporation at the rate of 300 mg P2O5 pot−1 and with plants under no P application. The amount of P2O5 attached to P-dipped seedlings, or locally applied in the rhizosphere at transplanting, increased with higher P concentrations in the slurry, ranging from 87.5 to 112.2 mg pot−1. Shoot biomass at 42 days after transplanting (DAT) was greatly increased in plants under the P-dipping treatments, compared to that in plants with no P application and was comparable to or greater than that in plants under conventional P incorporation, even when P levels were 2.5 to 3 times lower. Among the P-dipping treatments, we observed some significant effects of P concentrations and dipping durations on seedling P uptake and shoot biomass, without any interaction between these variables. Seedling P uptake and biomass tended to be higher with higher P concentrations in slurry and longer dipping durations. Conversely, the shoot biomass at 42 DAT was significantly lower in plants under the highest P concentration treatment (7.5% P2O5) compared to that in other plants and tended to be lower with longer dipping durations (4 h and 8 h). These negative effects can be attributed to the slow recovery from transplanting shock because of the chemical damage of seedlings exposed to higher salt concentrations for longer durations. The present study highlights that (1) P-dipping could be an effective approach to increase transplanted rice production with minimal P inputs, and (2) this effect could be higher with a low P-concentration in the slurry (4.3% P2O5) and a short dipping duration (0.5 h). Based on the obtained results, further on-farm trials are expected to assess farmers’ appreciation and the potential constraints of adopting this technique.
The majority of paddy fields in sub-Saharan Africa (SSA) are characterized by nutrient-poor soils. In such fields, tillering in rice plants is severely restricted, which results in a reduced number of panicles and thus a decrease in grain yield. In this study, we evaluated the effects of a quantitative trait locus (QTL), associated with number of panicles and referred as MP3, on rice growth and grain yield in nutrient-poor soils in Madagascar. We used a high-yielding rice cultivar, "Takanari", and its near-isogenic line bearing the MP3 allele (NIL-MP3). A pot experiment with various P application rates demonstrated vigorous tillering in NIL-MP3 compared to Takanari from the early vegetative stage even under low P levels. This led to enlarged leaf area and thus increased biomass. We then conducted multiple field trials with a total of 12 experimental conditions using the two varieties. The experiments led to a range of grain yield from 1.3 to 4.1 t ha-1 and a range in number of panicles from 107 to 270 m-2. The results revealed that NIL-MP3 produced a greater number of panicles and spikelets m-2 (19% and 12%, respectively) than Takanari across all 12 experiments. Grain yield increased in NIL-MP3 under some experimental conditions. This study is the first of its kind to demonstrate that MP3 increased number of panicles and spikelets and grain yield in the nutrient-poor and low-yielding soils of SSA. Thus, we conclude that MP3 could become a prominent genetic resource for the improvement of rice yields in SSA.
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