Importance of phosphorus and potassium in soil-specific nutrient management for wet-season rice in Cambodia

Abstract

Rice is widely grown in rainfed lowlands during the wet season in the Mekong region. Limited nutrient availability is a common constraint on crop yield, and the optimal rate of fertilizer application depends on the soil type. The objective of our study was to evaluate rice productivity and the economic feasibility of various nutrient management regimes in Cambodia. We conducted field experiments on three soil types (Prey Khmer, Prateah Lang, and Toul Samroung, equivalent to Psamments, Plinthustalfs, and Endoaqualfs, respectively) in four provinces (Battambang, Kampong Thom, Pursat, and Siem Reap) during the 2016 and 2017 wet seasons to compare nine (2016) and seven (2017) N–P–K combinations. Grain yield ranged from 0.9 to 4.8 t ha−1 in 2016 and from 1.0 to 5.2 t ha−1 in 2017, depending on soil type and nutrient management. The Prey Khmer soil contained around 80% sand, and rice yield responded most weakly to nutrient management. The moderate fertilizer input in the current soil-specific recommendation was effective on this soil type. However, on more fertile soils with a higher clay content and a higher cation-exchange capacity (Toul Samroung and Prateah Lang), an additional 20 kg N ha−1 combined with adding 15 kg ha−1 of P2O5 or 20 kg ha−1 of K2O significantly increased yield and economic return. Although P and K use during Cambodia’s wet season is uncommon, our results demonstrate the importance of these nutrients in improving the country’s rice production.

Potential yield and nutrient requirements of direct-seeded, dry-season rice in Cambodia

“…For those farmers willing to invest more in dry-season rice cultivation on Toul Samroung soil, adding N and K to the soil-specific recommendation would slightly increase productivity without reducing profits. For wet-season rice, in contrast, we previously showed that additional fertilizer inputs into soil-specific management significantly and consistently improved profits (Kong et al, 2019). There could be three reasons for the different implications of the nutrient requirements between dry-and wet-season rice.…”

“…One is that the growth duration is much shorter in non-photoperiod-sensitive cultivars in the dry season than in photoperiod-sensitive cultivars in the wet season. The other is that the recommended rates for dry-season rice (Table 3) are much higher than those for wet-season rice (57-63 kg ha −1 of N, 23-38 kg ha −1 of P 2 O 5 , and 0-35 kg ha −1 of K 2 O on Toul Samroung and Prateah Lang soils; Kong et al, 2019), reflecting the fact that farmers apply more fertilizer in the dry season than in the wet season, particularly N and P (Fukai and Ouk, 2012). In addition, the frequent loss of standing water in wet-season rice, usually grown under rain-fed lowland conditions, might accelerate the N loss through denitrification or leaching (Buresh et al, 2019).…”

“…Coarse-textured infertile soils lacking sufficient N, P, and K limit rice yields in Cambodia (Kong et al, 2019). Following a large national soil survey, the soils were classified into 11 groups according to their nutrient management requirements: Bakan, Kampong Siem, Kbar Po, Kein Svay, Koktrap, Krakor, Labansiek, Orung, Prateah Lang, Prey Khmer, and Toul Samroung (White et al, 2000).…”

“…Potential yield is the yield of a cultivar grown in environments to which it is adapted with non-limiting water and nutrient conditions (Evans and Fischer, 1999). Our previous field experiment showed that the best nutrient management gave yields of a popular photoperiod-sensitive cultivar ('Phka Rumduol') as high as 5.2 t ha −1 in the wet season (Kong et al, 2019). However, little is known of the experimental potential yield (i.e., best yield from experiments; Stuart et al, 2016) or the economically attainable yield (i.e., best farmers' yield) of dry-season rice in the region.…”

Managing Sands of the Lower Mekong Basin to Limit Land Degradation: A Review of Properties and Limitations for Crop and Forage Production

“…Leaching of N and other nutrients may also limit productivity of these soils. The Prey Khmer soil in Cambodia has low potential productivity for wetland rice even following recommended rates of fertilizer application [12,54,55].…”