The phosphorus requirement ofAmaranthus mangostanusL. exceeds the ‘change point’ of P loss

Abstract

Due to the high economic value of vegetables, farmers in China often apply more fertilizer than is required for plant growth. This leads to phosphorus accumulation in soils, which can pollute the aquatic environment. This conflict arises because vegetables often use nutrients inefficiently, and require high phosphorus levels in the growth medium. In this study, amaranth (Amaranthus mangostanus L.) was grown in soils with 14.7, 23.8, 45.3, 54.6, 74.2, 101 or 116 mg Olsen-P ⁄ kg, and with and without phosphorus fertilizer (175 mg P ⁄ kg or equivalent to 385 kg P ⁄ ha). The yield of amaranth was positively correlated with soil Olsen-P content. CaCl 2 -P content was positively correlated with Olsen-P content and CaCl 2 -P markedly increased at Olsen-P contents exceeding 53.8 mg P ⁄ kg in the pot experiment or 55.9 mg P ⁄ kg in the field survey. These values were regarded as the 'change points' for phosphorus loss; to achieve 85 or 95% of maximum amaranth yield, the amaranth crop required 91or 101 mg Olsen-P ⁄ kg soil, respectively, and application of 175 mg P ⁄ kg was still able to significantly increase amaranth yield at an Olsen-P level of 74.2 mg P ⁄ kg soil. These results indicated that the phosphorus requirement of amaranth exceeded the 'change point' (53.8 or 55.9 mg Olsen-P ⁄ kg); the C min (minimum concentration in the media at which no net influx occurs) of phosphorus for 3-week-old amaranth was 1.55 lm. This value is much higher than that reported for other crops, and may explain the inefficient P use of amaranth. The high C min value also indicates that the phosphorus requirement of amaranth is beyond the 'change point' of P loss.

Stage-dependent stoichiometric homeostasis and responses of nutrient resorption in Amaranthus mangostanus to nitrogen and phosphorus addition

“…4). A previous study on Amaranth species suggested that A. mangostanus was a kind of phosphorophilous (P-like) plant36. As shown in this experiment, the N:P gr threshold (around 2.4) of A. mangostanus at the mature (flowering) stage was markedly lower than the previous reported optimal N:P value (15) for most terrestrial plants133, given that the high P demand by P-like species.…”

Phosphorus in China's Intensive Vegetable Production Systems: Overfertilization, Soil Enrichment, and Environmental Implications

“…Previous studies have reported a change‐point between soil Olsen‐P and CaCl 2 –P, the latter serving as an indicator of potential P leaching loss (Hesketh and Brookes, 2000; McDowell and Sharpley, 2001; Zhong et al, 2004; Wang et al, 2012). Above the change point, soil CaCl 2 –P has been shown to increase dramatically with Olsen‐P (Hesketh and Brookes, 2000; Liang et al, 2009). The change point can vary in different agro‐climatic regions or soil conditions (Qin et al, 2010).…”

High phosphorus at seedling stage decreases the post-transplanting fertiliser requirement of cucumber (Cucumis sativus L.)

“…Liang et al (2009) and Lu and Cao (2010) reported that soil Olsen-P concentrations above 60 mg kg −1 were suitable for vegetable growth, but that those concentrations exceeded the environmental threshold (50 mg kg −1 Olsen-P) of soil P movement. Generally, soils used for vegetable production have soil test P levels that are much greater than soils used for other forms of agriculture (e.g., grain production) (Liang et al, 2009). Therefore, strategies that minimize P application to vegetable crop soils while maintaining maximum produce yields are vitally important.…”

“…Vegetables require more external P than most other crops (Föhse et al, 1988;Liang et al, 2009). In traditional vegetable production, farmers often apply P fertilizer greatly in excess of plant requirements in the mistaken belief that this practice will boost yield.…”