Divergent responses of leaf N:P:K stoichiometry to nitrogen fertilization in rice and weeds

Abstract

Nitrogen (N) inputs have been found to exert strong influence on leaf stoichiometry in natural ecosystems, but there are few studies investigating the effects of N in agroecosystems. Using a 5-yr fertilization experiment in rice fields, we examined the effects of N inputs on leaf stoichiometry of one crop, rice (Oryza sativa L.), and its four common weeds, barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], Monochoria korsakowii Regel and Mack, alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.], and Japanese mazus [Mazus pumilus (Burm. f.) Steenis], and further evaluated whether and how straw return mediates these effects. We found that rice and weed leaf nitrogen:phosphorus:potassium (N:P:K) stoichiometry exhibited divergent responses to N fertilizer. Weed leaf N:P:K stoichiometry was not sensitive to low (120 kg N ha−1) and regular (240 kg N ha−1) N inputs, but rice plants were, with significantly increased leaf N concentration and N:P and N:K ratios. The opposite trend was found for high N inputs (360 kg N ha−1). Rice leaf N concentration [N] did not increase further, and N:P ratios even decreased, whereas E. crus-galli and M. korsakowii had significantly increased [N] and N-related stoichiometry. We also found that the positive effects of regular N inputs on rice leaf N:P and N:K ratios were significantly dampened by straw return, but the positive effects on N:P ratios in M. pumilus leaves were enhanced by straw return. Compared with weeds, rice leaves contained low elemental concentrations across fertilization levels at grain-filling stages. These results indicate that rice has a lower N requirement than weeds at grain-filling stages, and the N supply should be managed at a relative low level to reduce the nutrient acquisition and competitive abilities of weeds. From a stoichiometric perspective, this study highlights the importance of N management in combination with straw return in controlling weeds and increasing the nutrient-use efficiency of crops.

Weeding Frequencies Decreased Rice–Weed Competition and Increased Rice N Uptake in Organic Paddy Field

“…The rice N concentration was observed to be lower at 110 DAT than at 60 DAT. Sun et al [11] explained that rice required less N during the grain-filling stages than do weeds. Weed leaves also require a high amount of nitrogen and absorb more nitrogen in highly enriched soil than do rice leaves.…”

“…Weed existence as a limiting factor in rice fields represents a serious issue hindering the achievement of an optimum rice yield [9,10]. Thus, neglecting weed growth without controlling nutrient enrichment ultimately results in a lower rice yield [11]. It has been reported that rice yield reduction caused by weeds accounts for between 15 and 76% [12].…”

Effects of Monochoria vaginalis density on yield losses, economic thresholds, and gross returns in paddy rice (Oryza sativa L.)

“…Weeds can thrive in agricultural fields where they compete with crops for space, light, nutrients, and water (Bajwa et al., 2020; Garrity et al., 1992; Mushtaq et al., 2020; Sun et al., 2019). Weed management using herbicides is the most common practice for reducing crop yield losses in agricultural production(Kaundun, 2021; Liu et al., 2020).…”

“…(Fischer et al., 2001). Evidence suggesting that the ability of paddy rice to suppress these weeds is highly correlated with the growth characteristics of the rice plants at maturity (Garrity et al., 1992; Sun et al., 2019). The early growth characteristics of rice plants was also shown to have a greater effect on weed suppression than direct seeding and transplanting in upland rice (Ni et al., 2000; Tachibana & Watanabe, 2001).…”