Effect of nitrogen application on the expression of drought-induced root plasticity of upland NERICA rice

Daniel Makori Menge,John Collins Onyango,Akira Yamauchi,Mana Kano-Nakata,Shuichi Asanuma,Tran Thiem Thi,Yoshiaki Inukai,Mayumi Kikuta,Daigo Makihara

doi:10.1080/1343943x.2018.1561194

Daniel Makori Menge, John Collins Onyango + Show 7 more

Open Access

https://doi.org/10.1080/1343943x.2018.1561194

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Abstract

ABSTRACT This study evaluated the effect of three N fertilization levels 60 (low), 120 (medium), and 180 (high) kg N ha−1 and soil moisture content gradients created by a line-source sprinkler on the expression of plasticity in lateral root branching and dry matter production (DMP) of upland new rice for Africa (NERICA) 1 and 4. There were no significant differences in DMP between NERICA 1 and 4 under well-watered, mild drought, and severe drought conditions regardless of N level. In contrast, under moderate drought (12–21% v/v of soil moisture content [SMC] in 2011 and 16–24% v/v of SMC in 2012), NERICA 1 had significantly higher shoot dry weight, total root length (TRL), lateral root length, and branching index than NERICA 4 at medium and high N; however, there was no significant difference between the two NERICAs in DMP at low N. TRL of NERICA 1 was significantly higher under moderate drought than well-watered conditions, but only with medium and high N. Regardless of N level, moderate drought did not enhance NERICA 4’s root system. Thus, NERICA 1’s root system exhibited plastic development, promoting lateral root branching at medium and high N. These morphological changes were associated with the greater DMP in NERICA 1 than NERICA 4 under moderate drought, whereas the lack of such plasticity at low N meant genotypic differences in DMP were obscured. Our findings implied that N application can improve upland NERICA productivity under moderate drought conditions, but differences in variety and field conditions may influence efficacy.

Highlights

In the 2015/2016 cropping season, Africa produced approximately 19 million tons of milled rice and consumed 30 million tons (USDA, 2017)
We showed that enhanced root growth in a shallow soil layer was a key trait in upland new rice for Africa (NERICA) that are adapted to drought stress (Menge et al, 2016)
This study examined how N fertilization affected upland NERICA 1 and 4 root plasticity when deep root growth is impeded in comparison with Lemont, a lowland variety

Summary

Introduction

In the 2015/2016 cropping season, Africa produced approximately 19 million tons of milled rice and consumed 30 million tons (USDA, 2017). The continent spent approximately 8 billion USD importing rice during that season, accounting for 30% of global rice imports. African demand for rice is the fastest growing demand worldwide (IRRI, 2017), driven by rapid urbanization and a shift in consumer preference from the traditional staples to rice (Balasubramanian et al, 2007). Urgent measures are necessary to increase rice production in Africa, thereby reducing production deficits and import expenses. With the exception of Egypt and Mauritania, very little rice cultivation occurs on irrigated fields in African countries (Seck et al, 2012). Rice is primarily cultivated in rainfed upland fields, which constitute about 45% of the rice-growing area in sub-

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