Agronomic performance, seed quality and nitrogen uptake of Descurainia sophia in response to different nitrogen rates and water regimes

Abstract

Descurainia sophia (flixweed) is an annual weed widely distributed in cultivated crops, forage and rangelands throughout the world. This weed, in particular its seed, is used for food, medicinal and industrial purposes. The objective of this study was to investigate the effects of irrigation management and different application rates of nitrogen on morphological traits and yield components of this weed as a means of enhancing production and economic returns. A two-year field experiment was conducted in a semi-arid region in Iran during the 2009–2010 and 2010–2011 growing seasons. The experiment was a split plot in a randomized complete block design with three replicates, with irrigation treatments as main plots and nitrogen rates as sub plots. The three irrigation regimes consisted of 0.1 maximum allowable depletion or deficiency (MAD) of available soil water (ASW), 0.2 MAD of ASW, 0.4 MAD of ASW in 2010 and 0.2 MAD of ASW, 0.4 MAD of ASW and 0.8 MAD of ASW in 2011. The plants were grown at three nitrogen rates of 0, 200, and 300 kg N ha⁻¹. Generally there were significant increases in seed yield, biomass, straw yield, harvest index, number of siliques (pods) per plant, seed weight, plant height, time to maturity, water use efficiency, protein concentration in seed, straw N concentration, nitrogen uptakes and nitrogen harvest index each growing season by applying nitrogen at all irrigation treatments. There was a decreasing trend in number of plants per m², nitrogen utilization efficiency and oil concentration with increasing nitrogen application under all the irrigation treatments. Seed yield response to irrigation treatments and N rates seemed to be more related to number of plants per m² and number of siliques per plant. The highest seed yield was obtained at the plant population of 686 plants per m². The results obtained here suggest that nitrogen application can improve the seed yield and seed quality of D. sophia grown under different irrigation regimes. Averaged over both years, the application of 300 kg N ha⁻¹ under 0.2 MAD of ASW resulted in the highest revenue; 200 kg N ha⁻¹ was not significantly different to 300 kg N ha⁻¹.

Introduction

Descurainia sophia (L.) Webb ex Prantl (flixweed) is an annual weed (Brassicaceae family), widely distributed in cultivated crops, forage and rangelands throughout the world (Mitich, 1996, Baskin et al., 2004, Blackshaw et al., 2005, Hernandez Plaza et al., 2011, Li et al., 2011). This weed, in particular its seed, is used for food, medicinal and industrial purposes (Mitich, 1996, Peng et al., 1997, Bekker et al., 2005, Sun et al., 2005, Mohamed and Mahrous, 2009, Li et al., 2010, Mosaddegh et al., 2012). D. sophia seeds contain over 25% protein, 22–44% oil, 3.5–4% ash and around 7.6% fiber (Tkachuk and Mellish, 1977, Duke and Ayensu, 1985, Peng et al., 1997, Bekker et al., 2005). In general, the economic value of D. sophia production is determined primarily by the attainable seed yield and less by the seed compounds such as oil concentration.

Processes of yield formation are highly variable and depend on genetic, environmental and agronomic factors as well as their interactions (Rathke et al., 2006). Among the various inputs, water and fertilizer (nutrients) are considered as the two key inputs making maximum contribution to plant productivity (Lenka et al., 2009). Water is considered the most limiting factor for plant production in arid and semi-arid regions. In these regions, the unfavorable distribution of rain over the growing season and the year-to-year fluctuations represent a major constraint to plant growth. In crop production systems, more production per unit water applied is the main concern (Rostamza et al., 2011). During greenhouse trials measuring water use efficiency, D. sophia displayed inefficient usage of water (Anderson and Best, 1965). Nitrogen is currently the most widely used fertilizer nutrient and the demand for it is likely to grow in future. Since nitrogen is a component of protein and nucleic acid, when nitrogen amount in soil is not optimal, growth is reduced (Sepaskhah and Barzegar, 2010). There are some reports indicating that D. sophia responds positively to nitrogen fertilization (Bischoff and Mahn, 2000, Blackshaw et al., 2005).

Increasing the plant production and enhancing economic returns is highly correlated with the application of optimum amount of water and nitrogen fertilizer. To our knowledge, there are no studies which assess production ability, water use efficiency and nitrogen uptake behavior of D. sophia under different conditions of water and nitrogen. Therefore, the main objective of this study was to investigate the effects of irrigation management and different application rates of nitrogen on this industrial-medicinal plant taking into account both quantity and quality aspects.