Modelling NUE

SP5 addressed the issue of cropping system level NUE with the recognition that NUE varieties need to be incorporated into NUE systems if they are to achieve their full potential. The incorporation of these varieties into crop rotations and their effect on system-level NUE was investigated using a modelling approach.

The modelling component of NUE-CROPS was lead by the University of Copenhagen (Denmark) with partners at Newcastle University (UK), the Chinese Academy of Agricultural Sciences (CAAS), and the Research Institute for Organic Farming (Switzerland).  The subproject drew together results from the four crop-specific workpackages to address gaps in knowledge relating to the impacts of the use of NUE varieties and practices at the rotational and crop production system level. Gaps in knowledge were addressed using both experimental and modelling approaches.

One gap in knowledge concerned the degree of variability in rates of root development and maximum rooting depth among different wheat genotypes. Researchers in Copehagen used mini-rhizotrons inserted into the soil and webcams to document the depth and rate of root penetration (Fig. 1).

Fig. 1. Inserting the mini-rhizotron into the soil (left); diagram illustrating the mini-rhizotron system below-ground (centre); photo of root growth taken from inside the mini-rhizotron (right)

Another knowledge gap concerned the amount of leaf loss by autumn planted oilseed rape during its growing cycle. It was hypothesized that varieties which lose fewer leaves may be more efficient at using applied fertilizer N than those varieties with high rates of leaf loss. Fig. 2 shows the system used to quantify leaf loss for oilseed rape and winter wheat.

Figure 1

Fig. 2. Collection of leaf litter from oilseed rape (left) and winter wheat (right)

Model simulation studies were carried out using the EU-ROTATE-N model where a rotation that consisted of oilseed rape - winter wheat - spring barley - winter wheat - oilseed rape was modelled with varying levels of pre-crop N, soil types, weather, crop phenotypes (root growth, leaf litter, N harvest index) and management (N fertilization, sowing date, cover crops). Full results of this study are available in Dresboll and Thorup-Kristensen (2014).

Further studies were conducted at Newcastle University, where the effects of crop rotation, fertility management, crop protection and variety were studied using the potato year for in-depth analysis (Fig. 3). See Swain et al. (2014) for the results of this study.

Deep Soil Sampling at Nafferton Farm

Fig. 3. Deep Soil Sampling at Newcastle University's Nafferton Farm

Studies in China were conducted at three sites (Ling Xian Station, Dezhou; Yu Cheng Station, Dezhou; Shangdong Agricultural University, Tai An). These studies were focused on identifying the main effects and interactions between fertilizer input types, fertility input levels and wheat and maize varieties on NUE and nitrate leaching (Dezhou sites) as well as water use efficiency at Shandong where trials were conducted in a lysimeter facility.

Fig. 4. Soil water assessment with NMM at the Ling Xian Station.

Fig. 5. The lysimeter facility at Shandong Agricultural University (top) and collecting water samples from the facility (bottom).

The work in China provided definitive evidence that fertilizer inputs and irrigation can be reduced in wheat-maize rotations without significant yield reductions. This has important implications for the future NUE of cropping systems in China.

Finally, researchers in SP5 recommended a hierarchy of actions to improve NUE in cropping systems. These actions were:

  1. Improve crop genetics
  2. Improve crop management e.g. predict N demand, split fertilization etc.
  3. Improve field management i.e. outside the cropping period, by growing cover crops
  4. Improve rotations i.e. look at following crops with poor NUE with those with deep roots that can retrieve deep soil N
  5. Improve off-field measures i.e. drainage water treatment, animal production

Activities in SP5 generated several publications which are listed here:

Dresboll DB, Thorup Kristensen K (2014) Will breeding for nitrogen use efficient crops lead to nitrogen use efficient cropping systems? a simulation study of GxExM interactions. Euphytica 199:97-117

Gu L, Liu T, Zhao J, Dong S, Liu P, Zhang J, Zhao BQ (2014) Nitrate leaching of winter wheat grown in lysimeters as affected by fertilizers and irrigation on the North China Plain. Journal of Integrative Agriculture

Jia X, Peng L (2014) Effect of different nitrogen and irrigation treatments on yield and nitrate leaching of summer maize (Zea mays L.) under lysimeter conditions. Agric Water Manag 137:92-103

Song Z (2014) Long-term effects of mineral versus organic fertilizers on soil labile nitrogen fractions and soil enzyme activities in agricultural soil. Journal of Plant Nutrition and Fertilizer Science 20 (3):525-533

Sun W, Zhao BQ (2013) Effects of nitrogen fertilizer types and input rates on winter wheat quality. Journal of Plant Nutrition and Fertilizer Science 19 (6):1297-1311

Swain E, Rempelos L, Orr CH, Hall G, Chapman R, Almadni M, Stockdale EA, Kidd J, Leifert C, Cooper JM (2014) Optimizing nitrogen use efficiency in wheat and potatoes: interactions between genotypes and agronomic practices. Euphytica 199:119-136

Ytting NK, Andersen SB, Thorup Kristensen K (2014) Using tube rhizotrons to measure variation in depth penetration rate among modern North European winter wheat (Triticum aestivum L.) cultivars. Euphytica 199:233-245