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Cereal crop Zn biofortification is an effective solution to global human Zn deficiency and is achieved by increasing grain Zn concentration concurrently with yield. However, the desired grain Zn concentration (>40 mg kg−1) is rarely observed for high-yielding wheat on calcareous soils, owing to inadequate Zn uptake or Zn distribution to grain. This study was designed to determine how much Zn uptake or distribution is adequate for Zn biofortification, by considering 123 bread wheat (Triticum aestivum L.) cultivars grown on calcareous soils with low available Zn (

High crop yield and high quality are the primarily targets in intensive crop production. Although the plastic film mulch (PFM) approach has been well established for high-yielding wheat production in dryland, effects of PFM on wheat grain quality is still poorly understood. Therefore, multi–site and fixed location field experiments were conducted to investigate effects of PFM on grain yield, protein content and its components content of dryland winter wheat in 2014–2016 in the Loess Plateau of China. Compared with no mulch (NM), PFM increased the grain yield, structural protein contents and the ratio of gliadin/glutenin by 634 kg ha−1, 11.3%–30.8% and 15.1%, respectively, but reduced the total protein and its gluten contents by 7.8% and 3.4%–15.1%. Furthermore, PFM significantly increased the proportion of albumin, globulin and gliadin to total protein by 22.3%, 44.2% and 5.5%, respectively, but decreased the proportion of glutenin by 7.4%, compared to NM. The highest grain yield, albumin and glutenin content were attained when the critical N rates were 146 kg N ha−1, 167 kg N ha−1 and 100 kg N ha−1, respectively. Moreover, for every 100 kg ha−1 increase in N fertilizer, the globulin content increased by 0.11%, but the ratio of gliadin/glutenin decreased by 0.12%. In summary, PFM did not show any benefit for gluten, while precise N fertilizer management provided an opportunity for improving grain processing quality of dryland wheat. In order to tradeoff between grain yield and its processing quality, the optimal N application rate (146–167 kg N ha−1) should be considered under PFM. These findings suggest that optimal N management serves as a basis for further investigation and regulation of grain protein components of wheat under PFM in the semiarid area of China and similar cropping system around the world.

The solution to address global human Zn deficiency is Zn biofortification of staple food crops, aimed at high grain Zn concentration as well as high yield. However, the desired high grain Zn concentration above 40 mg kg-1 is rarely observed for high-yield wheat on worldwide calcareous soils, due to inadequate Zn uptake or Zn distribution to grain. The present study aims to investigate how much Zn uptake or distribution is adequate to achieve the Zn.t of high-yield wheat on calcareous soils with low available Zn (∼ 0.5 mg kg-1). Of the 123 cultivars tested in a three-year field experiment, 19 high-yield cultivars were identified with similar yields around 7.0 t ha-1 and various grain Zn concentrations from 9.3 to 26.7 mg kg-1. The adequate Zn distribution to grain was defined from the view of Zn biofortification, as the situation where the Zn distribution to grain (Zn harvest index) increased to the observed maximum of ∼ 91.0% and the Zn concentration of vegetative parts (straw Zn concentration) decreased to the observed minimum of ∼ 1.5 mg kg-1 (Zn.m). Under the assumed condition of adequate Zn distribution to grain (∼ 91.0%), all the extra Zn above Zn.m was remobilized from straw to grain and the grain Zn concentration would be increased to its highest attainable level, which was 14.5 ∼ 31.3 mg kg-1 for the 19 high-yield cultivars but still lower than 40 mg kg-1. Thus, even with the adequate Zn distribution to grain, the current Zn uptake is still not adequate and needs to be increased to 308 g ha-1 or higher to achieve Zn.t for high-yield wheat (7.0 t ha-1) on low-Zn calcareous soils. Besides, the established method here can also provide the priority measures and quantitative guidelines to achieve Zn biofortification in other wheat production regions.

The most effective measure to address human zinc (Zn) deficiency worldwide is genetic Zn biofortification of cereal grains, namely breeding crop cultivars with both high yield and high grain Zn concentration. This has been not easy due to the widely reported yield dilution effect on grain Zn, while the Zn uptake and its distribution, as sources for grain Zn filling, were much less investigated for overcoming the yield dilution. A field study was conducted in a calcareous low-Zn soil in dryland with 123 modern wheat cultivars planted for two years, and different traits were determined at maturity to characterize cultivars with high or low grain Zn at the same yield levels. For all tested cultivars, grain Zn concentration showed no significant correlation with yield in both years. Then 19 cultivars were identified with consistent yield and grain Zn performances across years, and classified into four groups: low-Zn low-yield (n = 4), high-Zn low-yield (n = 4), low-Zn high-yield (n = 7), and high-Zn high-yield (n = 4). For low-yield cultivars, grain Zn was more closely related to shoot Zn uptake, while for high-yield cultivars, both shoot Zn uptake and Zn harvest index were closely related to grain Zn. From the seven high-yield low-Zn (7142 kg ha−1, 14.7 mg kg−1) to the four high-yield high-Zn cultivars (7287 kg ha−1, 20.8 mg kg−1), there was no yield dilution effect on grain Zn because the latter possessed both high shoot Zn uptake (190 g Zn ha−1) and high Zn harvest index (79%). In conclusion, yield dilution is not necessarily an obstacle for increasing wheat grain Zn concentration. Enhancing the Zn uptake and its distribution to grain make it possible to achieve high grain Zn and high yield simultaneously, promoting the success of genetic Zn biofortification for dryland wheat.

Plastic film mulch has been proved of great potential to enhance crop productivities in drylands, but there is still lacking insight into its underlying changes in crop grain nutritional quality. Therefore, field experiments were conducted to investigate the effects of different soil surface managements on grain yield and its protein content of winter wheat in 2014–2016 at different fertilizer input levels under no mulch and plastic film mulch at seven sites in dryland of the Loess Plateau in northwest China. Compared with no mulch, overall average grain yield was significantly increased by 13.7%, but its protein content was decreased by 7.8% with plastic film mulch. Apart from the dilution effects caused by the much more increase of grain yield, the decreased N remobilization from vegetative parts to grain and the lowered crop N uptake from soil during grain filling stage were found to be the main reasons, when the overall average of N remobilization efficiency, N harvest index and post-anthesis N uptake was respectively decreased by 16.0%, 5.7% and 24.0%. However, the winter wheat grain protein content was observed to increase more quickly with the N rate increase under plastic film mulch, compared to no mulch. This provides opportunity to increase the grain protein content under plastic film mulch to the same level of no mulch by increasing the N fertilizer application rates, and an estimation of optimal N application rates for winter wheat grain yield and its protein content was computed under plastic film mulch in drylands.

The excessive application of fertilizer can inhibit the crop yield and decrease the nutrient use efficiency, as well as leading to nitrate-N residues in soils and other economic and environmental issues. In this study, an optimized method for fertilizer recommendation was developed based on soil testing at harvest of the previous crop. Multi-site and fixed location field experiments were conducted to assess this method from 2013 to 2016 in the typical dryland winter wheat (Triticum aestivum L.) production area of the Loess Plateau in China. Compared with the conventional fertilizer application (CFA), optimized fertilizer application (OFA) decreased the fertilizer application rates by 96 kg N ha−1 and 43 kg P2O5 ha−1, and the nitrate-N residues by 120 kg N ha−1 in the 0–100 cm soil layer, as well as increasing the winter wheat grain yield by 386 kg ha−1 and the economic returns by $ 230 ha−1 averaged across sites and years. Furthermore, the OFA method caused no changes in nitrogen (N), phosphorus (P), and potassium (K) uptake in wheat compared with CFA, but increased the harvest index by 4%, 3%, and 7% for N, P, and K, respectively. Averaged across years and sites, compared with CFA, the internal efficiency rate of N, P, and K under OFA were increased by 9%, 4%, and 8%, respectively, and the corresponding partial factor productivity for these nutrients also increased by 85%, 61%, and 31%. Thus, soil testing at harvest and determining fertilizer recommendations according to the proposed OFA method can decrease the fertilizer rates, as well as achieving a balance among the conflicting aims of environmental protection, crop yield increases, nutrient use efficiency, and improved economic benefits in dryland farming areas where the over-application of fertilizers occurs.

Zinc (Zn) biofortification of staple food crops is essential for addressing worldwide human malnutrition problem, but its success has been restricted by low soil Zn availability. With ethylenediaminetetraacetic acid (EDTA) addition, soil Zn availability is able to be increased in contaminated soils, but whether and how it will behave in uncontaminated calcareous soil with low available Zn, and its effect on winter wheat grain Zn need further research. In a series of pot experiments, winter wheat was grown on a low-Zn calcareous soil, with EDTA applied at different stages or in different rates, and then soil pH, soil available Zn, Zn fractions, and Zn concentration of different wheat organs were determined. Obtained results showed that grain Zn concentration was increased by 8%–46%, but grain yield was not affected by EDTA addition. With EDTA applied at sowing, straw Zn uptake was increased by 69%–120% during heading to filling, and after anthesis it significantly decreased and contributed 61% of the grain Zn uptake. Meanwhile, soil available Zn (DTPA-Zn) in rhizosphere and nonrhizosphere was increased by 185%–377%. Correspondingly, soil exchangeable Zn (Ex-Zn) was dramatically increased; Zn weakly bounded with organic matter (Wbo-Zn) and Zn bounded with carbonate (Carb-Zn) were increased by 4%–54% and 2–18 fold respectively; while Zn bounded with amorphous iron oxide (AmoFe-Zn), Zn bounded with crystal iron oxide (CryFe-Zn), and Zn in residue mineral (Res-Zn) were decreased by 78%, 10%–31%, and 6% respectively, and soil pH kept stable or increased by 0.1–0.2 unit. Among Zn fractions only Ex-Zn, Wbo-Zn, and Carb-Zn were significantly and positively correlated with DTPA-Zn. With EDTA application, the enhanced soil Zn transformation from unavailable Zn fractions (AmoFe, Cry-Fe, and Res) to available Zn fractions (Ex, Wbo, Carb), and the enhanced straw Zn uptake at anthesis and its remobilization to grain during filling period was responsible for the increase of grain Zn concentration. Also, without decreasing soil pH the unavailable soil Zn fractions can be still transformed to available Zn in calcareous soil.

Over-fertilization is economically and environmentally undesirable, and under-fertilization contributes to yield gaps. In dryland cropping systems, where precipitation is a major source of variation in yield, matching fertilizer to precipitation is critical. The aim of this study was to outline and test a method to match nitrogen (N), phosphorus (P), and potassium (K) fertilizer rate to precipitation for dryland winter wheat in the Loess Plateau of China. Based on field experiments at 52 sites from 2009 to 2013, the grain yield of winter wheat was found to increase quadratically with the precipitation in two periods: summer fallow, and summer fallow until jointing stage. The shoot N, P, and K nutrient uptake were linearly correlated with grain yield. Basal fertilizer requirement was calculated from target grain yield estimated as a function of fallow precipitation. The need for topdressing was determined by re-estimating target grain yield as a function of precipitation during summer fallow until jointing stage. Validation of this method using an additional dataset from long term studies in the same area suggested that adjusting fertilizer rates to summer fallow and summer fallow until jointing precipitation could correct the over application for N and P fertilizer, and deficient application for K fertilizer in the Loess Plateau.

Plastic film mulching systems are widely used in crop production because of great benefits in increasing crop yields, but transparent film mulching (TFM) has negative impacts on crop production due to the high soil temperature under certain conditions. Because of its lower impacts on soil temperature, black film mulching (BFM) is being considered as an alternative to TFM. A meta-analysis was therefore conducted to compare the benefits and trade-offs of TFM and BFM use in potato, maize, and wheat production. Overall, the plant height, aboveground biomass, water use efficiency, and yield under plastic film mulching increased by 7–17 %, 27–59 %, 20–47 %, and 17–35 %, respectively. However, film mulching shortened the crop phenology by 4–9 % due to the higher soil temperature compared with non-mulching. Compared with TFM, the mean soil temperature over the crop growing season under BFM reduced by 1.1 °C, which resulted in a 3–5 % increase in phenology. This is a crucial factor for BFM to increase maize yield by 6% and improve marketable tuber rate of potato by 9%, which led to higher profits, compared with TFM. In addition, no herbicide was used in BFM system, thereby eliminating the costs of herbicide and its application. As a result, the net economic benefits in BFM were 5–11 % higher than those in TFM for crop production. In conclusion, the BFM system leads to greater crop growth and higher economic benefits than the TFM system, especially for maize and potato. Policies and investment incentives that support the promotion of BFM technology should be prioritized in order to pursue these greater benefits.

Soil nitrate–N residue after harvesting crops and nitrate–N loss during the following fallow season is serious concern for the agricultural environment in dryland. A 6-year-long, location-fixed field experiment was conducted to determine the effects of plastic film mulch (PM), straw mulch (SM), green manure (GM) and straw mulch plus green manure (SGM) on the nitrate–N residue, loss and accumulation in a winter wheat-summer fallow system. Compared with the bare fallow, average grain yield was increased by 6 % with PM, whereas decreased by 7, 5 and 5 % with SM, GM and SGM, respectively. Average total N uptake was decreased by 13 % with SM, but not affected by PM, GM and SGM. Average nitrate–N residue at wheat harvest was decreased by 35, 32 and 18 % with PM, SM and SGM, respectively, but not affected by GM. Average soil water recharge was increased by 12 % with PM, and not affected by SM, whereas decreased by 20 and 16 % with GM and SGM, respectively. For the PM, SM, GM and SGM, the average nitrate–N loss from top soil was decreased by 51, 53, 50 and 34 %, respectively, and the average nitrate–N accumulation in deep soil was decreased by 56, 45, 31 and 39 %. Above results revealed that increasing the yield decreased soil nitrate–N residue, and nitrate–N loss and accumulation was restricted by the decreased nitrate–N residue and soil water recharge. Overall, PM is a preferable measure for the decreased nitrate–N residue, loss and accumulation, at the same time increased the yield in dryland.

Nitrate-N residue (NR) in soil is attracting increasing attention because of its environmental risks. However, research information to regulate NR in soil by optimizing chemical nitrogen (N) fertilizer input and at the same time ensuring a satisfactory high grain yield is still lacking, particularly in the drylands of northwestern China. A 9-yr field experiment was initiated in 2004 in the Loess Plateau of China to investigate the dominant factors affecting NR in soil at harvest and optimize the N input for winter wheat by balancing the grain yield and NR in soil. Obtained results showed that varied grain yields and N application rates resulted in different NR in soil in dryland. The NR increased quadratically with the N rates, and the average NR was 59.0, 98.7, 175.1, 326.0, and 475.5 kg N ha−1 in 0–300 cm soil, respectively, at N rates of 0, 80, 160, 240, and 320 kg N ha−1, of which 35.1, 54.5, 94.5, 186.5, and 222.0 kg N ha−1 was in the 0–100 cm soil. Seasonal N residue (SNR) in soil also increased quadratically with N rate, with the yearly increases correspondingly being 0, 4.4, 8.8, 13.2, and 17.7 kg N ha−1. The fertilizer N residue (FNR) increased linearly with N rate, with the yearly FNR increases, respectively, to be 0.02, 7.1, 14.1, and 21.1 kg N ha−1 at N rates of 80, 160, 240, and 320 kg N ha−1. The seasonal nitrate-N residual depth (NRD) was mainly within the 0–100 cm soil layer. The NR, SNR, FNR and NRD were all affected by but not correlated with precipitation. In the experimental site, the NR was able to be slowly leached downward to deeper soil by 13.3–33.3 cm each year driven by precipitation. The findings suggest that if the NR is to be decreased to 55–67 kg N ha−1 in the 0–100 cm soil while maintaining a relatively high grain yield (4487–5000 kg ha−1), an N application rate of 66–92 kg N ha−1 should be recommended.

Nitrogen (N) fertilizer application is an essential way to keep the high yielding crop production, but nitrate-N residue in agricultural soils has attracted wide attentions due to its various environmental effects. Understanding the yield formation and its relation to the N uptake and requirement are urgently needed to reduce the nitrate-N residue for plastic mulched wheat production in drylands. A three-year location-fixed field experiment with five N rates was carried out to test the grain yield formation and N use characteristics of wheat and soil nitrate-N response to no mulch (NM) and plastic film mulch (PM) cultivations. Obtained results showed that the PM promoted the wheat growth and had higher maximum grain yield and biomass at the similar N rate, compared to the NM. Although wheat took up much more N from the soils under the PM, its N requirement for 1000 kg grain formation (NR) showed no significant difference from that of the NM, and for management of N fertilization, the same NR can be used for both cultivations in dryland. Nitrate-N content in 0–20 cm top soil (SNC) was found lower under NM than that under PM, but nitrate-N residue in 0–100 cm soil (SNR) showed no significant difference between these two cultivations. The SNR was significantly and linearly correlated with the SNC under both cultivations, and thus the SNC is able to be used to predict the SNR. Therefore, the present work provides a feasible way or an idea to use the top soil nitrate content, wheat grain yield and its N requirement to optimize the N application rates and N fertilizer recommendation for wheat production and soil nitrate-N residue control in dryland.