Study site: The test site is located in the National Field Scientific Observation and Research Station for Grassland Ecology and Hydrology (41°12′10″ N, 111°13′01″ E) in the northern foothills of Yinshan, Halawusu, Damao Banner, Baotou City, Inner Mongolia Autonomous Region, China. This area is characterized by a mid-temperate, semi-arid continental monsoon climate.The zonal soil type of the test site is chestnut, and the soil texture is mostly sandy loam and light loam, with varying degrees of gravelization. With respect to nutrient content, soils are low in nitrogen content, very low in phosphorus content, and high in potassium content.During the experiment (April to September 2020), an ENVIS TrimeLog automatic weather station (produced by German IMKO company) was used to monitor air temperature and humidity, and precipitation. The monitoring results are shown in figure 1.
The experiment was conducted using non-weighing lysimeters constructed with reinforced concrete structures, where the soil was backfilled in layers following construction according to the original soil distribution (Figure 2). The lysimeters were arranged in two rows of 12 (N = 24), with each unit covering an area of 9.9 m2 (4.5 m in length, 2.2 m in width). Each unit was equipped with an independent flow meter and on-off valve to accurately control the irrigation volume. To prevent the interference of natural precipitation, a rain shelter was constructed over the test site consisting of a steel frame covered with transparent panels on the roof ,which was equipped with roller wheels as well as drive units for automated deployment during rainfall.
Study design: Before experimentation, the soil in the lysimeters was sampled using an S-shaped sampling method at depths of 0–15 and 15–30 cm. Samples were transported to the laboratory to determine the following basic physicochemical properties: pH was measured using 0.01 mol·L-1 CaCl2 as the leaching solution, soil organic matter (SOM) was determined using the potassium dichromate oxidation-external heating method 20, soil alkali nitrogen (SAN) was measured using the Conway method 20, soil available phosphorus (SAP) was extracted using sodium bicarbonate and analyzed using Mo–Sb colorimetry 20, and soil available kalium (SAK) was extracted using NH4OAc and analyzed using the flame photometric method 20. Undisturbed soils samples were collected using the ring knife method, and field water holding capacity (FWH) and soil bulk density (SBD) were determined using the constant head method20. The results of the physiochemical parameters measured are shown in Table 1.
Bayou1 naked oats seed (Bayou 1 is a variety of mid maturity and high-quality naked oats developed through interspecific hybridization between skinned oats (Jizhangye 4 as the female parent) and naked oats (8061-14-1 as the male parent) at the Hebei High Cold Crop Research Institute. It was bred through sexual hybridization in 1987 and became a new product of mid maturity and high-quality naked oats) was provided by Research Institute of Pastoral Water Resources Science, Ministry of Water Resources. It is a cultivated genotype, and the collection of plant material complied with the relevant institutional, national, and international guidelines and legislation. A two-factor design was adopted for this experiment. Fertilizer application included two treatments: non-fertilization and the application of basal, starter, and topdressing fertilizers; whereas irrigation quota included four treatments: 750, 1500, 2250, and 3000 m3·ha-1 (N = 8 treatments; Table 2 contains more details on the study design).
In the field fertilization experiment, the soil in the lysimeter was first leveled following deep tilling to 25 cm. As the test site was located in the interlaced area of agriculture and animal husbandry, there were abundant high-quality organic fertilizers (cow and sheep manure). According to the naked oats planting practice of local growers, in this experiment, 15 kg (~15,000 kg·ha-1) of a rotted organic fertilizer was applied at the basal level to the 12 lysimeters in the four fertilization treatments. Naked oat seeds were sown by drill seeding 10 d after fertilizer application. Before sowing, 24 kg of naked oats seeds was mixed with 48 g of 25% azoxystrobin wettable powder (azoxystrobin wettable powder; Jiangsu Dongbao Pesticide Chemical Company; Jiangsu; China) to prevent smut. The seeds were sown at 3 cm depths, with a row spacing of 25 cm, where 1 kg of seeds (100 kg·ha-1) was sown in each unit. Next, 0.15 kg (150 kg·ha-1) of starter fertilizer diammonium phosphate (diammonium phosphate; Jiangsu Dongbao Pesticide Chemical Company; Jiangsu; China) was evenly applied to the 12 corresponding lysimeters, and the soil was then mulched to retain moisture. Topdressing was carried out twice throughout the experimentation process (at jointing period and filling period), during which 0.1 kg (100 kg·ha-1) of urea (urea; Jiangsu Dongbao Pesticide Chemical Company; Jiangsu;China) was evenly applied to the 12 lysimeters.
Irrigation was started at the time of sowing, where the four possible treatment conditions were applied ten times over the five reproductive stages—sowing-seedling emergence, trilobal stage, Jointing stage, heading date, and Grouting period (average of two applications per stage).
Testing methods: naked oats was harvested 140 d after sowing, and the following indicators were measured and assayed:
Aboveground fresh weight: Five 1-m2 naked oats plots were randomly selected for harvesting. The fresh weight of the aboveground biomass was determined, and the yield per hectare was calculated.
Plant height , basal stem diameter, number of spikes, and number of grains per ear: Five naked oats plants were randomly selected in the sample plots to measure plant height using a tape and the basal stem diameter using Vernier caliper.Use counting method to calculate the number of spikes, grains per ear of naked oat.
naked oats seed weight: The fresh weight of the naked oats seeds was measured, and then they were placed in an oven and dried at 60 °C for 12 h. After drying, count 1000 seeds and measure their weight with a analytical balances(analytical balances(FA2204N);JOANLAB company;Zhejiang;China).
Protein: The protein content in naked oats seeds was determined using the Kjeldahl method 20.
Lipid: The lipid content in naked oats seeds was determined via Soxhlet extraction 20.
crude fiber:The crude fiber content in naked oats seeds was determined a fixed amount of acid and alkali under specific digestion conditions, with ether degreasing and ethanol removal of alcohol-soluble substances and high temperature scorching. The mass of minerals was deducted and the remaining amount was considered as crude fiber.
starch :starch content in naked oats seeds was determined enzymatic hydrolysis method 20.
amino acids:The amino acids content in naked oats seeds was determined using the L-8900 amino acid analyzer manufactured by Hitachi Group, Japan. Due to the differences in acidity, polarity and molecular size of different amino acids, the adsorption capacities of different amino acids to cation exchange resin in different pH environments were also different; the equipment used these characteristics. First, the pH of amino acid samples was adjusted to 2.2, such that all amino acids were adsorbed by the cation exchange resin. As the buffer flowed through the exchange column and the pH of the mobile phase was increased, the positive charge of amino acids was reduced and some amino acids were eluted. The contents of various amino acids in the sample were calculated from the areas of different elution peaks.
Statistical analysis: Graphs were plotted using Origin 2018 SR1 (OriginLab Corporation, Northampton, MA, USA), and statistical analyses were carried out using SPSS v.23.0 (SPSS Inc., Chicago, IL, USA). One-way analysis of variance (ANOVA) was performed to test for significant effects of fertilizer application and irrigation quota on the naked oats growth (seed yield, thousand seed weight, number of spikes, number of grains per ear, plant height, and basal stem), and nutrient content (protein, lipid,crude fibre and starch). Two-way ANOVA was performed to test for significance regarding the effects of fertilizer application and irrigation quota on aboveground and naked oats seed biomass, as well as protein and lipid contents. To compare the least significant difference and priming effect at a significance level of 0.05, we performed multiple comparisons using Duncan's test.