Chemical Fertilizer Reduction and High Yield Cultivation Technique for Peanut

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1. Shandong Peanut Research Institute, Qingdao 266100, China; 2. Gansu Precious Metal Smelting Co., Ltd., Dingxi 730500 China; 3. Weifang Food and Drug Inspection and Testing Center, Weifang 261100, China; 4. Wendeng District Agricultural Technology Extension Station of Weihai City, Weihai 264400, China; 5. Yantai Academy of Agricultural Sciences, Yantai 265500, China

Abstract For a long time, the amount of fertilizer applied to peanuts in China has been much higher than that of other main peanut producing countries. At the same time of increasing production, chemical fertilizers have also brought many adverse effects, which have brought potential threats to the sustainable development of peanut production. While continuously increasing the yield, reducing the amount of chemical fertilizer has become an urgent problem to be solved in peanut production of China. Based on the research results of our team, this paper appropriately absorbed the latest research progress of chemical fertilizer reduction in related fields, and established the cultivation technique for peanut fertilizer reduction and high yield under different cultivation modes, to realize the synchronization of fertilizer reduction and yield increase for peanut production. The technique includes two parts: common technology and different cultivation mode fertilization schemes. The former includes crop rotation, proper deep tillage, application of organic fertilizer, selection of nutrient- efficient varieties, topdressing of foliar fertilizer, etc., the latter includes film mulching spring peanut, continuous cropping field, acidified soil, peanuts interplanting with wheat , and summer direct sowing, etc. This technique provides a technical support for the chemical fertilizer reduction of peanut production in China.

Key words Peanut, Chemical fertilizer reduction, High yield cultivation

1 Introduction

In China, peanut is main oil crop and cash crop. For a long time, in order to obtain higher yield, the amount of chemical fertilizer application for peanut remains high. The recommended application amount of NPK for each 100 kg of pods is about 2.5, 2 and 2.8 kg, respectively[1]. The amount of fertilizer applied per unit is several times or even tens of times that of the main peanut producing countries. Large amount of fertilizer application has played an important role in increasing the peanut yield, but many of the negative effects brought about by chemical fertilizers have become increasingly prominent. Under the precondition of ensuring continuous yield increase, how to reduce the amount of chemical fertilizer has become one of the main tasks of agricultural research and production in China. Since the beginning of 2000, our research team has carried out research on peanut efficient fertilization technology and made great progress. Based on the research results of our team, we appropriately absorbed the latest progress of chemical fertilizer reduction in related fields, and established the cultivation technique for peanut fertilizer reduction and high yield under different cultivation modes. Through field production and application, the amount of NPK fertilizer was reduced by 20%-50%, and peanut yield was increased by 5%-10%. We realized the yield increase and chemical fertilizer reduction at the same time. In this paper, we introduced main points of this technique, in order to provide a technical support for the chemical fertilizer reduction of peanut production in China.

2 Chemical fertilizer reduction and common technology

2.1 Using nutritious and efficient peanut varietiesDifferent genotypes of the same crop have great differences in nutrient absorption capacity and utilization efficiency. According to some studies, the nitrogen utilization efficiency of different types of peanuts differed by 7.6%-8.3%, and the nitrogen fixation rate of Rhizobium differed by 5.0%-23.0%[2]. The difference between nitrogen production efficiency and nitrogen utilization efficiency was 3.7 times and 2.1 times[3], and the phosphorus utilization efficiency differed by 23.1%[4]. Thus, using the nutritious efficient varieties is an effective way to reduce fertilizer for peanut production. At present, our research team has screened out some “double high varieties” with both yield and nutrient efficiency. For example, nitrogen nutrient high- efficiency varieties include Huayu 22, Weihua 8 and so on, phosphorus nutritious efficient varieties include Huayu 36 and Huayu 39, and so on, and high- efficiency varieties of calcium nutrition such as Huayu 32[3-5]. The selection and screening of these "double high varieties" makes it possible to use fertilizer- efficient varieties to achieve chemical fertilizer reduction and high- yield cultivation.

2.2 Crop rotationPeanuts belong to legume crops. Continuous cropping can lead to soil fertility reduction and affect soil continuous fertilization capacity. It is mainly manifested in microbial population imbalance, reduction of related enzyme activity, and stress of phosphorus, potassium, boron, manganese and other elements with relatively high absorption of peanuts. Peanuts rotate with wheat, maize, sweet potato, cotton, vegetables and other non- legume crops for more than one year can not only eliminate the adverse effects of continuous cropping on soil fertility, but also increase peanut yield and benefits.

2.3 Deep tillageDeep tillage can increase the tillage layer, improve soil water storage and soil moisture preservation capacity, promote soil ripening process, accelerate the decomposition and accumulation of soil mineral nutrients and organic nutrients, and improve soil fertility. In addition, the increase of the tillage layer is favorable for the development of peanut roots, expanding the root absorption range, and improving the ability of roots to utilize deep soil nutrients. This can reduce the amount of chemical fertilizer. Generally, deep tillage can be carried out once every 2-3 years, and the depth is preferably 30-35 cm. In the deep tillage year, it is required to pay attention to increasing the application rate of organic fertilizer to accelerate the restoration of soil fertility. Deep tillage can also be carried out with straw returning or using green manure.

2.4 Increasing organic fertilizer or increasing the input of organic materialsOrganic fertilizers not only include a large number of nutrients and trace elements necessary for plants, but also contain rich organic nutrients such as humic acid, vitamins, auxins and organic nitrogen and phosphorus. Besides, organic fertilizers also contain a large amount of organic matters, which has a good regulation effect on soil water, fertilizer, gas and heat. These can provide a good habitat for soil microbial activities, accelerate the mineralization process of organic matter in soil, and enhance soil fertility, and improve the ability of crops to continue to increase the yield. According to some studies, the combined application of organic fertilizer and chemical fertilizer increased the number of bacteria, actinomycetes and fungi in peanut field by 114.9%, 49.0% and 29.0%, respectively, while the activities of urease, sucrase, catalase and acid phosphatase increased by 31%, 27%, 10% and 29%, respectively[6], soil available nitrogen, available phosphorus, and available potassium increased by 17.9%, 23.0% and 12.6%, respectively[7]. Besides, fertilizing the soil is an important way for the continuous high yield of peanuts and the reduction of chemical fertilizers. At present, the organic fertilizers used in production mainly include farmyard manure and commercial organic fertilizer. The farmyard manure mainly includes human waste, barnyard manure, chicken manure, compost, green manure, cake fertilizer, biogas fertilizer and so on. Barnyard manure, chicken manure, and commercial organic fertilizer are most common organic fertilizers. In general, 200-300 kg of manure can be applied for each 100 kg of pods, or 100-150 kg of decomposed chicken manure, or 40-60 kg of commercial organic fertilizer. Stress- resistant peanut in continuous cropping field and acidified soil can properly increase the amount of organic fertilizer. Furthermore, straw returning is also an effective measure to improve soil physical and chemical properties and improve soil continuous fertilization capacity, thus should be vigorously promoted.

2.5 Topdressing of foliar fertilizerTopdressing of foliar fertilizer has the characteristics of fast fertilizer efficiency, low dosage and high utilization rate, especially for medium- and- low- yielding fields. Experiments have shown that a large amount of elements such as NPK and trace elements such as boron, molybdenum and iron can increase yield by 4%-33%[8-10]. The fertilizer utilization rate can reach 2-3 times of conventional root fertilization, and the nitrogen fertilizer utilization rate is up to 80% or more, which is an effective measure for increasing peanut yield and reducing fertilizer. The commonly used foliar fertilizers are mainly urea, calcium superphosphate, potassium dihydrogen phosphate,etc., and the spraying concentrations are 1%, 2% and 0.3%-0.4%, respectively, generally in the late growth stage (late pod stage and pod filling stage). Spraying 2-3 times with interval of 10-15 d can effectively control the premature senescence of the plant, slow down the rate of leaf detachment, increase the photosynthetic potential of peanut growth, and increase the fruit filling rate; the trace elements mainly include borax (or boric acid), ammonium molybdate, ferrous sulfate, zinc sulfate,etc., the spraying concentration was 0.1%-0.2%, and the fertilizer solution dosage was generally 675-750 kg/ha. Boron and molybdenum fertilizers are generally sprayed once in the seedling stage and pegging stage. Iron and zinc fertilizers are generally sprayed when the plants are deficient in sputum, and even sprayed twice, at intervals of about 1 week.

In addition, organic fertilizer can also be applied by base fertilizer, borax (or boric acid) and ammonium molybdate 7.5 kg/ha, and 7.5-15 kg of zinc sulfate per ha. Compound fertilizer can also be applied, the amount being applied as indicated on the product package. Iron fertilizer is generally not used as a base fertilizer. Trace elements do not need to be applied every year, usually once every 2-3 years.

3 Chemical fertilizer reduction technique for peanut production in different cultivation modes

3.1 Types and amount of fertilizers in different cultivation modesThe amount of NPK fertilizers can be determined by soil testing and formula fertilization. If there is no soil testing formula, the NPK formula fertilization method can be used, that is, the amount of NPK accumulated in the production unit weight of pods. The appropriate amount should be determined according to the factors of nitrogen supply, nitrogen, phosphorus and potassium supply capacity, and nutrient efficiency of the varieties. Based on years of research and practice, we believed that the optimum amount of fertilizer applied per 100 kg of peanut pods in Shandong is: 1.0-2.0 kg of pure N, 0.5-1.0 kg of P2O5and 1.5-2.5 kg of K2O. However, the specific amount should be based on the yield level, soil fertility, variety type and planting mode.

3.1.1Film mulching spring peanut cultivation. The fertilization principle for film mulching spring peanut cultivation takes soil to determine the yield, and takes yield as fertilizer, reduce nitrogen and control phosphorus, and slow release nitrogen fertilizer. For the land with medium or higher fertility soil and yield of 4 500 kg/ha, it is recommended to apply 9 000-13 500 kg/ha of barnyard manure, or 4 500-6 750 kg/ha of decomposed chicken manure, or 1 800-2 250 kg/ha of commercial organic fertilizer; 150-225 kg/ha of chemical fertilizer ternary compound fertilizer, 90-120 kg/ha of slow release urea, 135-165 kg/ha of potassium sulfate, or 45-75 kg/ha of diammonium phosphate, 135-165 kg/ha of slow release urea, and 180-225 kg/ha of potassium sulfate. For the land with yield of 6 000 kg/ha, it is recommended to apply 12 000-18 000 kg/ha of barnyard manure, or 6 000-9 000 kg/ha of decomposed chicken manure, or 2 400-3 000 kg/ha of commercial organic fertilizer; 195-300 kg/ha of chemical fertilizer ternary compound fertilizer, 135-165 kg/ha of slow release urea, 180-210 kg/ha of potassium sulfate, or 60-75 kg/ha of diammonium phosphate, 165-225 kg/ha of slow release urea, and 240-330 kg/ha of potassium sulfate. For the land with yield of 7 500 kg/ha, it is recommended to apply 15 000-22 500 kg/ha of barnyard manure, or 7 500-11 250 kg/ha of decomposed chicken manure, or 3 000-3 750 kg/ha of commercial organic fertilizer; 255-375 kg/ha of chemical fertilizer ternary compound fertilizer, 165-210 kg/ha of slow release urea, 225-270 kg/ha of potassium sulfate, or 75-120 kg/ha of diammonium phosphate, 210-285 kg/ha of slow release urea, and 300-375 kg/ha of potassium sulfate. For the land with yield of 9 000 kg/ha, it is recommended to apply 18 000-27 000 kg/ha of barnyard manure, or 9 000-13 500 kg/ha of decomposed chicken manure, or 3 600-4 500 kg/ha of commercial organic fertilizer; 300-450 kg/ha of chemical fertilizer ternary compound fertilizer, 195-240 kg/ha of slow release urea, 270-315 kg/ha of potassium sulfate, or 90-150 kg/ha of diammonium phosphate, 255-330 kg/ha of slow release urea, and 360-450 kg/ha of potassium sulfate. Peanut- specific fertilizers with equivalent nutrient content, or other compound fertilizers, can be applied.

Besides, for the land that is prone to empty shells, calcium fertilizer should be applied. For acidic soil, it is necessary to apply 450-750 kg/ha of lime; for alkaline soil, it is necessary to apply 450-600 kg/ha of gypsum.

3.1.2Yield increase cultivation for peanuts in continuous cropping field. Increasing soil fertility and peanut yield is a primary task for increasing the peanut yield in continuous cropping field. First, it is required to apply organic fertilizers. Organic fertilizer not only contains rich organic matters, but also contains NPK, a variety of medium and trace elements, and has significant effects on improving soil physical and chemical properties, improving soil fertility, and is favorable for enhancing peanut disease resistance and stress resistance. In general, for 1 ha of land, it is proper to apply 15 000-22 500 kg of barnyard manure can be applied, or 7 500 -12 000 kg of decomposed chicken manure, or 3 750 -5 250 kg of commercial organic fertilizer.

Second, it is necessary to increase the biological fertilizers. The imbalance between microbial population and quantity is a main reason for yield reduction of continuous cropping. The biological fertilizer contains a large number of beneficial bacteria, can balance the soil microbial population and quantity, activate the soil mineral nutrient elements, restore soil vitality, and promote peanut growth. There are many types of biological fertilizers (bacterial agents), and the special biological fertilizers for peanuts are preferred. Other beneficial bacterial fertilizers can also be used. The specific amount can be applied according to the recommended amount of the product specification. It is recommended to use biological organic fertilizer, which has the dual effects of organic fertilizer and biological fertilizer, and has a significant effect on relieving obstacles of continuous cropping.

Third, it is recommended to supplement the chemical fertilizers. For 1 ha of land, it is recommended to apply 300-450 kg of chemical fertilizer ternary compound fertilizer, 90-120 kg of slow release urea, 60-105 kg of potassium sulfate, or 75-150 kg of diammonium phosphate.

Fourth, it is necessary to properly apply functional fertilizers. Functional fertilizers not only provide the necessary nutrients for peanut growth and development, but also have many other functions. For example, lime nitrogen can not only provide calcium and nitrogen for peanut growth, but also can disinfect the soil, reduce the amount of harmful organisms in the soil, and reduce the harm of pests to peanuts. Generally, the lime nitrogen is applied together with organic fertilizers before tillage (more than 20 d from sowing), and it is required to take notice of deepening the tillage, the application amount if about 375-450 kg/ha. For the land with application of lime nitrogen, the amount of other nitrogen fertilizers can be appropriately reduced.

3.1.3Yield increase cultivation for peanuts in acidified soil. The physical and chemical properties of acidified soil become deteriorated, which was characterized by soil sticking, caking, soil compaction and poor cultivability. The nutrient elements in the soil are easily leached, the content decreased, and the calcium performance is particularly prominent, resulting in the emptying of peanut pods and the reduction of yield. Besides, the utilization of fertilizer nutrients declines, the fertilization effect is poor; the microbial activity is weakened, the soil enzyme activity is reduced, which influences the activation of mineral nutrition. Fertilization of acidified soil requires the addition of organic fertilizer. Organic fertilizer has a large buffering capacity, which can effectively adjust soil pH and improve soil physical and chemical properties. In addition, it is necessary to supplement the application of calcium fertilizer, the application of alkaline calcium fertilizer such as lime, can not only increase soil calcium nutrient concentration, but also increase soil pH, increase the effectiveness of other nutrients and fertilizer utilization. Furthermore, the balanced application of NPK is needed to meet the normal fertility demands of peanuts. For the land with yield of 4 500 kg/ha, it is recommended to apply 12 000-18 000 kg/ha of barnyard manure, or 6 000-9 000 kg/ha of decomposed chicken manure, or 3 750 -5 250 kg/ha of commercial organic fertilizer; 375-450 kg/ha of chemical fertilizer lime nitrogen, 225-300 kg/ha of calcium magnesium phosphate fertilizer, 180-225 kg/ha of potassium sulfate, or 750-1 200 kg/ha of lime or (or 450-600 kg/ha of silicon- calcium fertilizer), 150-240 kg/ha ternary compound fertilizer, 105-150 kg/ha of urea and 180-225 kg/ha of potassium sulfate. It is prohibited to apply physiological acid fertilizers such as ammonium sulfate and superphosphate to avoid aggravating the soil acidification.

3.1.4Cultivation of peanuts interplanting with wheat and summer direct sowing. Cultivation of peanuts interplanting with wheat and summer direct sowing generally select soil with high fertility, and it is necessary to properly control the fertilizer use. It is recommended to apply 10 500-15 000 kg/ha of barnyard manure, or 4 500-7 500 kg/ha of decomposed chicken manure, or 2 250-3 000 kg/ha of commercial organic fertilizer; 225-300 kg/ha of chemical fertilizer ternary compound fertilizer, 90-150 kg/ha of urea, 150-225 kg/ha of potassium sulfate, or 60-90 kg/ha of diammonium phosphate, 150-210 kg/ha of urea, and 225-300 kg/ha of potassium sulfate.

3.2 Fertilizer application methods

3.2.1Spring sowing plastic- mulching peanuts. Organic fertilizer and 2/3 chemical fertilizer and micro- fertilizer should be applied before tillage, apply 1/3 of the remaining fertilizer before sowing, shallow rotation 15-20 cm, and rotary tillage 2-3 times. It is recommended to achieve leveling, fine soil, and uniform fertilizer, then apply calcium fertilizer (as necessary), and use a peanut combined sowing machine to ridge, sow, spray herbicide, cover film, and press soil, wrap the fertilizer in a solid layer of 0-10 cm, avoiding the high concentration of potassium and calcium in the solid layer and causing rotten pods.

3.2.2Peanuts interplanting with wheat and summer direct sowing. For peanuts interplanting with wheat and summer direct sowing, organic fertilizer and micro- fertilizer should be applied together with wheat base fertilizer. In 15-20 d before interplanting, it is necessary to apply fertilizers in 10-15 cm soil layer through digging ditches. Alternatively, after harvesting the wheat and before flowering of peanuts, apply fertilizers in 5-10 cm soil layer beside the peanut plants, then earth up and water. For summer direct sowing peanuts, apply the nitrogen, phosphorus, and potassium fertilizers after the wheat harvesting and after rotary tillage. For the calcium fertilizer, it is recommended to apply before planting, and wrap the fertilizer in a solid layer of 0-10 cm through the sowing machine.