Effects of Nitrogen Fertilizer Regulation with Straw-return on Wheat Yield and Different Forms of Potassium in the Soil

Liang DONG, Zeqiang SUN, Xuejun WANG, Xiaoxia DONG, Honghai GUO, Dongfeng ZHENG,Zheng MA

Institute of Agricultural Resources and Environment, Shandong Academy of Agricultural Sciences/Scientific Observing and Experimental Station of Arable Land Conservation (Shandong), Ministry of Agriculture/Key Laboratory of Agro-environment in Huanghuaihai Plain, Ministry of Agriculture/Shandong Provincial Key Laboratory of Plant Nutrition and Fertilizer, Ji’nan 250100, China

Potassium (K) is a necessary nutrient element for plant growth. With the continuous increase of crop yield,nitrogen(N)and phosphorus(P)dosages,the absorbed K content of crops from soil has gradually increased,thereby soil K has been of deficit gradually[1]. However, K resource in China is scarce, in face of the increasingly serious K deficiency in the soil , it is urgently needed to seek an effective supplementary means for soil K except chemical K[2]. Crop straw is a precious and ubiquitous natural organic material, its K content is very rich. As the major grain producing area, the Huang-Huai-Hai Plain has abundant straw resources, thus straw returned to the field directly or indi rectly can construct a good soil ecosystem[3], and is also an important measure to improve the basic fertility of farmland soil. Some studies have found that straw-return can increase organic content in the soil,change soil structure, increase crop yield and improve the utilization efficiency of chemical fertilizers, especially N fertilizer[4].In the condition of straw-return, rationally arranging N fertilizer applicationcan improve wheat yield[5].At present,many studies on the effects of N fertilizer dosage,crop yield,and soil physical and chemical properties in the condition of straw-return have been carried out[6-7],however,the studies on the change of K forms and K balance between crop and soil in the condition of straw-return have been few.

Winter wheat is the main grain crop for North China. To obtain considerable yield, excessive water and fertilizer resources have been input,moreover, its utilization rate has been low[8].With the adjustment of Chinese agricultural structure, fertilizer utilization would be further improved. In this paper, under the wheat—maize rotation system of one-year two-harvest cultivation in Huimin County of Binzhou City, the effects of N fertilizer regulation with straw-return on crop yield and soil K forms were studied,so as to provide a scientific basis for nutrient management in the condition of cyclic utilization of straw in the wheat—maize rotation system of the Huang-Huai-Hai Plain.

Materials and Methods

Experimental materials

Experimental fertilizers Urea and calcium superphosphate were the experimental fertilizers, in which urea contained 46% N, and calcium superphosphate contained 16%P2O5.

Experimental crop Winter wheat with the variety of Weimai No.8, which bred by Weifang Academy of Agricultural Sciences,was chosen as the experimental crop.

Experimental soil The experimental soil was moisture soil,its basic physicochemical properties were: pH 8.0,1.1% organic matter, 45.2 mg/kg available N,38.9 mg/kg rapid available P, 2.3 mg/kg water-soluble K, 49.1 mg/kg exchangeable K, 142.3 mg/kg non-exchangeable K and 1.21% total K.

Experimental design

There were 8 treatments for the experiment, and each treatment had three repetitions. All treatments had the same dosage of P fertilizer and no K fertilizer;the control group (CK)had no N fertilizer, and all the other treatments had the same N fertilizer application. The dosages of N, P2O5and K2O were 225, 90 and 0 kg/hm2, respectively. The concrete contents of the experiment were shown in Table 1.

The experiment was carried out in Lidong Village, Li Town, Zao Household of Huimin County. In October of 2012, after harvesting, maize straw was all crushed and returned to the field,N fertilizer applied as base fertilizer was dissolved in water and sprayed on the maize straw; on October 5 of 2012, plowing the field and sowing the wheat seeds were carried out, the daily management was based on local farmers’custom.

Table 1 Experimental design

Measuring items and methods

On June 15 of 2013, the wheat was harvested, the yield of 4 m2of each plot was calculated to reckon the yield.

Water-soluble K was extracted using distilled water with 10 ∶1 ratio of water to soil,exchangeable K was extracted using 0.5 mol/L neutral ammonium acetate solution, exchangeable K = extracting K by ammonium acetate-water-soluble K; non-exchangeable K was extracted by the heating of 1 mol/L salpeter solution, non-exchangeable K = digesting K by nitric acid - extracting K by ammonium acetate; total K was fused using sodium hydroxide[9].K content was measured by atomic absorption spectrophotometer.

Data processing and analysis

Statistic analysis of data was carried out using DPS software[10], Duncan’s new multiple range method was carried out for multiple comparisons.

Results and Analyses

Effects of N fertilizer regulation with straw-return on wheat yield and 1 000-seed weight

As shown in Table 2, on wheat yield, compared with CK, wheat yields under the treatments of conventional fertilization, the ratio of basal to topdressed nitrogen of 10 ∶0, the ratio of basal to topdressed nitrogen of 7 ∶3,the ratio of basal to topdressed nitrogen of 6 ∶4, the ratio of basal to topdressed nitrogen of 5 ∶5, the ratio of basal to topdressed nitrogen of 4 ∶6 and the ratio of basal to topdressed nitrogen of 3∶7 respectively increased by 3.60%,4.80%,5.54%,5.49%,3.91%,4.20% and 3.53% . These indicated that no N fertilizer affected wheat yield,moreover, the differences between no N fertilizer treatment and all the other treatments were significant.Compared with conventional fertilization, the treatments of the ratio of basal to topdressed nitrogen of 10 ∶0, the ratio of basal to topdressed nitrogen of 7 ∶3,the ratio of basal to topdressed nitrogen of 6 ∶4, the ratio of basal to topdressed nitrogen of 5∶5 and the ratio of basal to topdressed nitrogen of 4∶6 respectively increased by 1.16%,1.87%,1.83%, 0.30% and 0.58%, however,wheat yield under the treatment of the ratio of basal to topdressed nitrogen of 3 ∶7 decreased by 0.07%, indicating that N deficiency at the early growth stage of wheat affected the yield.Hereinto, wheat yield was the highest under the treatments with the ratios of basal to topdressed nitrogen of 7 ∶3 and 6 ∶4, and the difference between the two was not significant.

As shown in Table 2, on 1 000-seed weight,compared with CK,1 000-seed weights under the treatments of conventional fertilization, the ratio of basal to topdressed nitrogen of 10 ∶0,the ratio of basal to topdressed nitrogen of 7 ∶3, the ratio of basal to topdressed nitrogen of 6 ∶4, the ratio of basal to topdressed nitrogen of 5 ∶5,the ratio of basal to topdressed nitrogen of 4 ∶6 and the ratio of basal to topdressed nitrogen of 3∶7 respectively increased by 0.53%, 1.06%, 1.58%,3.96% , 1.85% , 2.64% and 2.64% .These showed that no N fertilizer during the growth period of wheat affected the supply of N, thereby affecting 1 000-seed weight of wheat, moreover,the differences between no N fertilizer treatment and all the other treatments were significant.Compared with conventional fertilization, the treatments of the ratio of basal to topdressed nitrogen of 10 ∶0, the ratio of basal to topdressed nitrogen of 7 ∶3,the ratio of basal to topdressed nitrogen of 6 ∶4, the ratio of basal to topdressed nitrogen of 5 ∶5, the ratio of basal to topdressed nitrogen of 4 ∶6 and the ratio of basal to topdressed nitrogen of 3∶7 respectively increased by 0.52%, 1.05%, 3.41%, 1.31%, 2.10%and 2.10%. These indicated that the fertilizing method of conventional fertilization was also bad for improving the 1 000-seed weight of wheat.Hereinto, the 1 000-seed weight of wheat was the highest under the treatment with the ratio of basal to topdressed nitrogen of 6∶4.

Table 2 Effects of N fertilizer regulation with straw-return on wheat yield and 1 000-seed weight

Effects of N fertilizer regulation with straw-return on the contents of different forms of K and the corresponding proportions

The content of total K in the soil Seen from Fig.1, it was drawn that different regulation proportions of N fertilizer under straw-return would have effects on the content of total K in the soil.The contents of total K in the soil under the treatments of the ratios of basal to topdressed nitrogen of 10 ∶0,7∶3 and 6 ∶4 were higher, specifically,the larger the proportion of basal N fertilizer, the higher the content of total K in the soil.Different soil layers also had different contents of total K, generally,the content of total K in the soil layer of 20-40 cm was higher than that of 0-20 cm soil layer.

The contents of water-soluble K in different soil layers and the corresponding proportions Water-soluble K refers to the K which exists in the soil solution with the form of potassium ion (K+),it can be absorbed and used directly by crops[11]. As shown in Table 3, the contents of water-soluble K in the soil layers of 0-20 and 20-40 cm were lower, and the proportion of which in total K was also lower. In the condition of straw-return, the contents of water-soluble K in the soil layers of 0-20 and 20-40 cm under the treatments of the ratios of basal to topdressed nitrogen of 7∶3 and 6∶4 were the highest, indicating that increasing basal N fertilizer was beneficial to im-proving water-soluble K content in the soil. The reason may be: after the straw-return, N fertilizer application was more,the rate of straw decay became quicker,thus more K entered into the soil, thereby the content of K in the soil was increased. Hereinto, the content of water-soluble K in the soil layer of 0-20 cm under the treatment of the ratio of basal to topdressed nitrogen of 7∶3 was the highest.

Table 3 Effects of N fertilizer regulation with straw-return on the contents of water-soluble K in different soil layers and the corresponding proportions

Table 4 Effects of N fertilizer regulation with straw-return on the contents of exchangeable K in different soil layers and the corresponding proportions

Table 5 Effects of N fertilizer regulation with straw-return on the contents of non-exchangeable K in different soil layers and the corresponding proportions

The contents of exchangeable K in different soil layers and the corresponding proportions Exchangeable K refers to the K+which absorbs on the surface of soil colloid,as well as the K+which is absorbed by negative charge of soil colloid and can be exchanged by neutral salt,it is an important part of soil available potassium[11].

As seen in Table 4, in the condition of straw-return, the contents of exchangeable K in the soil layer of 0-20 cm under the treatments of the ratios of basal to topdressed nitrogen of 10 ∶0, 7 ∶3 and 6 ∶4 were higher, and those in the soil layer of 20-40 cm under the treatments of the ratios of basal to topdressed nitrogen of 7 ∶3 and 6∶4 were the highest,showing that basal N fertilizer was sprayed on the straw,with the increase of basal N fertilizer application for wheat,the degree of straw decay increased, thereby the content of exchangeable K in the soil was increased.In addition,the proportion of exchangeable K content in total K under the treatments of the ratios of basal to topdressed nitrogen of 7 ∶3 and 6∶4 was higher. Different soil layers also had different contents of exchangeable K, generally, the content of exchangeable K in the soil layer of 0-20 cm was higher than that of 20-40 cm soil layer.

The contents of non-exchangeable K in different soil layers and the corresponding proportions Nonexchangeable K refers to the K which exists in the layers of layer silicate mineral and the margin of particles,and can not be extracted by neutral salt in a short time, it is also called slowly available K. Non-exchangeable K is the reserve library of rapidly available K, when the concentration of rapidly available K declines because of the absorption of crops and leaching loss, some non-exchangeable K will be released and transformed as exchangeable K and water-soluble K,thereby becoming rapidly available K for crops[11].

As demonstrated in Table 5,in the condition of straw-return, the variation range of the contents of non-exchangeable K in the soil under different ratios of basal to topdressed nitrogen was small. And the contents of non-exchangeable K in different soil layers also had not obvious difference.These showed that the contents of non-exchangeable K under straw-return and N fertilizer regulation had not obvious change in the one-season experiment contion.

Conclusions and Discussions

Straw-return is the main way for the reuse of straw resource as agricultural waste at present[12]. Strawreturn can regulate soil physical environment, promote metabolic activity of environmental microorganism, benefit the transfomation of soil nutrient and increase organic content in the soil.Straw, as an important resource containing rich K,is of great importance in alleviating the scarcity of potassium mineral resources in China and seeking K fertilizer substitute to continuously supplement soil K[1,13].

In the experiment, from the aspects of wheat yield and different forms of K in the soil,N fertilizer regu-lation with straw-return can affect wheat yield and the contents of watersoluble K and exchangeable K. The treatment effect of the ratios of basal to topdressed nitrogen of 7∶3 and 6∶4 was better, such as the corresponding wheat yields were the highest and respectively reached 5 621.1 and 5 618.6 kg/hm2, the contents of watersoluble K and exchangeable K were also the highest, moreover, total K content in the soil was also the highest. These indicated that in the condition of straw-return, appropriately increasing N fertilizer input at the earlier stage was beneficial to the growth of wheat and the improvement of soil available K content, thereby providing more K element for the direct absorption and utilization of crops.Increasing N fertilizer at the earlier stage had some differences with the conventional N fertilizer postponing theory proposed by Chen Xiang et al.[14]and the theory of“regarding basal fertilizer and despising topdressed fertilizer” put forward by Zhou Haiyan et al.[15], the reasons may be: the experiment was carried out in the condition of straw-return, basal N fertilizer not only promoted the growth of crops,but also played the role of regulating C/N ratio of maize straw and promoting the effect of straw decay,thereby playing the fertility role of straw-return to the greatest extent.In the experiment,before 2012,there was always straw-return and N fertilizer spreading over the fields,since October of 2012,basal N fertilizer has been dissolved in water and has sprayed on the straw, which replaced the traditional farm operation of spreading fertilizer over the fields,therefore, it had greater promoting effect on rapid decomposition of straw.

At present, under the support of the policy of popularizing straw-return nationwide,it is suggested that N fertilizer input at the earlier stage should be increased properly,which has good effect for promoting soil fertility under agricultural output and straw-return.From the angle of saving resource,how much K fertilizer can be replaced by straw-return, and how much straw should be returned for having no influence on crop seedlings and having fertilizer effect, still need to be studied and discussed.The effect of straw-return on soil fertility is the result of combined action of soil types, climate and tillage management[16], its effect has time accumulation, so it needs to be tested chronically, continuously monitoring the key factors of cropsoil-atmosphere (precipitation) can scientifically ensure the effect of straw-return.

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