Effects of different mechanized soil fertilization methods on corn soil fertility under continuous cropping

Experiments for mechanized soil fertilization for corns were conducted in Faku demonstration zone. On this basis, we studied effects on corn soil fertility under continuous cropping due to different mechanized soil fertilization methods. Our study would serve as a theoretical basis further for mechanized soil fertilization improvement and soil quality improvement in brown soil area. Based on the survey of soil physical characteristics during different corn growth periods, we collected soil samples from different corn growth periods to determine and make statistical analysis accordingly. Stalk returning to field with deep tillage proved to be the most effective on available nutrient improvement for arable soil in the demonstration zone. Different mechanized soil fertilization methods were remarkably effective on total phosphorus improvement for arable soil in the demonstration zone, while less effective on total nitrogen or total potassium, and not so effective on C/N ratio in soil. Stalk returning with deep tillage was more favorable to improve content of organic matter in soil, when compared with surface application, and organic granular fertilizer more favorable when compared with decomposed cow dung for such a purpose, too.


Introduction
Since soil is the material basis of crop production, soil fertility magnitude will determine crop growth and yield. Organic fertilizer applied in agricultural production plays its roles mainly in soil improvement, fertilization betterment, and yield gain and quality improvement. Different tillage methods and soil fertilization methods both would affect soil fertility greatly. Mechanized fertilization worked nine times faster than traditional fertilization, so it was able to save labor resource, and both were not so significantly different in terms of greenhouse gas emission [1]. Therefore, mechanized fertilization is of higher promotional value in a way. Stalk returning to field was able to increase organic matter in soil and improve nitrogen use efficiency for the purpose of high yield eventually [2,3]. Compared with the use of stalk, farmyard manure was more favorable to the accumulation of potassium and SOM in limestone soil [4,5]. As research indicated, culture substrate with decomposed cow dung as the main material was able to improve substrate volume weight, total porosity, along with the growth and physiological indicators of pepper seedlings [6,7]. Chemical fertilizer when applied could improve soil fertility to some degree, but it was not so remarkably effective. As some studies indicated, normal farmyard manure when applied was featured with more greenhouse gas emission than chemical fertilizer. However, organic granular fertilizer was effective to increase yield with persistent fertilizer efficiency for soil fertilization, and this was not only favorable to increase after crop production proportionately, but to optimize ecology as well [1,[8][9]. Broadcast application will not give full play to the organic granular fertilizer, and it will only reduce application effects. Then if furrow application or whole application is assumed, better effects may be expected. (2)Stalk returning equipment: mechanical stalk cutting (5-10cm long), returning to field by manual work.

Material and method
(3)Broadcaster for granular chemical fertilizer: single disc broadcaster as developed by Nanjing Agricultural Mechanization Research institute of the National Agriculture Ministry.
(4)The spraying machines and equipment for field fertilizer, pesticide and microbial agent shall be operated conventionally as farmers usually do. decomposed cow dung, 500kg each mu as air-dried basis, moisture 20%, rotary tillage for 20cm on ridges); Zone II (mechanical cutting and crushing for stalk returning and surface application, 400kg per mu, with stalk decomposing agent and chemical nitrogen fertilizer to be used together and sprayed at the same time according to the single factor, then rotary tillage on ridges for 20cm ); Zone Ⅲ

Test Method
(mechanical cutting and crushing for stalk returning first and deep tillage for 30cm further, 400kg per mu, with stalk decomposing agent and chemical nitrogen fertilizer to be used together and sprayed at the same time according to the single factor); Zone IV (mechanical broadcasting of granular fertilizer as biochar-based) and Zone V (conventional management of tillage and fertilizer application, for which 18kg nitrogen, 5kg phosphorus pentoxide, 6kg potassium oxide, urea and potassium chloride 20kg+10kg as the basic fertilizer, 10kg diammonium phosphate as the seed fertilizer, extra fertilization for 225kg/hm at bell stage, or special fertilizer for corns would be selected, and due to stalk returning practice, potash fertilizer amount could be properly reduced ). These experiments started from the year of 2013, and then soil samples were collected in autumn to determine their volume weight, organic matter content and nutrients. Then fertilizer and stalk composition were under analysis.Tasks after crop harvesting or before sowing included stalk returning, broadcasting of organic fertilizer, chemical fertilizer and microbial agent, and soil tillage as well. Soil samples and plant samples were collected according to growth periods (before fertilization and tillage, at elongation stage, at bell stage, at filling stage and at ripe stage).

Effects on available nutrients of arable soil for corns during their different growth periods due to different mechanized soil fertilization methods
At ripe stage, contents of alkali-hydrolyzable nitrogen, available phosphorus and available potassium in topsoil in zone III were all remarkably higher than those with other treatments. This was because stalk returning with deep tillage was able to improve soil structure and accelerate microorganism reproduction and stalk decomposition, then facilitating release of available nutrients. In case of stalk returning and surface application, release of alkali-hydrolyzable nitrogen was quicker, though not so persistent. Available potassium in the decomposed cow dung enjoyed quicker release than the available potassium in the organic granular fertilizer did. Therefore, when compared with surface application, deep tillage helped to improve available nutrients in soil after stalks were crushed and returned to field.  Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Figure 1. Changes of the contents of soil available nutrients in each growth stage of maize

Effects on soil total nutrients, organic matter and C/N for corns at their ripe stage due to different mechanized soil fertilization methods
As compare with situations before fertilization and tillage, total nitrogen and total phosphorus at the arable soil in zone I, zone II, zone III and zone IV increased for 3.19% and 127.71% respectively, while total potassium reduced for 0.91% on the average. Mechanical deep tillage, if combined with crushed stalk returning, was beneficial to improve total nitrogen content at topsoil. Additionally, stalk returning when combined with surface application was able to remarkably improve total phosphorus content at topsoil. Mechanical deep tillage, when compared with surface application, was able to remarkably improve organic matter content in soil. So were organic granular fertilizer when compared with decomposed cow dung, and organic granular fertilizer when compared with conventional fertilizer application. organic matter content in arable soil in zone I, zone II, zone III and zone IV increased for 21.32% on the average, when compared with the situations before fertilization and tillage. Mechanical deep tillage and fertilization did not remarkably influence soil C/N ratio, when compared with conventional fertilization.

Mechanization remarkably was effective on available nutrient increase in soil in the demonstration zone.
Alkalihydrolyzable nitrogen enjoyed its quicker release in case of stalk returning and surface application, though not so persistent. Available potassium in the decomposed cow dung enjoyed quicker release than the available potassium did. Stalk returning with deep tillage, if compared with surface application, was more beneficial to improve available nutrient content in soil.

Mechanization remarkably affected total phosphorus improvement for the arable soil at the demonstration zone.
However, it was less effective on and total nitrogen and total potassium. Crushed stalk returning combined with deep tillage, in addition to decomposed cow dung application, was able to remarkably improve total phosphorus content at topsoil.

.Mechanization did not remarkably influence soil C/N ratio for the arable soil in the demonstration zone.
As compared with conventional fertilization, crushed stalk returning with deep tillage, when organic granular fertilizer broadcasting was also adopted, was able to remarkably improve organic matter content at topsoil. Mechanical deep tillage, when compared with surface application, was more beneficial to improve organic matter content in soil, and so was organic granular fertilizer when compared with decomposed cow dung application.
Based on the analysis above, it is concluded that crushed stalk returning with deep tillage for 30cm is able to remarkably increase the available nutrient content in brown soil at the corn continuous cropping area. Organic granular fertilizer, when compared with decomposed cow dung, is more beneficial to improve organic matter content at topsoil. Thus, for brown soil at the corn continuous cropping area, it is advised that crushed stalk returning combined with deep tillage, in addition to organic granular fertilizer broadcasting by agricultural machinery shall be adopted for management. This practice shall not only remarkably increase soil available nutrient in arable soil, but also improve organic matter content to the effect of loose soil structure and local soil fertility betterment.