Effects of different mechanized soil fertilization methods on corn nutrient accumulation and yield

Aim: Experiments for mechanized corn soil fertilization were conducted in Faku demonstration zone. On this basis, we studied effects on corn nutrient accumulation and yield traits at brown soil regions due to different mechanized soil fertilization measures. We also evaluated and optimized the regulation effects of mechanized soil fertilization for the purpose of crop yield increase and production efficiency improvement. Method: Based on the survey of soil background value in the demonstration zone, we collected plant samples during different corn growth periods to determine and make statistical analysis. Conclusions: Decomposed cow dung, when under mechanical broadcasting, was able to remarkably increase nitrogen and potassium accumulation content of corns at their ripe stage. Crushed stalk returning combined with deep tillage would remarkably increase phosphorus accumulation content of corn plants. When compared with top application, crushed stalk returning combined with deep tillage would remarkably increase corn thousand kernel weight (TKW). Mechanized broadcasting of granular organic fertilizer and crushed stalk returning combined with deep tillage, when compared with surface application, were able to boost corn yield in the in the demonstration zone.


Introduction
Nowadays, poor mechanization applicability and unreasonable use of organic fertilizer prevail in agricultural production. Extensive cultivation and abuse of chemical fertilizer lead to soil nutrient imbalance and soil fertility decline, so crop nutrient accumulation and yield are impacted [1,2]. Therefore, it is very pressing to study and implement effective measure to improve soil fertility. Alfred Gathorne-Hardy, based on his study from a prospective of sustainable development, found out that mechanization was featured with higher efficiency than cattle ploughing as labor-saving, and both were not so significantly different in terms of greenhouse gas emission [3,4]. Mechanized deep placement could facilitate rice tillering, favorable for rice root system elongation to absorb nutrients, so rice yield increased consequently [5]. Mechanized deep placement as adopted in Japan proved that it was effective for yield increase. It was reported that as for deep placement 35 days prior to rice heading at the agricultural experimental station of Aomori, Japan, nitrogen use efficiency even amounted to 86%. Koyama and others (1973) found that the applicability of nitrogen for whole layer placement was twice as much as that for surface application. Vachhani (1952) stated out that as for granular fertilizer, deep placement around paddy plants was more effective than surface application. Prasad and others (1970) also confirmed that deep placement of nitrogenous fertilizer was better than surface application both in terms of paddy yield and nitrogen uptake [6]. As some studies indicated, when organic granular fertilizer (Aike brand) was combined with urea and potassium sulfate as a practice of mixed application, it was able to increase paddy yield; while there was not so significant difference in paddy yield between organic granular fertilizer of exclusive application (Aike brand) and conventional fertilization [7]. Liu Shujie during his study confirmed that mechanical deep placement of chemical fertilizer was able to increase paddy yield remarkably, and this practice would save fertilizer as well [8]. Research showed that mechanize deep placement of chemical fertilizer was able to increase paddy yield and save fertilizer, too [9, 10]. (2)Corn stalk: local corn stalk (nutrient content: organic carbon 43.54%, N content 0.863%, P content 0.260%, K content 0.834%, moisture 9.07%).
(4)Conventional chemical fertilizer: slow release fertilizer with the brand of Qingyuan, which was used as the base fertilizer for deep placement, 50kg per mu (≈667m2, Chinese traditional unit area and the same below) (NPK content of 27-11-13, zinc 0.02% for the product made by Changjiang Controlled Release Fertilizer Company Ltd., Jilin). Seed fertilizer for surface application: Compound fertilizer of 15-15-15 with the brand of Yanyangtian.
(5)Microbial agent: stalk decomposing agent applied for stalk returning to field.
(2)Stalk returning equipment: mechanical stalk cutting (5-10cm long), returning to field by manual work. (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.

Test Method
On the premise of the same plot with the same soil fertility under the same tillage conditions, five experimental zones were established for our experiments: Zone I (with mechanical broadcasting of 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 (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 ammonium 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). As indicated from table 2, 3 and 4, we could perceive that nitrogen accumulation and potassium accumulation per unit area in treatment I was 17.88% and 84.15%, respectively higher than N and K accumulation per unit area in treatment V. Treatment III, when compared with treatment II, remarkably increased phosphorus and potassium accumulation per unit area at corn ripe stage. Both treatment I and treatment III remarkably increased nitrogen, phosphorus and potassium accumulation per unit area inside plants at corn ripe stage, when compared with conventional cultivation and fertilization. Note: Different letters in the same column mean significant difference at 5% level.

Mechanization effects on yield traits for corns at their ripe stage
Indication from Table 5: bare top length in treatment I was remarkably different from that of the other four treatments. Ear length of treatment I, treatment II, treatment III and treatment V were roughly identical. Ear diameter, cob diameter and ear rows for each treatment were basically identical. Grain number per panicle of treatment V was remarkably larger than that of the other four treatments. Thousand kernel weight (TKW) of treatment I, treatment II, treatment III and treatment IV were remarkably higher than that of treatment V. This means that these four methods of mechanized soil