Variable Rate Technology and Cotton Yield Response in Texas

Variable Rate Technology （VRT） takes within-field variability into consideration and aims to match resource application to crop requirement. Even though Texas is the most important cotton producing state in the US, the rate of VRT adoption is very low here. Hence, analyzing the factors influencing the adoption and providing a regional estimate of the impact of VRT adoption on cotton yield is very important. This study used the 2009 Southern Cotton Precision Farming Survey to analyze the farm and farmer characteristics affecting the adoption of VRT among Texas cotton farmers and to empirically estimate the impact of adoption of VRT on cotton yield in Texas. A two-stage least square procedure with a logistic regression model in the first stage and a multiple linear regression model in the second stage was used to analyze the data. The study revealed that there are significant regional differences in adoption pattern within the state of Texas; and the farmers from the coastal region, where there is higher within-field variability, were more likely to adopt VRT compared to other regions. Younger farmers, farmers managing larger farms, and farmers who use computers for farming operations were more likely to adopt VRT. The results also showed that, on an average, the adoption of VRT does not lead to significant yield improvements for cotton in Texas. Since the impact of VRT adoption on yield is not significant, the source of economic advantage of VRT adoption in Texas may be the reduction of input cost.

Evaluation of Variable Rate Technology for Fertilizer Application in Permanent Pastures

This paper describes the field tests carried out to evaluate the new Vicon RS-EDW centrifugal fertilizer spreader, to be used in Precision Agriculture. The results of initial dynamic calibration tests showed a significant and systematic difference between the application rates of the two discs （about 20%）. This difference had to be corrected by the manufacturer that carried out the necessary changes to the electric actuators. The fertilizer spreader had good distribution homogeneity, considering different working velocities and different positions in the parcel. The pattern distribution curve for 18% super phosphate fertilizer led to an effective working width of 28 meters, with a coefficient of variation of 15%. The longitudinal test, under experimental working conditions led to a machine delay time of 6-7 seconds. The results show an actual fertilization application density between 74%-90% of that determined for each location. These results confirm that the spreader can be used to spread fertilizer differentially in the field.

Development of a variable rate applicator for uniform fertilizer spreading

Environmental impact and economic concerns have driven a variable rate technology(VRT).Spinner spreaders were mainly used for granular fertilizer application since they are simple in design,inexpensive,and can cover large areas.However,the spreader was not adequate for VRT because uniformity changes drastically while varying application rates.Thus,the purpose of this study was to develop a variable rate applicator with uniform spreading patterns.A commercial spreader was modified with a controller and electric actuators for controlling fertilizer discharge directions and amounts.Database was established to determine the optimum discharge direction according to the fertilizer application amount.The uniformity of spreading patterns in accordance with the spread amount per set unit area was evaluated by the statistical coefficient of variation(CV)lower than 15%is assumed to prevent damage to the crop.Test results showed that CVs were 8%,9%,and 8%,respectively,for a tractor in race track mode(adjacent passes in same direction of travel)at 200 kg/hm^(2),300 kg/hm^(2),and 400 kg/hm^(2).This indicates that the fertilizer was spread uniformly,while the coefficient of variation was 12%at 200 kg/hm^(2) in back and forth mode(adjacent passes in the opposite direction of travel).Overall,the results suggest that the race track mode is suitable for operation of a tractor to ensure uniform spreading of fertilizer when applying at variable rates.The future goal is to establish a system for automatic variable rate application according to location in connection with soil analysis and geographic information systems.

Design and experiment of vertical pneumatic fertilization system with spiral Geneva mechanism

In the traditional fertilization method,a large amount of fertilizer is applied,which causes congestion easily.It is not conducive to the sustainable development of agriculture.In this work,a vertical pneumatic fertilization system with a spiral Geneva mechanism was designed according to the operational requirements of variable-rate and smooth fertilization.The uniformity in discharging fertilizer with different spiral angles was simulated and analyzed by extended discrete element method(EDEM)based simulation software,from where the spiral angle of the fertilizer discharge wheel was determined to be 45°.The fertilization system includes a fertilizer apparatus with a spiral Geneva mechanism,whose optimal performance parameters were obtained from the bench experiment.The accuracy and uniformity of the fertilizer application system were taken as the evaluation indicators.The linear relationships of the discharged amount of fertilizer with the rotational speed and the opening of the fertilizer discharging wheel were verified by both static blowing fertilization and field experiments.The static blowing experimental results show that the discharged amount of fertilizer has a high linear correlation and accuracy with both the opening and rotational speed,and the highest correlation occurs with the rotational speed.The rotational speed and opening have significant effects on the discharged amount of fertilizer and the average coefficient of variation.The effect of the rotational speed was the most significant.According to the model obtained by multiple regression fittings,the optimal parameters were determined when the average coefficient of variation was small,the rotational speed was 15.9 r/min and the opening was 34.4 mm.Therefore,the purpose of precise fertilization can be achieved by adjusting the opening or rotational speed in a way to get the exact amount of fertilizer discharged as required by the corresponding crops.The field experiment showed that the variation coefficient of each fertilizer discharged decreases first and then increases with an increasing opening under different rotational speeds,which is consistent with the theoretical value.When the opening was 40 mm or 50 mm,the variation coefficient reached the minimum value,which is far less than the qualified index of 7.8%.In the static blowing experiment and the dynamic field experiment,the stability of the fertilizer discharging device can be significantly enhanced with the utilization of the pneumatic conveying fertilizer.This study can provide a theoretical reference for parameter selection and optimization of vertical spiral fertilization systems.