Landscape Management of Agronomic Processes for Site-specific Farming
The objective of this project is to measure and model landscape dynamics for a hummocky topography in the Black Soil Zone of east central Alberta. Then evaluate the potential benefit of variable rate application.
IPNI-1999-CAN-AB19
23 May 2001
2000
Summary
This is the second year of this project at the field site located in the Black soil zone of eastcentral Alberta. The field site is characterized by rolling topography. Installation of the soil moisture and temperature sensors connected to dataloggers at one landscape transect (shoulder, backslope and footslope positions) was completed. Measurement of soil nutrient dynamics using plant root simulator ion exchange probes, crop growth and crop nutrient uptake dynamics was also completed. Results indicate that landscape position has a significant impact on water redistribution and soil temperature regimes. The shoulder and backslope is drier with very little subsoil infiltration compared to the footslope position. The shoulder is also warmer with greater temperature fluctuations than the backslope and footslope positions. The differences in the moisture and temperature regimes among the landscape positions influences crop growth, soil nutrient dynamics and crop uptake of nutrients. Evaluation of the ecosys model indicates a good prediction of soil moisture and temperature dynamics. Future work will evaluate the nutrient dynamics and crop growth functions of ecosys. In addition, other models (EPIC and DSSAT) will be evaluated using the data from this site.
Detailed Results
Crop yields ranged across the variable topography of the field. In 1997 wheat yields ranged from 15 to 100 bu/A, barley in 1998 ranged from 15 to 100 bu/A, in 1999 canola yields ranged from 15 to 60 bu/A, and in 2000 wheat yields ranged from 10 to 120 bu/A. In all years the highest yields were from the lower slope positions, and the lowest yields from the upper slope positions.
Landscape position was also found to have a significant impact on water redistribution and soil temperature measured. The shoulder and backslope was drier with very little subsoil infiltration, compared to the footslope position. The shoulder slope was also warmer with greater temperature fluctuations than the backslope and footslope positions.
The in-situ PRS probe results showed that nutrient levels increased initially until mid summer and then decreased by late summer. Phosphorus and potassium dynamics appear to be similar, with the drier shoulder position being either the lowest, or only equal to the backslope and footslope positions. The drier environment of the shoulder reduced solubility of P and subsequent crop availability. Potassium levels in the soil decreased in moving from the high organic matter and moist footslope up to the dry shoulder slope. It is speculated that this higher K level in the footslope regions also reflects the higher historic crop residue production in this area.
The role of soil temperature and moisture in controlling the crop response was documented in this study. As temperature and moisture conditions increase, nutrient availability increases. As the crop develops, plant demand for nutrients increase and soil nutrient availability declines. As the crop demand for nutrients declines near maturity, soil nutrient availability increases due to such process as mineralization.
As with nutrient release, crop growth reflected water supply. Leaf area index and crop biomass yield was always highest in the footslope and lowest on the shoulder, as were crop nutrient uptake levels. Crop type was found to differ, in that cereals have higher N uptake than canola, while canola has higher P, K and S uptake.
The results of this study of detailed soil, nutrient, water and crop growth processes at the landscape level are expected to aid in the development of management strategies for precision agriculture. While the highest yield potential is in the footslope positions, this is the field position where you are most likely to encounter flooding or lodging. Alternatively, the shoulder slope areas are typically those with the lowest yield, reflecting the harsh environmental conditions as a result of higher soil temperature, more evaporation, poor water infiltration into the subsoil and greater water runoff. Compared to the shoulder, the backslope has much lower soil temperatures, higher organic matter levels and better subsoil moisture dynamics. It is the backslope landscape position that may present the greatest opportunity to manage fertilizer application to increase crop productivity on rolling landscapes.