Submitted to: European Conference on Precision Agriculture Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/10/1997
Publication Date: N/A
Interpretive Summary: Growing conditions vary across commercial fields resulting in some areas with very good yield and quality and some areas with poor yield and quality. Even though growing conditions vary, water and fertilizer are usually applied evenly across the fields. Applying too much water or fertilizer wastes money and can cause problems such as rot. Too little can nresult in stunted growth. New equipment is now available that can apply different amounts of water and fertilizer depending on what each part of the field needs. "Prescriptions" are needed which specify the optimal level of water and fertilizer for various growing conditions. A team of research scientists studied two very hilly, commercial potato fields to understand how variability in growing conditions contributed to potato yield and quality. When entire fields were evaluated, there was no relationship between the levels of phosphorus and potassium (required plant tnutrients) in the soil and yield, but if only the lower yielding sections were taken into account, there was a slight relationship between yield and phosphorus and a strong relationship between yield and potassium. This indicates that when there is enough fertilizer present, other factors are more important in determining if yield will be good or poor, but if there isn't enough fertilizer, yield will be reduced. Yield was better near the tops of the hills than it was down in the valleys. The low areas had more rotten potatoes, possibly caused by too much water settling in them. The valleys were also cooler resulting in more damage from a late spring frost. Understanding how the variations in growing conditions affect yield is necessary for the development of crop management prescriptions that result in good yield and quality without wasting unnecessary water and fertilizer.
Technical Abstract: Precision crop management requires knowledge of the spatial variability of growing conditions within and between fields and an understanding of the impact of variability on crop yield and quality. Team research in commercial, irrigated fields growing "Shepody" potatoes included mapping of pre-plant soil P and K values, topography, weeds, yield, and tuber quality including specific gravity, tuber weight, and internal and external defects. Point measurements were converted to raster format for easier analysis with GIS software. In areas of insufficient coverage, a non- parametric distance weighting algorithm was used to estimate cell values. Yield was not correlated with soil P and K when the entire data set was used. When only the low yielding areas were included in the analysis, there was a weak correlation between yield and P and a strong correlation between yield and K. Yield was positively correlated with elevation and negatively correlated with slope. Drainage and microclimate factors were influenced by slope and elevation. Specific gravity was negatively correlated with tuber size. High specific gravity and large tuber size are both desirable characteristics. The negative correlation suggests some tradeoffs in management strategies might be necessary. There was a weak positive correlation between weed density and yield due to the extra soil carried over the yield monitor in areas with more weeds, rather than higher yields. Technologies to site-specifically apply inputs on potatoes and to spatially quantify yield and quality are now available. Site-specific prescriptions that determine the optimal levels for inputs are still needed. Producers must identify yield and quality goals, then apply appropriate site-specific management strategies.