IN-SEASON VARIABLE RATE N IN POTATO AND BARLEY PRODUCTION USING OPTICAL SENSING INSTRUMENTATION

Inadequate or excess nitrogen (N) severely impacts yield and potato (Solanum tuberosum L.) tuber quality and malt barley (Hordeum vulgre L.) protein and kernel plumpness. These crops are somewhat unique in their narrow N sufficiency range. Variation across fields with residual soil N and yield potential result in large spatial differences for the optimal N fertilizer rates needed to produce high quality potatoes and malt barley. Recently developed optical sensing technology combined with variable rate spray controller hardware makes it possible to apply N in-season at an unprecedented small scale. The objective of this study is to evaluate the use of optical sensing instrumentation to help manage in-season N for potato and malt barley by correlating the Normalized Difference Vegetation Index (NDVI) with tissue nitrate, yield, and various crop quality parameters. Four potato and five barley locations were used as evaluation sites in eastern Idaho. High correlations of R 2 = 0.83-0.90 were observed in 3 of the 4 potato fields for yield compared to NDVI at two weeks prior to row closure for potato. The correlation between yield and N rate were also very high in these fields with R 2 = 0.88-0.99. Similarly, high correlations of R 2 values of 0.37-0.95 were observed in 4 of the 5 fields when comparing yield with NDVI at Feekes 6 for malt barley. The correlation between yield and N rate were also very high in these fields with R 2 = 0.50-0.99. Other yield and quality parameters were measured and recorded to further evaluate the optical sensor in potatoes and malt barley. Trends and correlations showed useful relationships between NDVI and yield and N Rate.