Sustainable Manure Management in Intensified Corn Production Systems for Maintaining Crop Quality and Yield, Managing Soil Phosphorus, and Increasing Soil Health

Dairy farmers often surface apply phosphorus (P)-based liquid manure to corn (Zea mays L.) for silage, supplementing with N fertilizers for optimum corn nitrogen (N), optimizing crop production while decreasing P loss to the environment. However, injecting manure may further conserve losses and reduce synthetic N fertilizer need. An experiment was conducted on a dairy farm in Breese, IL from May 2019 to April 2022 with two main treatments including (i) surface application of manure at P-based rate supplemented with 123 kg ha-1 synthetic N and (ii) manure injection at P-based rate supplemented with 17 kg ha-1 of synthetic N fertilizer. Both treatments delivered 201 kg N ha-1 to meet corn N need. Our results indicated that yield and quality of silage corn and cereal rye were similar in both treatments. This suggests that injection can limit manure ammonium-N fraction losses and decrease the need for supplemental N fertilizer by 106 kg ha-1, which translates into up to $150 ha-1, while not affecting the quality and quantity of yields. Moreover, the effect of manure injection on soil test P (STP) was similar to that of surface application and did not increase STP over a three-year period. Elevated STP in high P-supplying soils can be an environmental concern, but our results show that neither treatment increased STP. Future research should focus on quantifying N loss through denitrification and leaching when manure is injected versus surface applied to provide a more holistic overview of the soil and environmental impact of each system

Reducing the influence of solar illumination angle when using active optical sensor derived NDVIAOS to infer fAPAR for spring wheat (Triticum aestivum L.)

In recent years, the normalized difference vegetation index (NDVI), derived from active optical sensors (AOS) is being increasingly used to estimate the fraction of absorbed photosynthetically active radiation (fAPAR), a key variable in plant productivity modelling. The fAPAR of a plant canopy is dependent on the solar illumination angle. On the other hand AOSs when used to measure NDVIAOS are responding only to their integrated light source. The consequence is the NDVIAOS-fAPAR relationship is sensitive to solar illumination angle. In this work the effect of aligning the AOS view angle with the solar illumination angle on the NDVIAOS – fAPAR relationship is examined for a range of solar elevation angles (θse) of 40°, 55° and 70°, for spring wheat (Triticum aestivum L., bread var. Crusader), at four different growth stages (Zadoks 26, 29, 39 and 47). At each growth stage the fAPAR - NDVIAOS relationship was linear (R2 ≥ 0.80). The regression lines exhibited similar slopes with varying solar illumination angle, but with some variation in intercept. By aligning the AOS sensor view angle to the solar illumination angle there was no significant difference in the NDVIAOS-fAPAR relationship between Zadoks 26 and 29 nor between Zadoks 39 and 47. The presence of senescent leaves at later stages of crop growth was noted to influence the fAPAR – NDVIAOS relationship, which should be considered when applying a unique algorithm for all stages of crop growth