Impact of manure injection on spatial variability in soil nitrate, carbon, and small grain growth

Abstract

Manure injection alters the spatial distribution of manure by concentrating it in a subsurface band which can lead to differential soil nutrient distribution and growth in small grains. This study assessed the effects of fall manure applications on soil NO3‐N, active carbon, and small grain growth compared to broadcasting and a no manure control. Soil samples were taken to represent whole plot soil means for all treatments, while in‐band (IB) and between‐band (BB) soil samples were taken in injected plots to assess nutrient spatial distribution after injection. Small grain forage samples were also taken IB and BB to assess the effects of manure injection on small grain growth. Soil samples were analyzed for NO3‐N, permanganate oxidizable carbon (POXC), and carbon mineralization (C‐min), while small grain DM yield and forage quality parameters were measured from plant samples. Manure injection did not result in any differences between whole plot injection and broadcast soil NO3‐N concentrations. However, injection resulted in initially elevated soil NO3‐N concentrations IB compared to BB. There were no differences in soil POXC or C‐min under manured vs unmanured soils, nor between IB and BB samples. Manure injection did not increase small grain DM yield or forage quality compared to broadcasting, nor were these measurements altered IB and BB. Even though manure injection altered the spatial distribution of soil NO3‐N, it did not affect soil C‐min and POXC or small grain growth under the conditions seen in this study. Therefore, differential small grain growth and quality is likely not a concern under injection.This article is protected by copyright. All rights reserved

Does fall manure injection cause differential growth and forage nutritive value in small grains?

“…Furthermore, no differences in soil NO 3 -N were observed at silage harvest, indicating that elevated soil N levels were not present to drive a change if N did limit maturity. These results are similar to Hilfiker et al (2023a), who found no differences in-band compared to between-band small grain growth stage at silage harvest. No other studies have examined differential maturity in small grains under injection, and the data presented in this study provides the first evidence that fall dairy manure injection does not lead to differential maturity at silage harvest time.…”

“…As N would likely be the primary driver of increases observed in-band versus between-band, the lack of differences in CP provides further evidence that the increased early season concentration of NO 3 -N in the injection band did not cause increased in-band forage nutritive value to be observed by silage harvest. These results are similar to Hilfiker et al (2023a), who found no changes in CP across 2 years and small grain species at silage harvest when comparing in-band to between-band samples. As with CP, the other forage nutritive value parameters were rarely elevated in-band, with ADL showing significant in-band elevation at two sites, and NDF, IVDMD, and sugars showing in-band elevation at one site each (p < 0.05).…”

“…As with CP, the other forage nutritive value parameters were rarely elevated in-band, with ADL showing significant in-band elevation at two sites, and NDF, IVDMD, and sugars showing in-band elevation at one site each (p < 0.05). These results are also similar to Hilfiker et al (2023a), who found no consistent in-band elevation in NDF, ADF, ADL, IVDMD, and sugars across years and small grain species. While no further studies exist examining small grain forage nutritive value in manure injection bands, the present study and Hilfiker et al (2023a) present the first evidence that manure injection does not cause differential forage nutritive value by silage harvest.…”

“…Similar studies examining soil NO 3 -N spatial distribution under spring injection found no differences when comparing in-band to betweenband soil NO 3 -N concentrations at corn harvest (Bierer et al, 2021;Westerschulte et al, 2017). Furthermore, Hilfiker et al (2023a) found no differences in soil NO 3 -N concentrations when comparing in-band to between-band samples at small grain silage harvest time following a fall manure application. This present study, along with the previously discussed studies, indicates manure injection causes an initial in-band spike in soil NO 3 -N that did not persist throughout the growing season under either corn or small grains.…”

“…The lack of differences observed when topdress N was omitted could be due to the long history of manure applications at each site, which potentially enabled the soil to supply enough N to prevent banding differences from being observed, even without a topdress N application. Hilfiker et al (2023a) found an average increase in DM yield in-band compared to between-band of 24% across 2 study years and small grain species at silage harvest with a topdress N application omitted but did not have topdress N plots for comparison. The sites also had no manure history, which could have resulted in the increased difference observed between bands compared to the present study.…”