Abstract
BackgroundManagement regime can hugely influence the efficiency of crop production but measuring real-time below-ground responses is difficult. The combination of fertiliser application and mowing or grazing may have a major impact on roots and on the soil nutrient profile and leaching.ResultsA novel approach was developed using low-cost ion-selective sensors to track nitrate (NO3−) movement through soil column profiles sown with the forage crops, Lolium perenne and Medicago sativa. Applications of fertiliser, defoliation of crops and intercropping of the grass and the legume were tested. Sensor measurements were compared with conventional testing of lysimeter and leachate samples. There was little leaching of NO3− through soil profiles with current management practices, as monitored by both methods. After defoliation, the measurements detected a striking increase in soil NO3− in the middle of the column where the greatest density of roots was found. This phenomenon was not detected when no NO3− was applied, and when there was no defoliation, or during intercropping with Medicago.ConclusionMowing or grazing may increase rhizodeposition of carbon that stimulates soil mineralization to release NO3− that is acquired by roots without leaching from the profile. The soil columns and sensors provided a dynamic insight into rhizosphere responses to changes in above-ground management practices.
Highlights
Management regime can hugely influence the efficiency of crop production but measuring real-time below-ground responses is difficult
Soil column NO3− profiles vary with management practices We began by comparing the soil nitrate measurements with the nitrate concentration measurements collected using mini-suction lysimeters (Fig. 2)
In mixed clover and grass swards defoliation caused a change in the composition of microbial populations, there was no significant effect on microbial activity [71], but our data shows there was no commitment release of N O3−. These NO3−-selective sensors can be built in laboratories quickly and cheaply (Additional file 1: Figure S1) and they can measure in real time the available soil water NO3− after calibration with known N O3− concentrations
Summary
Management regime can hugely influence the efficiency of crop production but measuring real-time below-ground responses is difficult. Natural grasslands and forage crops are carbon sinks, important in the context of increasing atmospheric CO2 levels if they are properly managed [3, 4]. Decreasing the high rates of N fertiliser use for animal farming and forage crop production is an important target, especially in high-intensity temporary grasslands. In the UK forage grass and legume crops are predicted to have high leaching rates to the environment with this problem exacerbated when crops are cultivated in sandy soils [9]. N leaching can contaminate human drinking water especially in ground water supplies and may result in decreased life expectancy [12, 13]. N emissions from grassland and animal production contribute to climate change [14, 15]
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