Effect of Ridge Height, Row Grade, and Field Slope on Nutrient Losses in Runoff in Contour Ridge Systems under Seepage with Rainfall Condition.

Juan An,Huiling Yang,Bin Wang,Jibiao Geng,Hongli Song

doi:10.3390/ijerph18042022

Abstract

Seepage plays a key role in nutrient loss and easily occurs in widely-used contour ridge systems due to the ponding process. However, the characteristics of nutrient loss and its influential factors under seepage with rainfall condition in contour ridge systems are still unclear. In this study, 23 seepage and rainfall simulation experiments are arranged in an orthogonal rotatable central composite design to investigate the role of ridge height, row grade, and field slope on Nitrate (NO3−–N) and Orthophosphate (PO4+3–P) losses resulting from seepage in contour ridge systems. In total, three types of NO3−–N and PO4+3–P loss were observed according to erosion processes of inter-rill–headward, inter-rill–headward–contour failure, and inter-rill–headward–contour failure–rill. Our results demonstrated that second-order polynomial regression models were obtained to predict NO3−–N and PO4+3–P loss with the independent variables of ridge height, row grade, and field slope. Ridge height was the most important factor for nutrient loss, with a significantly positive effect and the greatest contribution (52.35–53.47%). The secondary factor of row grade exerted a significant and negative effect, and was with a contribution of 19.86–24.11% to nutrient loss. The interaction between ridge height and row grade revealed a significantly negative effect on NO3−–N loss, whereas interactions among the three factors did not significantly affect PO4+3–P loss. Field slope only significantly affected NO3−–N loss. The optimal design of a contour ridge system to control nutrient loss was obtained at ridge height of 8 cm, row grade of 2°, and field slope of 6.5°. This study provides a method to assess and model nutrient loss, and improves guidance to implement contour ridge systems in terms of nutrient loss control.

Highlights

Transport of dissolved nutrients from agricultural fields is a significant cause of land degradation and aquatic environmental deterioration around the world, and results in a threat to the capacity of land to provide ecosystem services which are necessary requirement to achieve goals of the sustainable development goals (SDGs) [1,2]
The losses of NO3 − –N and PO4 +3 –P occurred under various seepage discharges ranging from 0.25 to 1.27 L min−1 (Table 2)
For the first type of treatments that experienced inter-rill (I) and headward erosion process (H) (Figure 3b), concentration of NO3 − –N and PO4 +3 –P displayed a gradual decreasing trend during inter-rill erosion process, their loss sharply increased to the maximum before continually decreasing (Figure 4a)

Summary

Introduction

Transport of dissolved nutrients from agricultural fields is a significant cause of land degradation and aquatic environmental deterioration around the world, and results in a threat to the capacity of land to provide ecosystem services which are necessary requirement to achieve goals of the sustainable development goals (SDGs) [1,2]. Nutrient loss in runoff has increasingly become a threat to food security and water quality [3,4]. Nutrient losses of up to 81% for nitrogen and 93% for phosphorus have been discovered in runoff arising from agriculture-related activities in China [5]. Seepage flow plays an important role as conveyers of nitrogen and phosphorus from fields to watercourses. Field and laboratory observations have revealed that NO3 − –N and PO4 +3 –P concentrations and losses in seepage flow were significantly higher than those in surface run-off [7,8,9,10,11]. It is urgent to study the process of nutrient loss

Methods

Results

Discussion

Conclusion