A field experiment was carried out to evaluate the effects of drip fertigation combined with plant hedgerows on nitrogen and phosphorus runoff losses in intensive pear orchards in the Tai Lake Basin.  Nitrogen and phosphorus runoff over a whole year were measured by using successional runoff water collection devices.  The four experimental treatments were conventional fertilization (CK), drip fertigation (DF), conventional fertilization combined with plant hedgerows (C+H), and drip fertigation combined with plant hedgerows (D+H).  The results from one year of continuous monitoring showed a significant positive correlation between precipitation and surface runoff discharge.  Surface runoff discharge under the treatments without plant hedgerows totaled 15.86% of precipitation, while surface runoff discharge under the treatments with plant hedgerows totaled 12.82% of precipitation.  Plant hedgerows reduced the number of runoff events and the amount of surface runoff.  Precipitation is the main driving force for the loss of nitrogen and phosphorus in surface runoff, and fertilization is an important factor affecting the losses of nitrogen and phosphorus.  In CK, approximately 7.36% of nitrogen and 2.63% of phosphorus from fertilization entered the surface water through runoff.  Drip fertigation reduced the accumulation of nitrogen and phosphorus in the surface soil and lowered the runoff loss concentrations of total nitrogen (TN) and total phosphorus (TP).  Drip fertigation combined with plant hedgerows significantly reduced the overall TN and TP losses by 45.38 and 36.81%, respectively, in comparison to the CK totals.  Drip fertigation increased the vertical migration depth of nitrogen and phosphorus nutrients and reduced the accumulation of nitrogen and phosphorus in the surface soil, which increased the pear yield.  The promotion of drip fertigation combined with plant hedgerows will greatly reduce the losses of nitrogen and phosphorus to runoff and maintain the high fruit yields in the intensive orchards of the Tai Lake Basin.

Nitrogen (N), the major forms of which are nitrate (NO₃^–) and ammonium (NH₄⁺), plays an important role in plant growth and mediation of root development.  However, the role of auxin in root growth in response to different NH₄⁺/NO₃^– ratios remains unclear.  Two tobacco cultivars (Nicotiana tabacum L.) were adopted in this study, which displayed variant growth features under the situations with sole NO₃^– nutrition ratio (NH₄⁺/NO₃^– ratio: 0/100), low NO₃^– nutrition ratio (NH₄⁺/NO₃^– ratio: 97/3), and optimal NH₄⁺/NO₃^– ratio (50/50).  We investigated the effects of the different NH₄⁺/NO₃^– ratios on the formation and elongation of lateral roots (LRs), auxin concentration, DR5::GUS expression, 3H-labeled indole acetic acid ([3H]IAA) transport, and the expression of six PIN genes in tobacco roots.  We also examined the effects of exogenous auxin and a transport inhibitor on LRs growth.  The results are shown as follows, compared to optimal N nutrition conditions, the biomass and nitrogen (N) accumulation were largely reduced by sole and low NO₃^– nutrition treatment in NC89, but no difference was observed in Zhongyan 100.  In most cases, sole and low NO₃^– nutrition impaired the elongation and formation of first-order lateral roots (1° LRs), only in NC89, thus reducing the root growth.  IAA concentration and DR5::GUS expression levels decreased in roots when NC89 was subjected to sole and low NO₃^– nutrition media, suggesting that different NH₄⁺/NO₃^– ratios affect the transport of auxin from leaves to roots.  Results were similar following exogenous NAA application to low NO₃^– nutrition treated seedlings.  Based on direct [3H]IAA transport measurement, the transport of polar auxin from shoots to roots decreased due to low NO₃^– nutrition.  PIN4 expression levels were markedly decreased in roots of NC89 by sole and low NO₃^– nutrition, while they were unaffected in Zhongyan 100 roots.  Overall, our findings suggest that LRs formation in tobacco seedlings is regulated by NH₄⁺/NO₃^– ratios via modifying polar transport of auxin.