Irrigation and nitrogen fertiliser optimisation in protected vegetable fields of northern China:Achieving environmental and agronomic sustainability

Globally,sub-optimal use of nitrogen (N) fertiliser and elevated N irrigation groundwater have led to high leached nitrate (NO_(3)^(–)) losses from protected vegetable field systems.Optimising fertiliser and irrigation management in different soil types is crucial to reduce future N loads from such systems.The present 4-year study examined leached N loads from lysimeter monitoring arrays set up across 18 protected vegetable system sites encompassing the dominant soil types of northern China.The treatments applied at each field site were:1) a high N and high irrigation input treatment (HNHI);2) a low N but high irrigation input treatment (LNHI) and 3) a low N with low irrigation input treatment (LNLI).Results showed that the mean annual leached total nitrogen loads from the HNHI,LNHI and LNLI treatments were 325,294 and 257 kg N ha^(–1) in the fluvo-aquic soil,114,100 and 78 kg N ha^(–1) in the cinnamon soil and 79,68 and 57 kg N ha^(–1) in the black soil,respectively.The N dissolved in irrigation water in the fluvo-aquic soil areas was 8.26-fold higher than in the cinnamon areas.A structural equation model showed that N fertiliser inputs and leaching water amounts explained 14.7 and 81.8%of the variation of leached N loads,respectively.Correspondingly,reducing irrigation water by 21.5%decreased leached N loads by 20.9%,while reducing manure N and chemical N inputs by 22 and 25%decreased leached N loads by only 9.5%. This study highlights that protected vegetable fields dominated by fluvo-aquic soil need management to curtail leached N losses in northern China.

Alum split applications strengthened phosphorus fixation and phosphate sorption in high legacy phosphorus calcareous soil

High phosphorus(P)saturation arising from historic P inputs to protected vegetable fields(PVFs)drives high P mobilisation to waterbodies.Amendment of soils with alum has shown potential in terms of fixing labile P and protecting water quality.The present 15 month pot experiment investigated P stabilisation across single alum application(Alum-1 treatment,20 g alum/kg soil incorporated into soil before the maize was sown),alum split applications(Alum-4 treatment,5 g alum/kg soil incorporated into soil before each crop was sown i.e.4×5 g/kg)and soil only treatment(Control).Results showed that the Alum-1 treatment caused the strongest stabilisation of soil labile P after maize plant removal,whereas the P stabilisation effect was gradually weakened due to the transformation of soil non-labile P to labile P and the reduced active Al^(3+)in soil solution.For the Alum-4 treatment,soil labile P decreased gradually with each crop planting and was lower than the Alum-1 treatment at the end of the final crop removal,without any impairment on plant growth.The better P stabilisation at the end of Alum-4 treatment was closely correlated with a progressive supply of Al^(3+)and a gradual decrease of pH,which resulted in higher contents of poorlycrystalline Al,Fe and exchangeable Ca.These aspects were conducive to increasing the soil P stabilisation and phosphate sorption.In terms of management,growers in continuous cropping systems could utilise split alum applications as a strategy to alleviate P losses in high-P enriched calcareous soil.

Predicting phosphorus sorption isotherm parameters in soil using data of routine laboratory tests

Knowledge of phosphorus(P)sorption dynamics across different soil types could direct agronomic and environmental management of P.The objective of this study was to predict P isotherm parameters for a national soil population using data of routine laboratory tests.Langmuir and Freundlich sorption parameters were calculated from two different ranges(0-25 and 0-50 mg P L^(-1))using an archive of representative agricultural soil types from Ireland.Multiple linear regression(MLR)identified labile forms of aluminium(Al)and iron(Fe),organic matter(OM),cation exchange capacity(CEC),and clay as significant drivers.Langmuir and Freundlich sorption capacities,Freundlich affinity constant,and Langmuir buffer capacity were predicted reliably,with R^(2) of independent validation>0.9.Sorption isotherm parameters were predicted from P sorbed at a single concentration of 50 mg P L^(-1)(S_(50)).An MLR prediction of P sorption maximum in the 0-50 mg P L-1 range was achieved,to an accurate standard,using S_(50),OM,and Mehlich-3 Fe(R^(2) of independent calibration and validation being 0.91 and 0.95,respectively).Using Giles’four shapes of isotherms(C,L,H,and S),L non-strict-and C-shaped isotherm curves accounted for 64% and 27% of the soils,respectively.Hierarchical clustering identified a separation of isotherm curves influenced by two ranges of Mehlich-3 Al.Soils with a low range of Mehlich-3 Al(2.5-698 mg kg^(-1))had no incidence of rapid sorption(C shape).Single point indices,Al,or available soil data make the regression approach a feasible way of predicting Langmuir parameters that could be included with standard agronomic soil P testing.