Effects Of Fertilization, Mulch And Tillage On Crop Yields And Soil Quality In The Semi-arid Loess Plateau Of China

Recently,a method using double ridges and furrows mulched with plastic film for micro-catchment water harvesting has been rapidly developing for maize owing to its significant effect on increased yields in dry-land farming system.Terraces have a significant effect of rainwater harvesting and soil conservation,so more and more terraces were used in the cultivation of maize with this technique.Terracing of sloping fields has been widely adopted by farmers in semiarid areas.This technique needs significant inputs of money and labor every year,and result in decrease of soil fertility and soil dryness in the deep soil profile.In 2003,one experiment was established to explore the optimum method for improving crop yields and soil fertility in newly built terraces;in 2006,another experiment was established to minimize investment, improve economic benefits and overcome the problems of soil dryness in the deep soil profile and decrease of soil fertility.(1) August 2003 onwards:1) MNP,or sheep manure plus nitrogen and phosphorus,2) NP,or nitrogen and phosphorus but no manure,3) M,or manure alone,that is neither nitrogen nor phosphorus,and 4) CK,or control(check),that is neither fertilizers nor manure.The rotation of field pea(Pisum sativum L.),spring wheat(Triticum aestivum L.),and potato(Solanum tuberosum L.) was applied in newly built terraces.(2) In March 2003,three treatments were established under double ridges and furrows mulched with plastic film:1) plastic-film mulching at maize sowing with conventional tillage,and the film was removed at harvest(CK);2) mulching applied 30 d before sowing with conventional tillage,and the film was removed at harvest(T1);and 3) mulching at sowing with no tillage,and the film left on the field after harvest in the first season and used for mulching in the second season(T2).MNP improved soil water conversation,with the average soil water content in 0-100 cm soil depth over the 6 years increased 26.9mm before sowing date,compared to NP,the value between M and CK was 12.8 mm;Manure treatments(MNP and M) were propitious to increase the soil water content in the 0-40 cm soil layer.Compared to CK,fertilization decreased the soil water content in the 100-200 cm soil layer throughout the duration of the experiment.Total rainfall storage in soil throughout the duration of the growing season for NP,CK,M and MNP were 207.7,217.9,269.7 and 291.8 mm in the 0-200 cm soil layer,respectively.Yields and water use efficiency (WUE) were the highest in MNP,and yields in MNP—as much as 70%of the corresponding yields in established terraces in the region in the case of field pea and spring wheat and 90%in the case of potato.Soil organic carbon(SOC) and soil total nitrogen(TN) built up faster in MNP and M than in CK or NP in the short term.C/N and C/P in MNP have been optimized,but the C/N in NP gradually left equilibrium point.From the third year,mineral nitrogen(MN) and available phosphorus(AP) were significantly higher in MNP than in other treatments.A significantly positive correlation was found between AP and MN(R=0.869;P＜0.0001) and N/P(MN/TP) (R=0.860,P＜0.0001).A significantly positive correlation was found between MN and crop yields.So MN was very important for improving crop yields in newly built terraces.The results suggest farmers should be encouraged to apply manure and chemical fertilizers to achieve higher yields,conserve moisture,and accelerate the build-up of fertility in newly built terraces on the Loess Plateau of China.The T1 in both years and T2 in the second year(2007) improved soil water content(in the 0-60 cm layer) and temperature(10 cm) at sowing compared with CK. After the two seasons,the soil water content was significantly higher in the 0-80 cm soil layer in CK and T1,and in the 0-120 cm soil layer in T2;however,it decreased significantly in 140-200 cm soil layer in CK and T1,compared to their initial values at sowing in April 2006,and there was no significant change in T2.The rainfall storage in the 0-200 cm soil layer during the non-growing season(late September 2006 to late April 2007) was 18.2 mm in CK,34.0 mm in T1,and 59.7 mm in T2,and the rainfall storage in 100-200 cm soil layer was 16.5 and 18.6 mm higher in T2 than in CK and T1,respectively.In 2006,there were no significant differences in yield and water use efficiency(WUE) in all treatments.In 2007,the yield in T1 was significantly higher than in T2,but yields in T2 and CK were not significantly different,and there was no significant difference in WUE among treatments.The ratio of output to input was 1.32:1 for CK,1.40:1 for T1,and 1.67:1 for T2 averaged across the two seasons.SOC and TN(0-20 cm) decreased in CK and T1,but slightly increased in T2 at harvesting in September 2007 from the initial value of sowing in April 2006。AP was significantly higher in T2 and T1 than in CK at sowing in April 2007,while AP was significantly higher in T2 than in T1and CK at harvesting in September 2007.AP,soil micro-biomass carbon(MBC) and nitrogen(MBN) were significantly increased,but MN and light fraction of organic carbon(LFOC) significantly decreased in all treatments at harvesting in September 2007 from the initial value of sowing in March 2006.Significant negative correlation is found between MBC and LFOC,and MBC and MN,but positive correlation is found between MBC and AP.Therefore,adoption of double ridge-furrows of mulching with plastic films coupled with no tillage was a more sustainable model for increasing water storage,producing greater economic benefit,maintaining balance of SOC and TN balance,and improving AP for maize production in semiarid area.In conclusion,MNP is the optimum treatment for conserving soil water, enhancing crop yields and WUE of newly built terraces;T2 was a more sustainable model for increasing water storage,producing greater economic benefit,maintaining balance of SOC and TN balance,and improving AP for maize production in the semi-arid Loess Plateau of China.