APEC International Conference on Natural Resources and Infrastructure Management for Agriculture

1. APEC International Conference on Natural Resources and Infrastructure Management for Agriculture Nutrient management adaptation for dryland maize yields and water use efficiency to long-term rainfall variability in China Prof. Dr. CaiDianxiong Institute of Agricultural Resources and Regional Planning ,CAAS Beijing,100081,China dxcai@caas.ac.cn August, 2012 in Bangkok

2. 1. Introduction • Northern China has a large region of dryland farming, which accounts for about 55% of the nation’s total cultivated land. Water scarcity and a large variation in inter-annual and intra-annual rainfall are the main constraints to rainfed crop production, causing low and unstable food production. • Erratic rainfall is a cause of soil and water losses on sloping lands during the summer rainy season and seasonal drought in winter and spring. The wind exacerbates soil drought and causes a reduction in both spring maize seedling emergence and winter wheat growth during most years. • The dryland areas of northern China are highly important for providing food and feed to the growing human and animal populations. Maize accounts for 22% of the total area of food crops, and 26% of the total food production in China . • The effects are exaggerated by the current practices of removing crop residues from the field after harvest, to leave the ploughed soil bare during winter, and to plough the soil again in spring after fertiliser application (for spring maize), and thus cause a reduction in spring crop seedling emergence.

3. In the dryland areas of northern China, crop yield responses to fertiliser application are quite low and variable, due to unbalanced fertiliser use and crop residue removal under traditional tillage systems resulting in inefficiencies of both water use and fertiliser use, and low economical return to farmers. • Soil conservation and improved nutrient management practices are gaining interest of Chinese research and policy communities. • Reduced tillage was introduced in the study area in the early 1990s and it showed to be highly effective in decreasing soil drying and wind erosion, especially with integrated conservation tillage and improved nutrient management practices (Wang et al., 2007). • The practice required that fertilisers, crop residues and manure are applied in autumn prior to ploughing, approximately 6 months before maize is seeded. Applying fertilisers long before the crop growing season is only feasible in dry conditions where nutrient losses are minimal.

4. Many of the Challenges for dryland agriculture are Intensification of Limits that We Currently Address Low and highly variable moisture Severe weather events Periodic drought Unreasonable nutrient and water use in some areas Wind and water erosion Increased soil water and nutrient use efficiency help to address these challenges To optimize the combined application of NP fertilisers, maize stover and cattle manure under reduced tillage practicesmay is one way to face of Challenges of Dryland Farming today.

5. 2.1. Site description The ongoing long-term field experiment started in 1992 at the Dryland Farming Experimental Station in Shouyang, Shanxi province (112–113◦E, 37–38◦N) in northern China. The area has a mean altitude of 1100m above sea level. 2. Materials and methods 材料与方法 • Shouyang county (Shanxi province)

6. Table 1. Site description Parameters Values PPT = 560 - 864 mm PET = 1662 to - 1852 mm AMT = 7.4℃ (- 23.5 - 43.7 °C) RH = ± 65%.. Soil = sandy loam cinnamon soil, ( classified as Calcaric-Fluvic Cambisols ) soil pH = 7.9 SOC =15 g kg−1 Soil organic N (SON) = 1.0 g kg−1 P-Olsen = 7.3 mgkg−1 NH4OAc extractable K = 84mgkg−1 Spring corn Variety = Jindan 48

7. 2.2. Experimental design • The experiment was set up according to an incomplete, optimal design (Xu, 1988) with 3 factors (NP fertiliser, maize stover and cattle manure) at five levels and 12 treatments (see Table 2), including a control treatment and two replications. This experimental design allows the use of a minimal set of factors of the variance–covariance matrix and provides a maximal efficiency of the experiment. • An important condition is that within the range of applications chosen, the optimum responses are found. The procedures of this design are explained in Khuri and Cornell (1987).

8. Table 2. Experiment treatments on combined applications of NP fertiliser, maize stover and cattle manure. Note: Fertiliser N:P2O5 = 1:1.

9. 2.3. Methods • Plots (6m×6m) were laid down randomly in replicates. • The N and P fertilisers were urea (46% N) and superphosphate (7% P) in a ratio of N to P of 1:0.44. • Maize stover and cattle manure were obtained from local farms. The weighted mean contents of organic matter, total N, total P (as P) and total K were 75%, 0.63%, 0.039% and 0.72% for maize stover (ratio of N:P:K = 100:6:114) and 36%, 0.96%, 0.17% and 0.74% for cattle manure (ratio of N:P:K = 100:18:77), respectively. • Maize stover (S), cattle manure (M) and • fertilisers (F) were broadcast and incorporated • into the soil after maize harvest in the fall by • ploughing (20cm deep) with conservation tillage. • Grain yield and crop residues were determined • by harvesting the centre 1.8m×2.1m of the plots.

12. Soil moisture determination Soil temperature measuring Soil carbon emission measuring Yield measuring 研究思路与技术路线

13. 2.4. Data processing and statistical analysis Apparent water use or apparent evapotranspiration (ET, in mm) was calculated from the change in soil water contents between the beginning of the growing season at sowing (SWS, in mm) and the end of the growing season at crop harvest (SWH, in mm) plus rainfall received during the growing season (GSR), viz. ET = (SWS − SWH) + GSR (1) Hence, we assumed that there were no losses via deep drainage and runoff during the growing season. Apparent water use efficiency (WUE, in kg ha−1mm−1) was calculated from grain yield (GY) and ET, according to WUE = GY/ET (2) Statistical analyses were done using GLM, REG and RSREG procedures of the SAS Institute Inc. (2004). The data were subjected to an analysis of variance using the GLM procedure. The mean pairwise comparison was based on the Duncan test at the 0.05 probability level (at P≤0.05). In addition, stepwise multivariate regression analyses were carried out. Linear and nonlinear (parabolic) statistical models were fitted to describe the relationships between GY and added N via fertiliser, crop residues and manure applications, and GSR and SWS.

14. Trime-FM3-Tube-probe (TDR) Methodology Water balance equation

15. Tipping-bucket rain gauge Flume + discharge gauge + drums Datalogger Methodology Water balance equation

16. 1 Ks tension infiltrometer MRC sand box/pressure chamber Htensiometers (Hg) Mualem-van Genuchten (1980) Methodology Water balance equation

17. Methodology Water balance equation 1 2 Plane of zero flux method Mualem-van Genuchten (1980)

18. Methodology Water balance equation Equipotential lines 5 sets of tensiometers 5 m apart

19. 3. Results 3.1. Variation in rainfall and soil water Fig. 1. Annual growing season rainfall (GSR), average amounts of soil water in the upper 2m at sowing (SWS), and apparent water use (ET), in Shouyang during the experimental period 1993–2007.

20. 3.2. Mean grain yield and water use efficiency Table 3 Effects of combined applications of NP fertiliser (F), maize stover (S) and manure (M) on grain yield (GY), water use efficiency (WUE) and evapotranspiration (ET) per treatment, averaged over the whole experimental period (1993–2007). Data from 0 to 200cm soil depth. Note: Values with the same letter within a column are not significantly different at 5% level using the Duncan test of SAS.

21. 3.3. Annual variations in grain yields Fig. 2. Effects of combined applications of NP fertiliser (F), maize stover (S) and manure (M) on grain yield (GY), in the period 1993–2007. Results are shown for the treatments 1, 2, 7, 8, 9, 10 and 12 (the control).

22. Table 4. Coefficients of the regression models for grain yield (GY) and water use efficiency (WUE) as function of NP fertiliser (both linear (Fertiliser) and quadratic (Fsq)), maize stover, and manure, soil water at sowing (SWS) and rainfall during the periods April–June (R(A–J)), July (R(J)) and August–October (R(A–O)), for the whole experimental period 1993–2007. Data from 0 to 200cm soil depth. a PE: parameter estimate; SE: standard error; Pr: probability-value (P-value).

23. 3.4. Annual variations in water use efficiency Fig. 3. Relationships between grain yield and apparent water us for all experimental years and treatments. The lowest and highest water use efficiencies are indicated by the arrows.

24. 4. Discussions and conclusions • 4.1. Grain yield response to rainfall and nutrient management • Grain yields were greatly influenced by SWS and GSR, causing differences between years in the order of 200–300% (e.g. between 1994 and 2007). • GY was limited by the availability of nutrients in the soil. Added NP fertiliser, maize stover and cattle manure increased GY, but effects of NP fertiliser, cattle manure and maize stover were different. • Although added NP fertiliser, maize stover and cattle manure as such increased GY, a balanced combination gave the highest mean yield, about 60% increase relative to the control treatment. • fertilisation effects were smaller than rainfall effects. • Effects on GY appeared to increase over time, but could mainly be attributed to the fact that GY of the control treatment declined due to nutrient depletion of the soil. • Grain yields in some years may also have been affected by diseases (mainly head smut). In this respect, our findings are confirmed by Li et al. (2003) and Bai et al. (2006) who also pointed to decreasing GSR, soil nutrient depletion and diseases as major causes for declining yields.

25. 4.2.Water use efficiency response to rainfall and nutrient management Fig. 4. Calculated relationships (1) between water use efficiency (WUE) and added stover, manure and N fertiliser (upper panels), (2) between WUE and added stover and N fertiliser, and soil water at sowing (SWS) (middle panels), and (3) between WUE and added stover and N fertiliser, and rainfall in July (lower panels), using the equations presented in Table 4

26. 4.2. Water use efficiency response to rainfall and nutrient management • Differences in WUE were much larger between years than between treatments (Fig. 4). • The major factors for explaining WUE differences are: the distribution of the rainfall over the growing season and N availability, particularly soil water at sowing (SWS) and rainfall during tasseling (Table 4). • In Fig. 4, the potential increase of WUE through improved nutrient management is shown. WUE is presented as a function of added N fertiliser (N), and stover (S) with resp. cattle manure, SWS and July rainfall. • Clearly, when calculated as an average over all years, WUE is highest at a (modest) N fertiliser input of about 100 kg ha−1 (WUEN100), and (Fig. 4, top) there is an additional positive effect of stover. • Increasing manure inputs from 0 to 6000 kg ha−1, increases WUE/N100 from about 14 to 15 kg ha−1mm−1 without stover, and from about 17 to 18 kg ha−1mm−1 with S = 6000 kg ha−1. A rise of SWS from 300 to 500mm, will increase WUE/N100 from about 13 to 17 kg ha−1mm−1 without stover, and from about 16 to 20 kg ha−1mm−1 with S = 6000 kg ha−1 (Fig. 4, centre). Higher July rainfall (rising from 50 to 200mm; Fig. 4, bottom), has a similar effect.

27. For rainfed areas, nutrient management should respond to such variable conditions, targeted to the need of the growing crop, in a way commonly termed as ‘response farming’ (Stewart, 1991). The concept of ‘response nutrient management’, such as split applications, provides practical guidelines for improving nutrient management under the variable rainfall conditions. Split application of N fertiliser is a well-established management strategy to improve the N use efficiency of cereal crops (e.g. Schroder et al., 2000; Pattey et al., 2001; Angás et al., 2006). • It is recommended to apply about half or two-thirds of the recommended total N dose at sowing and the supplement after emergence of the crop. The supplemental N should depend on rainfall conditions and the N status of the soil or crop (Schroder et al., 2000), and in dry years, supplemental N should not be applied (Angás et al., 2006). • When applied under the conditions of Shouyang, the first N dressing (up to 100 kg ha−1, depending on stover and manure applications) should be applied after harvest (before ploughing), as in the current experiment. A possible second N dressing (up to 50 kg ha−1) may be applied at the 4–6 leaves stage, depending on early season rainfall and the N status of the soil (Schroder et al., 2000; Dobermann and Cassman, 2002). The feasibility of such split application technology in practice needs to be tested further.

28. 4.3. Conclusions • The results of this long-term field experiment in Shouyang of Shanxin in northern China show that balanced combinations of stover (3000–6000 kg), manure (1500–6000 kg) and NP fertilizer (105 kg) gave the highest maize yield and hence WUE. It is suggested that 100 kgN per ha should be a best choice, to be adapted according to availability of stover and manure. • Nutrient management under the rainfed conditions requires rainfall to be taken into account in a dynamic approach to explain the strong interactions between GSR and the effects of NP fertiliser, stover and manure. • The huge annual variations in grain yields and WUE indicate that there is scope for improvement of water use efficiency by split applications. The concept of ‘response nutrient management’, being an integral part of the ‘response farming’ is applicable to the variable rainfall conditions of the drought-prone area for contributions to high crop yields. • For further improving water use efficiencies, the partitioning of basal and supplemental N dressings need further examination for the variable rainfall conditions of dry land areas in northern China.