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Tillage and nitrogen management in a wheat-maize farming system

Ahmad Khan1, Mohammad Tariq Jan1, Amanullah Jan1, Zahir Shah2 and Shamsher Ali2

1Department of Agronomy, Faculty of Crop Production Science, NWFP Agricultural University Peshawar Pakistan, www.aup.org.edu.pk E-Mail ahmad0936@yahoo.com
2 Department of Soil and Environmental Sciences, Faculty of Crop Production Science, NWFP Agricultural University Peshawar Pakistan,

Abstract

Declining soil fertility and low input farming results in low cereal productivity in semi arid areas of Pakistan. Increasing soil water storage using conservation tillage is essential for sustainable cereal production. The effect of tillage and nitrogen (N) sources was evaluated in randomize complete block design with split plot arrangement for wheat-maize farming system from 2005 to 2007 on silt clay loam soil in western Pakistan. Three tillage practices [i.e. minimum tillage, conventional tillage and deep tillage] were allotted to main plots, whereas 12 N treatment to subplots. Nitrogen treatment include control, 60 and 120 kg N/ha as urea, farm yard manure @ 10 and 20 tons/ha solely or mixed with half of urea N, and soybean residue @ 10 tons/ha solely or mixed with half of urea N. Minimum tillage improved soil moisture, and crop yield, but in 2005 no difference in crop yield was observed compared to conventional tillage. Nitrogen supply solely from farm yard manure or enriched with a small amount of urea (30 or 60 kg N/ha) has increased soil moisture in all years, but only increased crop yield in 2006 and 2007 compared to urea N or from N sources such as soybean residue alone and/or enriched with urea N urea. Farm yard manure @ 20 tons/ha in conjugation with 60 kg N ha (urea) was the optimum input for profitable farming compared to all other treatments, and resulted in 117% improvement in wheat yield and 18% in maize yield over control. Our results has shown that profitable responses to minimum tillage and farm yard manure in wheat and maize can be obtained on long term cultivated silt clay loam soil in Pakistan. This integrative benchmark for greater water storage under minimum tillage and farm yard manure has the potential to improve cereal productivity in semi arid areas of Pakistan and is therefore recommended.

Key Words

Farm yard manure, residue, soil moisture, and cereal crop yield.

Introduction

Wheat (Triticum aestivum L.) and maize (Zea mays L) are influenced by management of the previous crop but is highly dependent on current year management (Wiatrak et al., 2006). This current year management is further influenced by factors such as seasonal rainfall, warm temperatures, reduced radiation use efficiency at low nitrogen (N) supply, high weed infestation and are accountable for poor cereal productivity (Sepaskhah et al., 2006). There is a need for management practices in cropping systems that can reduce the impact of these factors on cereal productivity. Soil in western Pakistan is low in organic matter and tends to be so due to continuous cropping. Addition of organic source of N is thought to be good for developing soil organic belt as well as sustaining crop productivity. However, the application of fertiliser should be limited due to scarce resources and environmental concerns (Sepaskhah et al., 2006). Therefore, the present study was hypothesis to determine the effect of tillage and N source on grain yield and soil water storage in wheat and maize cropping system in semi-arid western Pakistan.

Methods

The effect of different sources of organic and inorganic N added to soil under different tillage practices, were assessed in a 2-year (2005–2007) field experiment on spring wheat (cv. Saleem-2000) and maize (cv. Kissan-92), at the Research Farm of NWFP, Agricultural University Peshawar Pakistan, (17, 35 N and 35, 41 W). The soil of the experimental farm is a silt clay loam. The mean annual rainfall is about 360 mm. The soil is deficient in mineral N (less than 0.08 mg/kg soil and P (less than 20 g/kg soil), but has adequate K (greater than 120 g/kg soil) with a pH of 8.2 and organic matter content <1%.

The experiment was conducted in Randomized Complete Block (RCB) design with split plot arrangement having three replications. Twelve treatments of N in the form of N (urea), Farm yard manure (manure) and soybean residue (SR) were arranged in subplots and three tillage practices [minimum tillage (MT), conventional tillage (CT) and deep tillage (DT)] in main plots. The N treatments were 0kg N/ha (N0), 60kg N/ha (N1), 120kg N/ha (N2), 10 tons manure/ha (Manure1), 20 tons manure/ha (Manure2), 30kg N and 10 tons manure/ha ( N1 + Manure1), 60 kg N and 10 tons manure/ha ( N2+ Manure1), 30 kg N and 20 tons manure/ha ( N1 + Manure2), 60 kg N and 20 tons manure/ha ( N2 + Manure2), 10 tons SR/ha, 30 kg N and 10 tons SR/ha ( N1+ SR), 60 kg N and 10 tons SR/ha ( N2 + SR).

Deep tillage practices were carried out by chisel plough which tilled the soil up to 45 cm followed by a common cultivator. Common cultivator was used for CT which tilled the soil for 30cm. In both DT and CT, the soil was ploughed two times horizontally as well as vertically and planking was done to break the clods and level the field. Minimum tillage practice was done by the use of rotivators to bury only the manure/SR up to the depth of 4-6cm. Farmyard manure was obtained from the Dairy farm of Agricultural University Peshawar, was well decomposed having 1.06 % total N, 16.2% organic matter. Soybean was used as residue crop, was partly decomposed having 3.12% total N and 18.7% organic matter (organic carbon). Incorporation of manure and SR in the field was made 45 days before the sowing in all seasons for 4-6cm deep in the soil using common cultivator and irrigated as flood irrigation. Urea (46% N) was applied in a split application, half at sowing and the other half just after first irrigation (after 27 days).

Subplots of 3 x 5m were used for all the three crops, with 10 rows 30 cm apart with 5 metre length, and 3 replications (only 4 rows 75 cm apart for maize). Analysis of variance (ANOVA) and least significance difference (LSD) test at p < 0.05 was used for hypothesis testing using GenStat release 8.1 (GenStat, 2005).

Three randomly samples of soils (10-15cm depth) were taken in each subplot, weighed fresh, than oven dried at 105C to a constant weight and reweighed for determination of soil moisture. Grain yield was recorded in central six rows (for wheat) and four rows (for maize) of each subplot after threshing separately.

Results

Deep tillage results in lower soil moisture that conventional which is lower than minimum tillage (Fig 1). It is the degree of disturbance that results in moisture loss. Minimum tillage increased soil moisture or crop yield (Table 1) particularly in 2006-7 compared to deep or conventional tillage. Minimum till minimises soil moisture loss which results in more water availability to the crop, hence greater yield in the minimum till plots (Table 1). Application of organic N sources resulted in higher soil moisture (Fig 2) perhaps due to addition of more organic matter. Application of manure either singly or in combination with N increased soil moisture storage compared to control, possibly due to increase in soil organic matter which had increased water holding capacity. Wheat grain yield (Table 1) ranged from 2099 kg/ha (Control) to 4456 kg/ha (20 tons manure/ha + 60 kg N/ha), showing about 112% improvement in yield over control during 2005-06 for wheat crop. In following year (2006-07), this increment over the control for wheat crop was about 122% in combined application of 20 tons manure/ha + 60 kg N/ha. Similarly maize grain yield was more in combined application of manure and urea N compared to other. Organic N sources i.e. manure was better than soybean residues and/or sole urea N for soil moisture, but was not different from urea N when crop yield was taken into account. The differences in soil moister and crop yield for organic source of N became more evident over time compared to urea N. Although there was no greater differences in rain fall over time, except during January 2005 and December 2006 in which average monthly rainfall exceeded 60 mm (Khan at al., 2008).

With increase in mineral N supplied as urea from 0 to 120 kg N/ha, wheat grain yield in all the three tillage practices were increased (Fig 3), being greater in conventional tillage than other. Generally, minimum till plots out yielded than conventional or deep tilled at N supplied whether in the form of manure or soybean residue for either sole or reinforced with N compared to control. Increasing the levels of manure a proportional increased in yield for minimum or conventional tillage was observed unlike for the deep tillage.

Figure 1. Soil moisture (%) in response to tillage. The vertical bars are standard errors of means.

Figure 2. Soil moisture in response to fertility treatment (1= control, 2= sole N, 3= manure, 4= soybean residue, 5= manure + N, 6= soybean residue + N). The vertical bars are standard errors of means.

Table 1. Grain yield of wheat and maize as affected by various N sources under a different tillage practices

Urea N in kg/ha, manure (Farm yard manure) in tons/ha and Soybean residue (S-Residue) in tons/ha
Means followed by same letter (s) with in each category are not significantly different using least significance difference (LSD) test P < 0.05.

Fig 3. Grain yield (kg/ha) of wheat as affected by tillage x N sources interaction over years.

Discussion

In the existing climatic conditions reduced tillage increased soil moisture storage possibly due to less disturbance of existing soil pores, more surface stubble so improving infiltration (Gangwar et al., 2006) or soil porosity (Chiroma et al., 2004) and microbial activity and thus have improved crop yield. More water was retained in the soil layers in manure plots, compared to sole N application and/or control, indicates the modification of soil possibly by addition of organic matter, which prevents runoff and increased the time of ponding for infiltration over time. The reduction of evaporation losses due to the presence of manure (Olasantan, 1999) might be the other possible explanation for improved soil moisture in manured plots over control. Improved crops yield in manure reinforced with N plots could be attributed to the carry-over effects of mineral for optimum growth (Lemcoff and Loomis 1994), or might be due to the more favourable moisture regime in the root zone of the manured treatments or more efficient utilization of nutrients released from decomposition of the added manure by the crop (Chiroma et al., 2006).

Conclusion

Addition of manure to the soil either solely or with urea N, improved soil moisture and thereafter crop yield. High cost of manure transportation hinder the application of sole manure at higher rates, thus its conjunction with a small amount of N (urea) would be an alternative way for providing the optimum amount of nutrient for improving crop yield. In addition to improving crop yield, manure incorporation in soil build soil organic matter for improved water moisture particularly in reduced tillage. Concerning pollution of the environment due to soil disturbance by tillage, the minimum tillage seems to be better than other tillage practices both in term of controlling pollution by less soil disturbance and sustaining yield on long term basis.

Acknowledgement

Thanks to Higher Education Commission Pakistan for financial support under Indigenous Ph. D-5000 Scholarship Programme.

References

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