Average grain yield change of single traits to control (%)
GREEN-MANURE AND NITROGEN-FERTILIZER EFFECTS ON SOIL QUALITY AND PROFITABILITY OF A WHEAT-
K. EL MEJAHED, L. AOURAGH
3.2. Effect of cropping sequence, tillage and nutrient management on yield, nitrogen uptake and water use efficiency of wheat
3.2.1. Yield
Lentil had a pronounced effect on yield of the following wheat crop at NIFA Research Station (Table IX). A similar positive effect on farmers’ fields was not statistically significant. The effects of lentil on yield were more promising at zero tillage and low N-level (30 kg N ha-1) treatments as compared to with-tillage and 60 kg N ha–1. Lentil caused a net increase in grain yield of 0.93 and 0.54 t ha–1 at NIFA and 0.52 and 0.21 t ha–1 on farmers’ fields in zero-tillage and tillage treatments, respectively. Increases in wheat yield (straw + grain) caused by the legume in the sequences (Table X) were equivalent to (on a per-ha basis) Rs.12,280 (US$204) and Rs.13,152 (US$219) at the NIFA Research Station, and Rs.6,020 (US$100) and Rs.2,600 (US$43) on farmers’ fields in zero-tillage and tillage treatments, respectively. These results indicate legume inclusion in the cropping system would provide additional income to farmers under rainfed conditions. Beneficial effects of legume cultivation on subsequent cereal yields has been reported in many studies [22–27]. Besides water, N deficiency is the most important limiting factor for production of wheat and other cereals in Pakistan. For continuous cropping, the N must be supplemented as organic matter and other sources. Next to soil and fertilizer, biological N2 fixation (BNF) is to be considered as an extremely important source of N [28].
Table IX. Effects of cropping sequence, tillage and nutrient treatments on wheat yields at NIFA Research Station and on farmers’ fields, 1999–2000
P1 P2 P3 P4 Sequence
Table X. Net increases in wheat yields from previous lentil and their value Increased
grain yield
Increased straw yield Location Treatment
(kg ha–1)
Valuea of increased yield (grain + straw)
(Rs. ha–1) NIFA Lentil effect, zero tillage
Lentil effect, with tillage
930 539
2,420 4,420
12,280 13,152 Urmar Lentil effect, zero tillage
Lentil effect, with tillage 520
210 930
460 6,020
2,600
a Price of wheat = Rs.400/50 kg for grain and Rs.100/50 kg for straw; Rs 60.00 = US$1.
In Southern and Western Australia, the principal source of N for cereal crops is BNF, either from forage legumes or grain legumes in rotation. The most widespread and consistent effect of legumes is to improve the N economy of soil through BNF. The N balance of a legume-cereal sequence in most cases is more positive than that of a cereal-cereal sequence in the same soil. Thus, the inclusion of legumes in cropping systems can arrest decline of soil-N fertility and reduce requirements for fertilizer N. Similarly, our results indicate that the with-legume sequence enhanced the yield and reduce the fertilizer-N requirement of succeeding wheat at the NIFA Research Station and farmers’ fields under rainfed conditions, possibly due to improvement in soil-N-fertility status and other associated benefits from legumes.
Tillage significantly improved wheat grain yield at NIFA, but did not improve yields on farmers’
fields. This difference may be due to soil texture. The results of Ali [29] support our findings. He observed that deep tillage improved grain yield and WUE of wheat over minimum and zero tillage and the deep tillage impact was significant in a silt-loam but not a sandy soil. The added nutrients significantly improved yields on farmers’ fields and NIFA Research Station; however, the effect was more pronounced on the farmers’ fields. The highest yield was recorded with 60 kg N + 60 kg P ha–1. A residual effect of nutrient applied the previous year was noted only in plots that received 60 kg P ha-1 in combination with N. These plots produced higher yields than those plots previously fertilized with 30 kg P ha–1. The residual effect of nutrients on yield was clearer in wheat–wheat sequences as compared to legume–wheat sequences. In the legume–wheat sequence, 30 kg N along with 30 or 60 kg P ha–1 was found sufficient at the research station to meet N and P requirements of the wheat crop previously fertilized with 60 kg N + 60 kg P ha–1. However, on farmers’ fields, 60 kg N was needed along with 30 or 60 kg P ha–1 for higher yields.
The interaction between nutrient level, tillage and cropping sequence was significant, showing that the highest yield was obtained with tillage treatments and N:P levels of 60:30 and 30:60 in lentil–wheat sequences previously fertilized with 60:60, and lowest in zero tillage and N:P of 30:30 in wheat–wheat sequences. However, on farmers’ fields, highest yields were obtained under zero tillage and N:P levels of 30:60, and 60:30 in lentil–wheat sequences previously fertilized with 60:60.
3.2.2. Intercropping.
Wheat was grown in the alternate rows previously occupied by lentil during the 1998–1999 season.
Intercropped wheat production on a unit-area basis was higher than for sole wheat, although it received 40 kg N ha–1 compared to 60 kg N ha–1 applied to the sole crop (Table XI). Cereals intercropped with grain legumes generally benefit from the association in terms of increased grain and N per unit area compared to monocropped cereals [30]. The N benefit derives from the N-sparing effect of the legume, rather than from concurrent transfer of biologically fixed N to the cereal.
Table XI. Effects of intercropping and tillage on wheat grain yield at NIFA Research Station and on farmers’ fields, 1999–2000
Tillage
T0a T1 Mean Location Cropping system
(kg ha–1)
NIFA Intercropb 2,667 3,267 2,967
Monocrop (wheat followed by lentil) 4,631 5,342 4,986 Monocrop (wheat followed by wheat) 3,700 4,804 4,252
Urmar Intercrop 1,083 1,450 1,267
Monocrop (wheat followed by lentil) 2,044 2,032 2,038 Monocrop (wheat followed by wheat) 1,698 1,828 1,762
Jalozai Intercrop 933 900 916
Monocrop (wheat followed by lentil) 1,749 1,686 1,718 Monocrop (wheat followed by wheat) 1,516 1,490 1,503
a No tillage; T1 = Conventional tillage.
b Intercropped yield was obtained from half of the area as 50% was lentil.
One of the commonly reported advantages of intercropping (legumes with cereals) over monocropping is higher productivity. This is sometimes attributed to transfer of fixed N to the non-N2-fixing crop [31]. Higher nutrient-utilization efficiency has been observed in intercropped than in pure-stand maize [32].
It was reported that when wheat was grown with various legumes (pure or intercropped), pigeon pea preceding wheat did not leave much residual fertility whereas black gram, groundnut and cowpea for fodder gave benefits equivalent to 40 to 80 kg N ha–1 to wheat [33]. However, several studies have failed to demonstrate significant transfer of N from a legume to an associated cereal [34,35]. Thus, contributions from the soil N-sparing effect have been shown in crop-rotation experiments to be more important than N-transfer [24,36].
3.2.3. Nitrogen uptake.
At NIFA, N uptake by wheat straw and grain was significantly influenced by cropping sequence, tillage and nutrient level (Table XII). The interaction between cropping sequence, tillage and nutrient level was significant, showing that the lentil–wheat sequence with tillage led to higher N uptake at all nutrient levels as compared to no-tillage and wheat followed by wheat. Maximum N uptake by grain was recorded in the plots receiving 60 kg N ha–1 in combination with 30 or 60 kg P ha–1.
On farmers’ fields, N uptake by wheat grain was not significantly influenced by tillage, but it was improved by increased nutrient level and by the lentil–wheat as compared to wheat–wheat sequence (Table XII). Higher N-uptake values in wheat straw and grain were recorded under the lentil–wheat sequence at all nutrient levels. Grain- and straw-N yields were least in the continuous wheat sequence both at the research station and on the farmers’ fields and greatest in the lentil–wheat sequence. The amounts of N in grain were greater than in straw, probably due to translocation of N from straw to grain. Similarly, Strong et al. [37] found that uptake of N by wheat was higher in a legume–wheat sequences compared with cereal–wheat sequences.
3.2.4. Utilization of residual nitrogen
Less than 1% of the fertilizer applied the previous year (1998–1999) was utilized at the NIFA Research Station by the subsequent wheat crop (data not shown). Tillage led to greater utilization of N than no-tillage, but higher %Ndff values were recorded in no-tillage treatments at all N and P levels.
Table XII. Effects of cropping sequence, tillage and nutrient treatment on wheat-grain nitrogen yield,
On farmers’ fields at Urmar and Jalozai, the %Ndff, fertilizer-N yield and %N-utilization values for residual 15N-urea were lower than at NIFA Research Station. A greater %N utilization at Urmar was recorded for the lentil–wheat sequence than for wheat–wheat. However, tillage and nutrient level had no clear effect.
3.2.5. Carbon-isotope discrimination
The 13C-discrimination data revealed that, at NIFA Research Station, the values for straw and grain were more negative under tillage than zero-tillage (Table XIII). However, for nutrient level the values were very close in both grain and straw. These data indicate that higher amounts of water were taken up under tillage. This is confirmed by the WUE data and the moisture status of the soil profile as determined at successive growth stages under tillage and zero-tillage; water contents were higher in tilled plots (Fig. 1). The WUE values of grain indicated a good correlation (R2=0.988) with δ13C values, which became more negative as WUE increased.
Any factor that affects either stomatal conductance or photosynthetic capacity, such as photosynthetically active radiation, water deficit, atmospheric humidity, nutrition, salinity and air pollution will influence δ13C [38,39]. On farmers’ fields, the values were less negative under tillage and lentil–wheat crop sequences as compared tillage and wheat–wheat, but the tillage and zero-tillage values were similar. These results support the yield and rain-use-efficiency data obtained from the farmers’ fields.
Table XIII. Effects of tillage and nutrient level on carbon-isotope discrimination in wheat straw and grain at NIFA Research Station and of farmers’ fields, 1999–2000
Carbon discrimination
The WUE was improved by tillage and the lentil–wheat sequence at the NIFA Research Station as compared to no tillage and the wheat–wheat sequence (Table XIV). The WUE values were higher than other reported values, possibly due to higher fertility status, water-holding capacity and potential productivity of the NIFA soil. Ali [29] also reported higher water use efficiency by wheat due to tillage and NPK application in comparison with zero and minimum tillage in Pakistan.
On farmers’ fields, rainwater use efficiency was enhanced by the lentil–wheat sequence (Table XIV).
However, tillage treatment did not exert any effect. The values ranged between 9.60 to 13.4 kg ha–1 mm–1. The lentil–wheat sequence increased the rainwater use efficiency by 2.28 kg ha–1 mm–1 over the wheat–wheat sequence at Urmar and by 1.36 kg ha-1 mm-1 at Jalozai. The no-tillage treatment showed higher rain use efficiency on both farmers’ fields.
Soil-water content data under wheat at different growth stage — as influenced by tillage treatment and cropping sequence — are summarized in Figs. 1 and 2, respectively. Tillage showed higher moisture content in the soil profile (0–90 cm) at all growth stages except during stem elongation (Fig. 1).
Although the moisture content was higher with tillage treatments, it was very close to the zero-tillage treatment at seedling, tiller initiation and the first tillering stage. However at the second tillering, ear and milky stages, the tillage treatment contained 38.0, 7.95, and 19.7 mm more water, respectively, in the profile than did zero tillage. These higher moisture contents at lower depths in the tillage treatment showed that tillage helped to control 2nd stage evaporation by breaking the capillaries as compared to the no-tillage treatment. Cropping sequence did not have a pronounced effect on the soil moisture content as recorded at different growth stages (Fig. 2). However wheat–wheat and intercropping systems showed higher moisture contents at all growth stages than did lentil–wheat, except at the milky stage. This indicates that legumes may contribute little to the maintenance of higher moisture content in the soil profile for a subsequent crop. The positive effects of lentil on subsequent wheat may be due to other associated benefits from the legume.
FIG. 1. Effect of tillage on soil moisture content under wheat at various growth stages at NIFA Research Station, 1999–2000 (T1=conventional tillage, T0=no tillage).
Seedling stage
FIG. 2. Effect of cropping sequence on soil-moisture content under wheat at various growth stages at NIFA, 1999–2000 (C1 = wheat–wheat, C2 = lentil–wheat, C3 = intercropped lentil/wheat).
Seedling stage
Table XIV. Effects of cropping sequence and tillage on wheat-grain water-use efficiency at NIFA and rainwater use efficiency on farmers’ fields, 1999–2000
T0a T1 Mean
aNo tillage; T1 = conventional tillage.
Soil-surface conditions are a major influence on water content of soil. Bouzza [40] found that water storage increased from 50 to 85 mm as a result of surface-applied straw as compared to treatments in which straw was deeply incorporated. The improved moisture conservation was due to better infiltration and reduced evaporation. Wheat grain yield was higher under no-tillage than clean tillage because of better utilization of growing-season precipitation in residue-covered plots. Similarly, in our experiments on farmers’ fields, the lentil residues (leaves, etc) on the soil surface at maturity worked as a mulch with zero tillage and thus helped reduce surface evaporation and improved utilization of growing season rainfall.
4. CONCLUSIONS
Tillage treatment improved the grain yield of wheat at NIFA Research Station but did not improve yields on farmers’ fields. Fertilizer-N utilization by wheat was greater on farmers’ fields (up to 42% of applied N) than at NIFA (33%). In the case of lentil, grain yield was not influenced by tillage or nutrient level, although N2 fixation was stimulated by the higher P level. Lentil obtained 82 to 96% of its N from fixation and chickpea 52 to 64% under farmers’ conditions. The 13C-discrimination data for wheat grain indicated a positive relationship with grain yield. Lentil exerted a significant effect on the yield of subsequent wheat as compared to a wheat–wheat sequence. Wheat utilized less than 1% of the N applied to the previous year’s crop. Water-use efficiency was improved in the lentil–wheat sequence with tillage at NIFA as compared to no-tillage of the wheat–wheat sequence. However, on farmers’
fields, no-tillage showed higher rainwater-use efficiency.
ACKNOWLEDGMENTS
The authors thank the Pakistan Atomic Energy Commission for approving the project and the International Atomic Energy Agency for sponsorship. The 15N, N and 13C-discrimination analyses were performed by the staff of IAEA Laboratory at Seibersdorf, which is gratefully acknowledged.
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