Research Article

Integration of Biochar and Legumes in Summer Gap for Enhancing Productivity of Cereal Based Cropping System

Muhammad Arif1, Fazal Jalal1, Mohammad Tariq Jan1, Dost Muhammad2

1Department of Agronomy; 2Department of Soil and Environmental Sciences, The University of Agriculture, Peshawar, Pakistan.

Editor | Tahir Sarwar, The University of Agriculture, Peshawar, Pakistan

*Correspondence | Fazal Jalal, The University of Agriculture Peshawar, Pakistan; E-mail | jalal_146@yahoo.com

Citation | Arif, M., Jalal, F., Jan, M., T., Muhammad, D. 2014. Integration of biochar and legumes in summer gap for enhancing productivity of cereal based cropping system. Sarhad Journal of Agriculture, 30(4): 393-403.

Keywords | Maize, biochar, legumes and nitrogen levels

Introduction

In Pakistan cereal based cropping systems are predominantly followed due to higher farm income and ensuring food security. These crops require high amount of nutrient due to their exhaustive nature (Timsina et al., 2006). For obtaining higher yield of crops, fertilization with primary nutrients like N, P and K is considered vital. However, the crop productivity decreases with the passage of time and currently higher doses of nutrients are required for achieving high yields of the crops (Gill et al., 2008). This situation is further aggravated with worsening fertility of the soils and causes several nutrient deficiencies including those of micronutrients. For sustainable crop production, the practice of organic matter buildup is important as organic matter is life of soil and improves soil structure and texture (Behera et al., 2007). Crop residue incorporation is a useful practice for improving microbial activity and stabilizing organic matter content of soil (Palm et al., 2001). Legumes which have unique quality to fix atmospheric nitrogen increase soil fertility are almost eliminated from cropping system due to low economic yield and other socioeconomic constraints (Ojiem et al., 2007).

Biochar is a fine grained charcoal high in organic carbon and largely resistant to decomposition. It is produced from pyrolysis of plants and other organic waste feed stocks. Biochar application has received a growing interest as a sustainable technology to improve highly weathered or degraded soils (Lehmann and Rondon, 2006). It can enhance plant growth by improving soil chemical characteristics, physical characteristics and biological properties all contributing to an increased crop productivity (Yamato et al., 2006). Crop yield are usually increased when biochar are applied along with chemical fertilizers (Steiner et al., 2007). Crop yield and soil fertility are increased with application of nitrogen fertilizers (Ogola et al., 2002). Nitrogen fertilizer in combination with crop residue has positive effects on plant growth and production as well as on soil fertility (Khan et al., 2009). Increase in soil total nitrogen was observed due to beneficial effect of N with organic fertilizers (residue or FYM) (Malhi et al., 2006).

Currently the use of living materials as nourishments for crop production has received attention for sustainable crop yield (Tejada et al., 2009). Agrarian are involved to establish an agricultural system, which can reduce cost of production and conserve the natural resources. Therefore, interest in organic manuring has re-emerged due to significance of green manure and high fertilizer prices. Long-term soil productivity can be achieved through the application of organic manures that maintain along with meeting timely requirement of nutrients. Urea and organic material show a pleasant effect for plant as source of nitrogen (Bocchi and Tano, 1994).

There are few studies quantifying the relative contribution of biochar and legumes in summer gap towards N economy, productivity, profitability and soil fertility in cereal based cropping system. Hence, a comprehensive study was undertaken to study the direct and residual effects of biochar and legumes on enhancing productivity, improving soil quality and getting sustainability in cereal based cropping system.

Material and Methods

The current study was conducted at NDF, the University of Agriculture Peshawar during 2011-2013. Wheat-maize-wheat cropping pattern was followed for the experiments. The summer legumes were adjusted in the summer gap (land available after wheat harvest till maize sowing from last week of April to mid July) for grain, fodder and green manure purposes. Mungbean (cv. NIAB-2006) was used for grain purpose and cowpea (cv. Ebony) was used for fodder purpose. Likewise, sesbania (Sebania aculeate, cv. Peshawari) was purely used for green manure purpose. A fallow was included in the experiment as control. Biochar was also applied at the rate of 0 and 50 t ha-1. Four N levels to the subsequent maize crop were also included in the experiment. Summer legumes (mungbean, cowpea and sesbania with and without biochar) were grown on 03 May after the harvest of uniformly grown wheat crop. The seeds of mungbean, cowpea and sesbania were treated with proper inoculums to ensure maximum nodulation. The biomass of sesbania was incorporated into the field with a disc harrow in first weak of July.

After land preparation, each plot of the previous legumes’ experiment was split into four sub plots to accommodate four levels of N to maize crop. Maize was sown with four levels of N fertilizer (0, 90, 120 and 150 kg ha-1) on 15-July. Nitrogen was applied to maize through urea in two equal splits, half each at sowing and 30 days of growth. Similarly, the recommended rate of phosphorus fertilizer was applied at the rate of 90 kg ha-1 to maize at sowing. A plot size of 5 m x 16 m was used for legumes’ experiment. For maize’s experiment, the plot of the previous legume’s experiment was split into four sub plots to accommodate four levels of N. In this way, the subplot size became 5 m by 4 m. The biomass of sesbania was weighed before incorporation. The same experiments were repeated on the same plots without disturbing the demarcation of each sub plot for two years (2011-2012 and 2012-2013).

Treatments for legumes’ experiment were as follow:

T1= Mungbean (grain purpose) + 0 t ha-1 Biochar, T2= Mungbean (grain purpose) + 50 t ha-1 Biochar, T3= Cowpea (fodder purpose) + 0 t ha-1, T4= Cowpea (fodder purpose) + 50 t ha-1, T5= Sesbania (green manure) + 0 t ha-1 Biochar, T6= Sesbania (green manure) + 50 t ha-1 Biochar, T7 = Fallow + 0 t ha-1 Biochar, T8 = Fallow + 50 t ha-1 Biochar

The biochar used in these experiments was produced using a traditional ‘on-farm’ method common for small-scale production of charcoal in Pakistan. Acacia (Acacia spp.) wood was pyrolysed at 300-500 oC for 24 h, and pulverized to form a coarse powder. The pH (6.84 ±0.02) and EC (3040 ±101 μS cm-1) were determined in 1:1 w/v biochar-to-distilled water samples with standard electrodes. Similarly, it had 40% C, 2.25% N, 0.14% P, 2052 mg kg-1 K, 450 mg kg-1 Na, 2.24% Ca, and 0.92% Mg. 

Treatments for maize experiment were as follow:

Nitrogen levels for maize

0 , 90, 120, 150 kg ha-1

Data were recorded on the following parameters of maize crop:

Plant height (cm), grains ear-1, thousand grain weight (g), grain yield (kg ha-1), biological yield (kg ha-1) and harvest index (%).

Statistical analysis

The data were analyzed according to ANOVA technique appropriate for Randomized Complete Block (RCB) design with split plot arrangement for maize experiment using Statistix 8.1 software. The treatment means were compared at P<0.05 level of probability using LSD test (Jan et al., 2009).

Meteorological data

The mean monthly temperature and rainfall data from May 2011 to April 2013 during the growing season of both years at experimental site are shown in figure 1.

Results and Discusion

Plant height (cm)

Data concerning plant height of maize are reported in table 1. Statistical analysis of the data indicated that year as a source of variation did not significantly affect plant height of maize. However, biochar and legumes significantly affected plant height of maize. Similarly, plant height was also significantly affected by nitrogen levels. All interactions were not significant for plant height of maize. The application of biochar increased plant height of maize. Biochar application at the rate of 50 t ha-1 produced taller plants as compared to no biochar application. Likewise, plots previously sown with legumes produced taller plants as compared to plots previously kept fallow. In similar way, plant height increased with increasing level of nitrogen. Taller plants were recorded in plots treated with 150 or 120 kg N ha-1 followed by N level of 90 kg ha-1. These results are in agreement with the findings of Verheijen et al. (2004) who reported that biochar application to soils enhances plant growth. Our results agree with Lopez et al. (2007) reported that increase in nitrogen application improved plant height of maize. These results are also in line with Chan et al. (2007) who reported that combined use of biochar and fertilizers enhanced plant height.

 

Figure 1. Mean monthly temperature and rainfall data from May 2011 to April 2013.

 

Table 1. Effect of biochar, legumes and nitrogen levels on plant height (cm) of maize.

					Nitrogen (kg ha-1)
Biochar (BC) ton ha-1	Legumes (L)			0		90			120	150		BC x L
0	Cowpea			193		203			214	205		204
0	Mungbean			188		196			208	197		197
0	Sesbania			173		194			207	209		196
0	Fallow			174		186			191	195		187
50	Cowpea			203		201			210	217		208
50	Mungbean			189		207			211	220		207
50	Sesbania			197		209			212	219		209
50	Fallow			174		195			204	206		195
						BC x N						Mean
0				182		195			205	201		196 b
50				191		203			209	215		205 a
						L x N						Mean
	Cowpea			198		202			212	211		206 a
	Mungbean			189		201			210	208		202 a
	Sesbania			185		201			209	214		202 a
	Fallow			174		191			197	200		191 b
				187 c		199 b			207 a	208 a
	Year			2011-2012					2012-2013
				199					202
Main effects				LSD(0.05)				Interactions			Significance level
Year				Ns				BC x L			ns
Biochar (BC)				*				BC x N			ns
Legumes(L)				5.53				L x N			ns
Nitrogen (N)				4.92				BC x L x N			ns

Means the same category followed by different letters are significantly different from each other at 5% level of probability.

* = Significant at 5% level of probability, ns = Non significant

Number of grains ear-1

Data regarding number of grains ear-1 of maize are presented in table 2. Biochar application did not significantly affect number of grains ear-1 however; legumes and nitrogen levels significantly affected number of grains ear-1. Year as source of variation also had significant effect on number of grains ear-1. The interactions between BC x N and L x N for number of grains ear-1 were significant. All other interactions were non-significant. Legumes enhanced number of grains ear-1 in maize crop. The plots previously sown with sesbania gave more numbers of grains ear-1 as compared to cowpea, mungbean and fallow. Maximum number of grains ear-1 was produced when the crop was given nitrogen fertilizer at the rate of 120 kg N ha-1 followed by 150 kg N ha-1 whereas minimum number of grain ear-1 was recorded in control plots. The interaction between BCxL showed that previously fallow plots without biochar gave minimum number of grains ear-1 however; the incorporation of sesbania with and without biochar gave maximum number of grains ear-1. In case of LxN interaction, higher number of grains ear-1 was counted in plots fertilized with 120 kg N ha-1 where formerly sesbania was incorporated as compared to minimum number of grains ear-1 in fallow plots without N application. Plots previously sown with sesbania improved grains ear-1 in comparison with other legumes and fallow. Legumes produced heavier grains of maize as compared to fallow treatment. Similar results are reported

Table 2. Effect of biochar, legumes and nitrogen levels on grains ear-1 of maize.

					Nitrogen (kg ha-1)
Biochar (BC) ton ha-1		Legumes (L)		0		90	120	150	BCxL
0		Cowpea		436		444	469	421	443
0		Mungbean		431		433	461	477	450
0		Sesbania		453		475	548	502	494
0		Fallow		426		435	464	433	440
50		Cowpea		415		453	474	426	442
50		Mungbean		434		448	479	544	476
50		Sesbania		460		466	548	507	495
50		Fallow		408		450	501	534	473
						BC x N			Mean
0				436		447	486	458	457
50				429		454	500	503	472
						L x N			Mean
		Cowpea		426		449	471	424	442 b
		Mungbean		433		441	470	511	463 b
		Sesbania		456		471	548	504	495 a
		Fallow		417		442	482	483	456 b
				433 c		451 c	493 a	481 b
		Year		2011-2012		2012-2013
				445 b		484 a
Main effects				LSD(0.05)			Interactions	Significance level
Year				*			BC x L	ns
Biochar (BC)				ns			BC x N	*
Legumes(L)				26.93			L x N	*
Nitrogen (N)				19.56			BC x L x N	ns

Means the same categories followed by different letters are significantly different from each other at 5% level of probability.

* = Significant at 5% level of probability, ns = Non significant

by Humphreys (1994) who found that forage legumes improved soil fertility, yield and its related parameters. In similar manner, Ahmad (2000) reported that nitrogen application enhanced yield and yield components in wheat. Abiye and Saleem (1995) reported that nitrogen fixing legumes may suggest an attractive sound means of reducing inputs and increasing profitable outputs of the crop. Ali et al. (1999) reported that total N fixed by legumes increased the dry matter and yield related attribute of maize. Hayat et al. (2008) reported that legumes in rotation with cereals gave higher dry matter and yield production in maize.

Thousand grain weight (g)

Data on thousand grain weight of maize are given in table 3. Analysis of data revealed that legumes and nitrogen significantly affected thousand grains weight however, the effect of biochar was not significant. Year as source of variation also significantly affected thousand grains weight. All interactions were not significant for thousand grains weight of maize. Legumes cultivation as a preceding crop had pleasant effects on thousand grains weight of maize. Plots previously sown with mungbean, cowpea or sesbania produced heavier grains as compared to fallow plots. Likewise, nitrogen application improved thousand grains weight as compared to control plots. Higher thousand grains weight was recorded in plots where the cropwas given nitrogen fertilizer at the rate of 120 kg ha-1 followed by 150 and 90 kg ha-1 as compared to minimum thousand grains weight in control plots. The increased thousand grains weight in fertilized plots may be due the accessibility of nitrogen at grain filling stage which may have resulted in higher thousand

Table 3. Effect of biochar, legumes and nitrogen levels on thousand grain weight (g) of maize.

					Nitrogen (kg ha-1)
Biochar (BC) ton ha-1		Legumes (L)		0		90	120	150	BC x L
0		Cowpea		233		240	257	230	240
0		Mungbean		239		240	262	230	243
0		Sesbania		213		231	244	233	230
0		Fallow		195		215	246	234	222
50		Cowpea		226		235	262	259	245
50		Mungbean		247		236	254	251	247
50		Sesbania		235		243	261	237	244
50		Fallow		202		227	234	232	224
						BCxN			Mean
0				220		231	252	232	234
50				227		235	253	245	240
						LxN			Mean
		Cowpea		229		237	259	244	242 a
		Mungbean		243		238	258	240	245 a
		Sesbania		224		237	252	235	237 a
		Fallow		198		221	240	233	223 b
				224 c		233 b	252 a	238 b
		Year		2011-2012		2012-2013
				214 b		260 a
Main effects				LSD(0.05)			Interactions	Significance level
Year				*			BC x L	ns
Biochar (BC)				ns			BC x N	ns
Legumes (L)				12.02			L x N	ns
Nitrogen(N)				9.51			ns	ns

Means the same categories followed by different letters are significantly different from each other at 5% level of probability.

* = Significant at 5% level of probability, ns = Non significant

grains weight. Ahmad (2000) reported that thousand grains weight and grain yield in maize increased with increase in nitrogen application. These results are also in line with Chan et al. (2007) who reported that the combination of biochar and nitrogen increased plant yield.

Grain yield (kg ha-1)

Data concerning grain yield of maize are reported in table 4. Statistical analysis of the data showed that legumes, biochar and nitrogen levels significantly affected grain yield of maize. Year as source of variation also had significant effect on grain yield of maize. All interactions were found non-significant except BCxL. Legumes as preceding crop improved grain yield of maize. The plots previously sown with cowpea, mungbean or sesbania produced higher grain yield as compared to fallow which resulted in minimum grain yield. Biochar application also enhanced grain yield and its application at the rate of 50 t ha-1 produced higher grain yield as compared to no biochar treatment. Likewise, nitrogen application constantly increased grain yield from 0 to 120 kg ha-1 but thereafter was no significant increase in grain yield of maize. Maximum grain yield was recorded in plots treated with fertilizer N at the rate of 120 kg ha-1 as compared to minimum grain yield in control plots. The interaction between BCxL showed that maize plots having previously cowpea plus biochar gave higher grain yield as compared to minimum grain yield in

Table 4. Effect of biochar, legumes and nitrogen levels on grain yield (kg ha-1) of maize.

		Nitrogen (kg ha-1)
Biochar (BC) ton ha-1	Legumes(L)	0	90	120	150	BC xL
0	Cowpea	1904	2439	3135	3032	2628
0	Mungbean	2123	2511	3038	3173	2711
0	Sesbania	2054	2258	3041	2839	2548
0	Fallow	2000	2249	3147	3194	2647
50	Cowpea	2658	2397	3833	3663	3138
50	Mungbean	2710	2669	3159	3065	2901
50	Sesbania	2495	2708	3397	3073	2918
50	Fallow	1977	2400	2639	2650	2416
			BC x N			Mean
0		2021	2364	3090	3060	2634 b
50		2460	2544	3257	3113	2843 a
			L x N			Mean
	Cowpea	2281	2418	3484	3348	2883 a
	Mungbean	2417	2590	3099	3119	2806 a
	Sesbania	2275	2483	3219	2956	2733 a
	Fallow	1988	2324	2893	2922	2532 b
		2240 c	2454 b	3174 a	3086 a
	Year	2011-2012	2012-2013
		2375 b	3102 a
Main effects		LSD(0.05)		Interactions	Significance level
Year		*		BC x L	*
Biochar (BC)		*		L x N	ns
Legumes (L)		191.17		BC x N	ns
Nitrogen (N)		160.64		BC x L x N	ns

Means of the same category followed by different letters are significantly different from each other at 5% level of probability.

* = Significant at 5% level of probability, ns = Non significant

previously fallow plots with biochar. Aslam and Mehmood (2003) reported that improved organic matter and physical characteristics of soil increase soil fertility and can play an important role in the growth and yield of cereal crops. Verheijen et al. (2004) reported that biochar application improves soil functions such as soil physical and biological properties resulting in higher grain yield. Asai et al. (2009) reported that application of biochar resulted in higher grain yields. The increase in grain yield may be due to sufficient nitrogen availability in soil. These results are in agreement with Ogola et al. (2002) who observed an increase of 43-68% in grain yield due to nitrogen application. Shafi et al. (2007) reported that nitrogen application significantly enhances the crop production in the course of additional nitrogen. This may be due to previously sufficient nutrients available in soil resulting maximum biological yield. The adequate availability of nitrogen in soil made the crop prolific resulting in maximum biological yield. Steiner et al. (2008) reported that the N recovery in biomass was significantly higher when the soil contained additional fertilizers. Danga et al. (2009) reported that grain legumes grown in turning round with annual cereal crops contribute to the total pool of nitrogen in the soil and improve the yield of cereals.

Biological yield (kg ha-1)

Data on biological yield of maize are presented in table 5. Year as a source of variation significantly affected biological yield of maize. The application of biochar did not significantly increase biological yield. Legumes and nitrogen levels significantly affected biological yield. The BCxL and LxN interactions were significant, while rest of interactions were not significant. Legumes as preceding crop improved biological yield of maize. The plots previously sown with cowpea, sesbania or mungbean produced higher bi-

Table 5. Effect of biochar, legumes and nitrogen levels on biological yield (kg ha-1) of maize.

					Nitrogen (kg ha-1)
Biochar (BC) ton ha-1		Legumes (L)		0		90	120	150	BC x L
0		Cowpea		5193		6134	7378	8127	6708
0		Mungbean		5080		6153	7766	7295	6574
0		Sesbania		5512		6399	8060	7767	6935
0		Fallow		4742		5457	6642	7294	6034
50		Cowpea		6453		7305	9344	10480	8396
50		Mungbean		5953		6610	8878	8644	7521
50		Sesbania		6204		6828	8192	8206	7358
50		Fallow		5045		5994	6470	6814	6081
						BCxN			Mean
0				5193		6134	7378	8127	6708 a
50				5080		6153	7766	7295	6574 b
						L x N			Mean
		Cowpea		5823		6720	8361	9303	7552 a
		Mungbean		5516		6382	8322	7969	7047 a
		Sesbania		5858		6614	8126	7987	7146 a
		Fallow		4893		5725	6556	7054	6057 b
				5523 c		6360 b	7841 a	8078 a
		Year		2011-2012		2012-2013
				6278 b		7623 a
Main effects				LSD(0.05)			Interactions	Significance level
Year				*			BC x L	*
Biochar(BC)				*			L x N	*
Legumes(L)				600.17			BC x N	ns
Nitrogen (N)				351.25			BC x L x N	ns

Means of the same category followed by different letters are significantly different from each other at 5% level of probability.

* = Significant at 5% level of probability, ns = Non significant.

ological yield as compared to previously fallow plots. Likewise, biological yield consistently improved with increasing nitrogen levels till 120 kg ha-1 but there was no significant increase with further increase in nitrogen level. Higher biological yield was recorded in plots when the crop was given nitrogen fertilizer at the rate of 150 kg ha-1 as compared to minimum biological yield in control plots. The in teraction between BCxL showed that plots having previously cowpea plus biochar gave maximum biological yield as compared to minimum biological yield in fallow plots without biochar application. In case of LxN interaction, maximum biological yield was noted in plots fertilized with 150 kg N ha-1 where cowpea was previously sown in comparison with minimum biological yield in fallow plots without N application. Plots previously sown with legumes enhanced biological yields of maize as compared to fallow treatment. Aslam and Mehmood (2003) reported that improved organic matter and physical characteristics of soil increase soil fertility and can play an important role in the growth and yield of maize crops. Akbar et al. (2002) reported that growth parameters including biological yield increased with increasing nitrogen rates.

Harvest Index (%)

Data regarding harvest index are presented in table 6. Year as source of variation did not significantly affect harvest index. Likewise, legumes and biochar did not significantly affect harvest index of maize. Similarly,

Table 6. Effect of biochar, legumes and nitrogen levels on harvest index (%) of maize.

			Nitrogen (kg ha-1)
Biochar (BC) ton ha-1	Legumes (L)	0	90	120	150	BC x L
0	Cowpea	34	37	44	38	38
0	Mungbean	40	41	40	43	41
0	Sesbania	34	36	38	36	36
0	Fallow	39	41	47	44	43
50	Cowpea	39	33	41	37	38
50	Mungbean	43	40	36	36	39
50	Sesbania	40	40	42	39	40
50	Fallow	37	40	40	39	39
			BC x N			Mean
0		37	39	42	40	40
50		40	38	40	38	39
			L x N			Mean
	Cowpea	37	35	43	38	38
	Mungbean	42	41	38	39	40
	Sesbania	37	38	40	37	38
	Fallow	38	41	44	41	41
		38	39	41	39
	Year	2011-2012	2012-2013
		38	41
Main effects		LSD(0.05)		Interactions	Significance level
Year		ns		BC x L	*
Biochar(BC)		ns		L x N	*
Legumes(L)		ns		BC x N	*
Nitrogen (N)		ns		BC x L x N	ns

* = Significant at 5% level of probability, ns = Non significant

nitrogen levels also did not significantly affect harvest index of maize. All interactions except BCxLxN significantly affected harvest index of maize crop. Legumes x biochar interaction showed that maize plots having previously mungbean gave maximum harvest index without biochar inclusion. Legumes x nitrogen interaction showed that maximum harvest index was noted in fallow plots fertilized with 120 kg N ha-1. The BCxN interaction indicated that maximum harvest index was recorded in plots fertilized with 120 kg

N ha-1 without biochar incorporation. Maximum harvest index of maize by legumes was probably due to release of macro in addition to micro nutrients from the organic source favorably affected growth yield and yield components which ultimately increased grain yield and harvest index. These results are in line with Rao and Shaktawat (2002) who reported that residual effect of combinations of profitable nitrogenous and organic fertilizer resulted in maximum harvest indexes. The LxN interaction indicated that maximum harvest index was noted in fallow crop fertilized with 120 kg N ha-1 without biochar application. This might be due to high nitrogen levels which positively interacted with light as well as environmental factors to enhance photosynthesis, producing more harvest index. Soni and Sikarwar (1991) observed the residual effect of applied varying fertilizer levels on subsequent wheat crops showing positive effect on yield of wheat.

Conclusion and Discussion

Legumes had pleasant effects on subsequent crop maize in term of improving grain yield and soil properties (N and organic matter). Biochar application significantly increased grain yield of maize. Higher grain and biological yields of maize were obtained with 120 kg N ha-1 in place of its recommended dose of 150 kg N ha-1 when sown after legumes. Similarly, plots previously sown with either cowpea or mungbean resulted in higher grain yield of maize.

References

• Abiye, A. and M. Saleem. 1995. Soil Water dynamics under cereal and forage legume mixtures on drained Vertisols in Ethiopian highlands. Agric. Water Manag. 27:17-24.Ahmad, R., S.M. Shahzad, A. Khalid, M. Arshad and M.H. Mahmood. 2007. Growth and yield response of wheat (Triticum aestivum L.) and maize (Zea mayzs L.) to nitrogen and L-Tryptophan enriched compost. Pak. J. Bot., 39(2): 541-549.
• Akbar, H., M. Ullah, M.T. Jan, A. Jan and Ihsanullah. 2002. Yield potential of sweet corn as influenced by different levels of nitrogen and plant population. Asian J. Plant Sci. 1(6): 631-633.
• Ali, S., W.B. Naseem and A. Ali. 1999. Establishment of productive and sustainable legume-cereal rotations in Pothwar, Pakistan. Pak. J. Soil Sci. (17): 23-28.
• Asai, H., B.K. Samson, H.M. Stephan, K. Songyikhangsuthor, K. Hommaa, Y. Kiyono, Y. Inoue, T. Shiraiwa and T. Horie. 2009. Biochar amendment techniques for upland rice production in Northern Laos. Field Crops Res. 111: 81–84.
• Aslam, M. and G. Mehmood. 2003. Economic feasibility of crop rotations under different rainfall zones. J. Agric. 35:27-23.
• Behera, U.K., A.R. Sharma and H.N. Pandey. 2007. Sustaining productivity of wheat-soybean cropping system through integrated nutrient management practices on the Vertisols of central India. Plant sci. 297: 185-199.
• Bocchi, S. and F. Tano.1994. Effect of cattle manure and component of pig slurry on maize growth and production. Europ. J. Agron. 3: 235-41.
• Chan, K.Y., L. V.I. Zwieten, A. Downie and S. Joseph. 2007. Agronomic values of green waste biochar as a soil amendment. Aust. J. Soil Res. 45: 629- 634.
• Danga, B.O., J.P. Ouma, I.I.C. Wakindiki and A. Bartal. 2009. Legume–wheat rotation effects on residual soil moisture, nitrogen and wheat yield in tropical regions. Adv. Agron. 101: 315–349.
• Gill, M.S., S.S. Pal and I.P.S. Ahlawat. 2008. Approaches for sustainability of rice (Oryza sativa) - wheat (Triticum aestivum) cropping system in Indo-Gangetic plains of India. A review: Indian J. Agron. 53(2): 8196.
• Hayat, R., A. safdar, T.S. Muhammad and H.T. Chatha. 2008. Biological nitrogen fixation of summer legumes and their residual effects on subsequent rainfed wheat yield. Pak. J. Bot. 40(2): 711-722.
• Humphreys, G.W., C. Romani, A. Olson, M.J. Riddoch and J. Duncan. 1994. Non-spatial extinction following lesions of the parietal lobe in humans. Nature. 372: 357–359.
• Jan, M.T., P. Shah, P.A. Hollington, M.J. Khan and Q. Sohail. 2009. Agriculture Research: Design and Analysis, A Monograph. NWFP Agricultural University Peshawar, Pakistan.
• Khan, A., M.T. Jan, K.B. Marwat and M. Arif. 2009. Organic and inorganic nitrogen treatment effect on plant and yield attributes of maize in a different tillage system. Pak. J. Bot. 41:99-108.
• Lehmann, J., J. Gauntand and M. Rondon. 2006. Biochar sequestration in terrestrial ecosystems. A review. Mitigation and Adaptation Strategies for Global Change. 11(2): 403-427.
• López-Bellido, L., R.J. López-Bellido and R. Redondo. 2007. Nitrogen efficiency in wheat under rainfed Mediterranean conditions as affected by split nitrogen application. Field Crops Res. 94: 86–97.
• Malhi, S.S., R. Lemke, Z.H. Wang and B.S. Chhabra. 2006. Tillage, nitrogen and crop residue effects on crop yield, nutrient uptake, soil quality, and greenhouse gas emissions. Soil and Tillage Res. 90: 171-183.
• Ogola, J.B.O., T.R. Wheerler and P.M. Haris. 2002. Effect of nitrogen and irrigation on water use of maize crops. Field crop Res.78 : 105-117.
• Ojiem, J.O., B. Vanlauwe, N.D. Ridder and K.E. Giller 2007. Niche based assessment of contributions of legumes to the nitrogen economy of Western Kenya smallholder farms. Plant. Soil. 292:119–135.
• Palm, C.A., K.E. Giller, P.L. Mafongoya, M.J. Swift 2001. Management of organic matter in the tropics: translating theory into practice. Nutr. Cycl. Agroecosystm. 61: 63-75.
• Shafi, M., J. Bakht, M.T. Jan and Z. Shah. 2007. Soil C and N dynamics and maize yield as affected by cropping system and residue management in North Western Pakistan. Soil and Tillage Res. 94: 520-529.
• Steiner, C., B. Glaser, W.G. Teixeira, J. L. Winfried, E.H. Blumand W.Zech 2008. Nitrogen retention and plant uptake on a highly weathered central Amazonian Ferralsol amended with compost and charcoal. J. Plant Nutr. Soil Sci.171: 893–899.
• Tejeda, M., M.T. Hernandez and C. Garcia. 2009. Soil restoration using composted plant residues: Effect on soil properties. Soil and till. Res. 102: 109-117.
• Timsina, J., M.A. Quayyum, D.J. Connor, M. Saleque, F. Haq, G.M. Panaullah, M. Jahan and R.A. Begum. 2006. Effect of fertilizer and mungbean residue management on total productivity, soil fertility and N-use efficiency in intensified rice–wheat systems. Int. J. Agric. Res. 1(1): 41-52.
• Verheijen, F., S. Jeffery, A.C. Bastos, M.V.D. Velde and I. Diafas. 2004. A critical scientific review of effects on soil properties, processes and functions. Luxembourg: Office for Official Publications of the Eur Com.
• Yamato, M., Y. Okimori, I.F. Wibowo, S. Anshiori and M. Ogawa. 2006. Effects of the application of charred bark of Acacia mangium on the yield of maize, cowpea and peanut, and soil chemical properties in South Sumatra, Indonesia. Soil Sci and Plant Nutri. 52: 489–495.