Sustainable Cropping System Intensification in Arid Region of India: Fallow Replacement with Limited Duration Sorghum–Legume Intercropping Followed by Eruca sativa Mill. Grown on Conserved Soil Moisture

Abstract

A field experiment was conducted to explore the possibilities of sustainable crop intensification in the fallow–Eruca sativa Mill. system in arid ecology by replacing fallow with short-duration sorghum–legume intercropping. The experiment was laid out in a split-plot design with two planting systems (bed and conventional) in main plots and a factorial combination of crop duration (50 and 60 days) and cropping systems (sole sorghum, sorghum + cowpea, sorghum + Sesbania in 2:2 ratio) in sub-plots. In the succeeding Eruca sativa crop, residuals and two gypsum levels (0 and 250 kg ha⁻¹) were tested. Bed planting practiced during both seasons did not improve the system productivity to significant levels. Extending the duration of fallow replacement crops from 50 to 60 days significantly increased their forage yield, overall system productivity by 25–34%, and system net returns by 15.9–21.5%. Amongst the intercropping systems, the sorghum + Sesbania system added 10–13 tonnes ha⁻¹ Sesbania biomass to the soil, resulting in higher soil organic carbon, available nitrogen, dehydrogenase activity, and residual soil moisture, which increased the yield of the succeeding Eruca sativa crop by 8.8–15% compared to the residual of sole sorghum. However, it could not compensate for the yield loss due to the utilization of 50% of the area for growing the green manure crop. The sorghum + cowpea intercropping–Eruca sativa system was found to be the optimum combination with a system productivity of 1.27–1.87 Mg ha⁻¹Eruca sativa seed equivalent. The productivity of Eruca sativa further improved by 9.5–23.7% due to the soil application of gypsum @ 250 kg ha⁻¹. When averaged over treatments, fallow replacement during the rainy season reduced the available soil moisture at the sowing of Eruca sativa by 8.3–22.8% and subsequently its yield by 16.5–30.4% compared to the fallow–Eruca sativa system. However, with this production penalty, an additional rainy-season fodder crop was successfully grown, which improved the system productivity by 57.7–82.8%, net returns by 31.2–57.3%, and rainfall use efficiency from 0.21 to 36 USD/mm⁻¹ ha⁻¹. Hence, it may be concluded that short-duration fodder crops may be taken as fallow replacement crops for higher system productivity and rainfall use efficiency.

1. Introduction

Meeting the diverse needs of agricultural products for the additional 2 billion people expected over the next 30 years is the biggest challenge for humanity. This cannot be addressed alone by putting new land under cultivation. According to estimates, agriculture currently occupies 13.3% of the global land, with a potential expansion to 16.3% [1]. It is clear that this increased demand will have to be met from existing farmland. Reducing “yield gaps” and/or raising the crop intensity appear to be the potential options, but these are often constrained by the low availability of water and nutrients. This is especially relevant for arid regions, which account for 17.2% of the global drylands [1]. Farming in arid regions is primarily rainfed, and drought is a typical occurrence, resulting in low and unstable agricultural yields. Fallowing is commonly practiced here to reduce uncertainties in production. During fallowing, a proportion of rainfall is conserved in the soil profile, which is then available for the crops grown in the ensuing season [2]. Additionally, it encourages the release of nitrogen (N) via the N mineralization of soil organic matter [3]. However, fallowing leaves land without any crops during the rainy season, creating a lost production opportunity. Fallowing is now considered a less efficient technique. For instance, the precipitation storage efficiency under fallowing is 40% in the semi-arid tropics of South Asia and 10–37% in the Great Plains of North America [4,5]. It has been observed that only a small portion of the rainfall received is stored during fallowing, with the remainder being lost through soil evaporation and deep percolation, which are considerably higher in arid regions [6].

It has always been a researchable issue whether to improve the efficiency of fallowing by improving management practices or to replace the fallowing for varying duration [7,8,9]. It also remains to be seen whether the two main attractive features of fallowing (i.e., conserving rainwater and providing soil N benefits) can be retained using alternative strategies. The options tried were fallow replacement with cover crops or green manures [10,11], forage crops [12,13,14,15], short-season grain crops [16,17], or forage cereal–legume mixture [12,13,14,15]. The success of these approaches depended primarily on precipitation and other climatic factors. For instance, cover crops have been successfully grown in the higher-rainfall-receiving Northern Great Plains of the USA but not in the lesser-rainfall-receiving Central and Southern Plains [17,18]. In some studies, the short-term benefits of nitrogen fixation from a green manure crop or grain production from short-season crops were often not enough to compensate for the reduction in soil water and yield of subsequent crops [10,11,19,20,21]. In India, fallow replacement was found to be technically and economically feasible in vertisols of semi-arid tropics under rainfed situations [22] and in light soils of arid regions under irrigated situations [23]. To achieve sustainable intensification through fallow replacement in arid regions, management practices such as selection of fallow replacement crops, duration, moisture conservation practices, planting method, nutrient application, etc., must be standardized. Bed planting, for example, offers an exciting opportunity to save soil moisture and nutrients. Furrows can function as in situ water collection structures, while beds improve soil physical conditions and nutrient status [24].

With this background, it was proposed to develop a rainfed cropping system whereby initial rains were used to grow fodder crops for a limited duration rather than full-season fallowing. The subsequent showers were then allowed to replenish profile soil moisture to be used for growing drought-hardy oilseed crop Eruca sativa Mill. (commonly known as Rocket or arugula). It has a very efficient root system that can extract moisture and nutrients from deeper layers [25]. It is a preferred crop in the drylands of South Asia under situations when stored soil moisture is insufficient for more profitable crops such as mustard and chickpea. The seeds contain approximately 45% erucic acid and about 9% gadoleic acid [26]. Its oil is used as a lubricant or biodiesel [27]. Because Eruca sativa crop residue is non-edible, and arid farming relies heavily on livestock, it was envisaged that adding fodder crops for fallow replacement would result in a more sustainable farming system. Sorghum is the common rainy-season fodder crop grown in the fringes of the arid region of South Asia. Since it is a moisture- and nutrient-exhaustive crop, the opportunity cost of lost production from succeeding post-rainy-season crops could be substantial. Hence, it was thought to replace fifty percent of it by intercropping legumes (as green manure or fodder) that can improve the attributes of soil water conservation and soil N benefits. Sesbania aculeata Pers. is the most common green manure crop often grown as a sole or intercropped in additive or replacement series. It not only improved soil organic matter and the growth of succeeding crops but also positively influenced the production of companion fodder crops in the current season [23,28,29]. However, it remained to be seen whether the increase in soil fertility causing yield improvements in the production of companion crops and succeeding crops could make up for the fifty percent penalty in area utilized for its cultivation. Alternatively, a leguminous forage crop such as cowpea intercropped with sorghum may have a similar or somewhat lower beneficial effect as Sesbania green manure in enhancing fertility or utilizing less moisture, but can also be harvested as a cash crop that needs to be evaluated [30,31]. Mixed fodder of cowpea and sorghum would be of higher quality and could have a positive residual effect on succeeding crops [32,33]. The productivity of a cropping system can further be improved through better nutrient management of the succeeding post-rainy-season Eruca sativa crop. Oilseed crops require considerable amounts of sulfur; it has been calculated that 16 kg of sulfur is required to produce 1 Mg of seeds [34,35]. Ahmad et al. (1998) [36] also observed a significant interaction between sulfur and nitrogen for seed and oil production in oilseed crops. Gypsum, being the least expensive source of sulfur, suits a minimal input requiring oilseed crop such as Eruca sativa. To verify these hypotheses, an experiment was carried out with the following objectives: (i) to determine the effect of rainy-season cropping, its duration, and planting system on available soil moisture for succeeding Eruca sativa crop and its productivity; (ii) to assess the system productivity, profitability, and rainfall use efficiency of fallow replacement–Eruca sativa systems.

2. Materials and Methods

2.1. Experimental Site

A field experiment was conducted at the ICAR–Central Arid Zone Research Institute, Regional Research Station, Pali-Marwar, Rajasthan, India (24°45′ N, 75°50′ E; 225 m above sea level) in 2009–2010, 2010–2011, and 2011–2012 (Years 1, 2, and 3). The daily weather parameters during the experiment are presented in Figure 1, which were recorded in the agro-meteorology situated 150 m from the experimental site. The experimental soil was fine sandy clay loam in texture, mixed hyper-thermic. It belonged to the family Lithic Calciorthids, having a shallow depth of 25–45 cm and an underlying dense layer of murrum (highly calcareous weathered granite fragments coated with lime) up to 10–15 m depth. At the beginning of experimentation, the soil contained 0.37% organic carbon, 82 mg kg⁻¹ alkaline KMnO₄ oxidizable N, 12.9 mg kg⁻¹ Olsen’s extractable P, and 102 mg kg⁻¹ exchangeable K in the upper 30 cm layer. The details of other physio-chemical properties of experimental soil estimated at the beginning of the experiment are mentioned in

Table 1. Physio-chemical properties of experimental soil at the start of the experiment.

Soil Depth (cm)	Soil Texture (%)				pH	Bulk Density (g cm−3)	Volumetric Soil Water Content (%)		Electrical Conductivity (dS m−1)
	Fine Sand	Coarse Sand	Silt	Clay			Field Capacity	Permanent Wilting Point
0–10	29.7	16.6	35.8	17.9	7.6	1.42	17.2	7.1	0.16
10–22	28.0	15.9	36.4	19.7	7.8	1.39	17.2	7.3	0.16
22–34	23.9	14.1	35.8	26.2	7.8	1.36	20.6	10.1	0.15
34–44	22.1	16.0	33.9	28.0	7.8	1.39	18.7	9.1	0.15
44–100	Gravelly clay loam with weathered granite fragments coated with powdery lime

.

2.2. Experimental Details and Agronomic Practices Followed

The field experiment was laid out in a split-plot design during the rainy season, comprising two planting systems (bed planting and conventional planting) in the main plots and a factorial combination of three intercropping systems (sorghum + Sesbania, sorghum + cowpea, sole sorghum) × two crop durations (50 and 60 days) in the sub-plots. During the post-rainy season, Eruca sativa crop was taken on the residual of the rainy season, and each plot was further sub-divided into two for the application of two levels of gypsum (250 kg ha⁻¹ and no gypsum) in a split–split-plot design. An extra treatment of fallow–Eruca sativa (conventional planted) was taken as a control. Experimental details and important agronomic practices followed are mentioned in

Table 2. Experimental details and agronomic practices followed during rainy and post-rainy seasons.

Particulars	Details
Rainy-season cropping
Experimental Design	Split plot
Treatment Combinations	12
Replications	3
Plot Size	Main plot—36.0 m × 4.5 m Sub-plot—6.0 m × 4.5 m
Fertilizer Application	Sorghum—40 kg N + 8.75 kg P ha−1; cowpea—20 kg N + 17.5 kg P ha−1
Crops and Crop Varieties	Sorghum cv ‘CSV 15′; Sesbania cv ‘local’; cowpea cv ‘FS 68′
Sowing Date	July 12, 9, and 16 during Years 1, 2, and 3
Harvesting Date	Sorghum and cowpea—as per treatment; Sesbania—harvesting and incorporation in soil at 35 days after sowing
Post-Rainy-Season Cropping
Experimental Design	Split–split plot with control (contrast)
Treatment Combinations	24 + 1
Replications	3
Plot Size	Main plot and sub-plot—same as in rainy season Sub–sub-plot—6.0 m × 2.0 m
Fertilizer Application	20 kg N + 8.75 kg P ha−1
Crop and Crop Variety	Eruca sativa cv ‘RTM 314’
Sowing Date	October 24 and 22 during Years 2 and 3
Harvesting Date	March 3 and February 25 during Years 2 and 3

.

Before the commencement of rain, the experimental field was opened by a tractor-drawn disc plow. After receiving sufficient rain, it was prepared for sowing with two runs of cultivator and planking. Conventional sowing of rainy-season crops was carried out with a seed cum fertilizer drill at a row spacing of 45 cm. For bed planting treatment, a tractor-drawn seed cum fertilizer bed planter was used to make 37.5 cm wide and 15 cm high beds with 30 cm wide furrows. The crops were sown in two rows on the shoulders of each bed in 2:2 proportions in replacement series as per treatments. Half the dose of nitrogen and a full dose of phosphorus were applied at the time of sowing, and the remaining half dose of nitrogen was applied at 30 DAS (days after sowing). In sorghum + Sesbania treatments, Sesbania was cut, weighed, and incorporated manually into the soil at 35 DAS. As per treatment, crops were harvested manually at 50 and 60 DAS.

Immediately after the harvest of rainy-season crops, the field (including both rainy-season cropped plots as well as fallow plot) was again opened by a tractor-drawn disc harrow, and in mid-October, it was then prepared for the sowing of post-rainy-season crops by two runs of cultivator and planking. Under a bed planting system, fresh beds were prepared, and two rows of Eruca sativa per bed were sown using the bed planter. Under conventional planting, Eruca sativa was sown at a spacing of 45 cm through a seed cum fertilizer drill. After completion of one cropping cycle, the same treatments as applied previously were allotted to plots without changing the layout.

2.3. Measurements

2.3.1. Water and Soil Measurements

Soil water content was measured at the time of sowing of the post-rainy-season crop (Eruca sativa) by the gravimetric method. Samples were taken from the center of each plot at 0–22 cm, 22–44 cm, and 44–90 cm soil depths using a 5 cm diameter core probe. This gravimetric soil water was then converted to volumetric water by multiplying it with the soil bulk density for each depth, as mentioned in Table 1. Then, available soil moisture (ASM) in the 0–90 cm soil profile was determined by subtracting water at the permanent wilting point from the total water content at each sampling interval.

At the end of three cycles of experimentation (March 2012), soil samples were again taken from sub-plots at 0–30 cm soil depth. These were analyzed for soil organic carbon [37], available N [38], and dehydrogenase activity (DHA) [39].

2.3.2. Crop Measurements

Plant height and leaf area index (LAI) of sorghum were measured at the time of harvest. Sorghum and cowpea were harvested manually at 15 cm above ground level, and biomass from net plots (6 m × 4 m) was weighed by electronic balance and estimated as Mg ha⁻¹. Sesbania was cut from the whole plot after 35 days of sowing, weighed by electronic balance, estimated on a per-hectare basis, and then manually incorporated into the respective plots. The biomass of Sesbania was analyzed for N content following the Kjeldahl method [40]. During the post-rainy season, growth and yield parameters of Eruca sativa, i.e., plant height, number of branches, silique, and 1000 grain weight were recorded at harvest for 10 plants per plot and averaged. The seed yield was determined from an area of 12 m² from each sub–sub-plot in all replications by manual harvesting, allowed to dry in the field, threshed mechanically, and estimated as kilograms per hectare.

2.3.3. Competition Indices

The land equivalent ratio (LER) was calculated as:

LER = (Y_ab/Y_aa) + (Y_ba/Y_bb),

where Y_aa and Y_bbare yields as sole crops during the respective crop durations, and Y_ab and Y_ba are yields as intercrop. LER values greater than 1 are considered advantageous [41]. The yield of sole cowpea and Sesbania was taken from the crop grown in plots outside the experimental layout.

Aggressivity is another index that represents a simple measure of how much the relative yield increase in “a” crop is greater than that of “b” crop in an intercropping system [42]. It was calculated as:

A_ab = (Y_ab/Y_aaZ_ab) − (Y_ba/Y_bbZ_ba) and A_ba = (Y_ba/Y_bbZ_ba) − (Y_ab/Y_aaZ_ab),

where Z_ab and Z_ba are the planted proportions of the respective intercrops. A crop having a positive “A” value is considered to be a dominant species in the intercropping system.

2.4. Economics and Statistical Analysis

In order to compare system performance (rainy + post-rainy season), the yields of all the crops were converted to Eruca sativa seed equivalent yield as follows:

Equivalent yield (of × crop) = Y_x × (P_x/P_s or P_t),

where Y_x is the yield of crop X (Mg or kg ha⁻¹), P_x is the price of crop X, and P_s and P_t are the prices of green fodder of rainy-season crops or Eruca sativa as the case may be.

The economic analysis of the data was performed based on the prevailing cost of input/operations and the price of produce in the local market. The cost of cultivation for growing crops included expenditure incurred towards land preparation, seed and sowing, fertilizers and their application, weed management, pest control, incorporation of Sesbania into the soil, harvesting, and threshing of crops. Gross returns were worked out based on the prevailing market prices at the time of harvest as follows: sorghum green fodder per 1000 kg at USD 17.86, 17.86, and 14.29; cowpea green fodder at USD 21.43, 21.43, and 17.86 during September of Years 1, 2 and 3, respectively. Market price for Eruca sativa seeds was USD 375 and 571.4 per 1000 kg during April of Years 2 and 3, respectively. Returns from Eruca sativa stover were not included while calculating returns as it generally had no economic value. Net returns were estimated by deducting the total cost of cultivation from gross returns. Economic rainfall use efficiency, i.e., dollars earned per mm of rainfall received was calculated by dividing the net returns of cropping systems by annual rainfall received in that year [43].

All data were statistically analyzed using standard analysis of variance (ANOVA) as applicable to split- and split–split-plot design with SPSS 11.5 version. The significance of the treatment effects was determined using the F-test. For significant treatments, the critical differences (CDs) between the treatment means were calculated by using the standard error [44]. Statistical comparisons were considered significant at the p = 0.05 level.

3. Results

3.1. Rainfall Distribution

Different rainfall situations were encountered during the three years of experimentation (Figure 2). During Year 1 (2009), rainfall received was 168 mm, which was only 39.6% of the average rainfall of the region (424 mm), and that too within the first fifteen days of the rainy season. During Year 2 (2010), about 385 mm of rainfall was received during the rainy season and an unusual 78.2 mm during the post-rainy season. In Year 3 (2011), about 502 mm of rainfall was received during the rainy season.

3.2. Yield Attributes, Yield, and Competition Behavior of Rainy-Season Crops

Bed planting did not influence the yield attributes and yield of sorghum significantly, but it increased the yield of intercropped cowpea significantly by 26.2 and 38.6% in Years 2 and 3, respectively, compared to conventional planting (

Table 3. Effect of planting system, crop duration, and intercropping systems on sorghum yield attributes and fodder yield of rainy-season crops.

	Sorghum Yield Attributes				Fodder Yield (Mgha−1)
Treatments	Plant Height (cm.)			Leaf Area Index	Sorghum			Cowpea			Total
	Year 1	Year 2	Year 3	(Pooled)	Year 1	Year 2	Year 3	Year 1	Year 2	Year 3	Year 1	Year 2	Year 3
Panting Systems
Bed Planting	108	164	223	4.55	10.26	15.16	25.76	3.72	4.94	7.08	11.50	16.82	28.13
Conventional Planting	100	169	240	4.36	9.06	17.69	28.49	3.24	3.50	4.55	10.13	18.86	29.99
Sem±	1.4	4	5.8	0.1	0.66	0.65	0.77	0.24	0.11	0.12	0.71	0.62	0.74
CD (p = 0.05)	NS	NS	NS	NS	NS	NS	NS	NS	0.75	0.79	NS	NS	NS
Crop Duration
50 Days	88	156	218	3.94	8.46	14.56	24.13	2.70	3.38	4.68	9.37	15.70	25.69
60 Days	120	177	244	4.96	10.85	18.29	30.11	4.23	5.05	6.95	12.27	19.97	32.43
Sem±	1.6	3.1	4.1	0.1	0.55	0.49	0.85	0.25	0.35	0.40	0.53	0.48	0.83
CD (p = 0.05)	4.6	9.1	12.2	0.2	1.62	1.45	2.52	1.00	1.40	1.63	1.56	1.41	2.44
Intercropping Systems
Sole Sorghum	109	175	242	4.65	12.18	21.93	34.88	-	-	-	12.18	21.93	34.88
Sorghum + Sesbania	100	159	216	4.31	7.96	12.95	20.99	-	-	-	7.96	12.95	20.99
Sorghum + Cowpea	103	166	236	4.40	8.84	14.40	25.49	3.48	4.22	5.82	12.32	18.62	31.31
Sem±	1.9	3.8	5.1	0.1	0.67	0.60	1.04				0.65	0.59	1.01
CD (p = 0.05)	5.7	11.1	14.9	0.2	1.98	1.78	3.08				1.91	1.73	2.99

). However, total green fodder yield (sorghum + cowpea fodder) was not significantly improved. Increasing the duration of rainy-season cropping from 50 to 60 days significantly increased the green fodder yield of sorghum by 28.6, 25.6, and 24.9%, cowpea by 32.1, 31.0, and 33.9%, and the combined yield by 30.9, 27.2, and 26.2% during Years 1, 2, and 3, respectively. Sorghum exhibited the highest leaf area index (LAI), plant height, and green fodder yield in its sole stand. Replacement of 50% of the area under sorghum with Sesbania as green manure decreased the green fodder yield of sorghum by 34.6, 40.9, and 39.8% during Years 1, 2, and 3, respectively. The total green biomass of Sesbania produced in this system and incorporated at 35 DAS was 10.05 ± 0.65, 11.25 ± 1.37, and 13.00 ± 0.90 Mg ha⁻¹ with N contents of 2.86, 2.71, and 2.80% (on dry matter basis) during Years 1, 2, and 3, respectively (

Table 4. Biomass harvested at 35 days after sowing and percent N content in Sesbania at the time of harvest under sorghum + Sesbania treatment.

Particulars	Year 1	Year 2	Year 3
Sesbania Biomass (Mg ha−1)	10.05 ± 0.65	11.25 ± 1.37	13.00 ± 0.90
Percent N Content (on dry weight basis)	2.86	2.71	2.80

). In the sorghum + cowpea system, the sorghum fodder yield was 27.4, 34.3, and 26.9% (3.34, 7.53, and 13.89 Mg ha⁻¹) less than sole sorghum during Years 1, 2, and 3, respectively (Table 3). The average fodder yield of intercropped cowpea during these years was 3.48, 4.22, and 5.82 Mg ha⁻¹.The competition behavior of intercrops in the systems is reported in

Table 5. Competition behavior of rainy-season crops under different intercropping systems.

Treatments	Year 1			Year 2			Year 3
	Sorghum	Intercrop	System	Sorghum	Intercrop	System	Sorghum	Intercrop	System
Land Equivalent Ratio (LER)
Sole Sorghum	1.00 b	-	1.00 b	1.00 b	0.00	1.00	1.00 b	-	1.00 b
Sorghum + Sesbania	0.66 a	0.57 a	1.23 a	0.60 a	0.52 a	1.12 a	0.60 a	0.57 a	1.17 a
Sorghum + Cowpea	0.78 a	0.51 b	1.28 a	0.66 a	0.53 a	1.19 a	0.73 a	0.52 b	1.25 a
Aggressivity
Sorghum + Sesbania	0.19 a	−0.19 a		0.17 a	−0.17 a		0.07 a	−0.07 a
Sorghum + Cowpea	0.53 b	−0.53 b		0.28 a	−0.28 a		0.40 a	−0.40 a

Figures in each column with the same alphabet in the superscript do not differ significantly.

. The land equivalent ratio (LER) in these systems was greater than unity. The sorghum had a positive aggressivity value compared to negative values for its legume counterparts, i.e., Sesbania and cowpea.

3.3. Available Soil Moisture (ASM) at Sowing of Eruca Sativa

The available soil moisture (ASM) at sowing of the Eruca sativa crop was not significantly influenced by the bed planting system. Increasing the duration of rainy-season crops from 50 to 60 days significantly decreased the ASM during two out of three years of experimentation (Years 1 and 2). Amongst the fallow replacement intercropping systems, the highest ASM was recorded in the residual sorghum + Sesbania system, while sole sorghum had the significantly lowest ASM. When averaged over the treatments, replacement of fallow with cropping during the rainy season significantly reduced the ASM at sowing of the Eruca sativa crop by 22.8, 8.3, and 14.8% compared to fallowing during Years 1, 2, and 3, respectively. During Year 1, ASM measured in the third week of October (the optimum date for sowing Eruca sativa) was found insufficient for germination of Eruca sativa even in the fallow system (

Table 6. Effect of planting systems, crop duration, and intercropping systems during rainy season on available soil moisture at sowing of post-rainy-season Eruca sativa crop.

Treatments	Available Soil Moisture at Sowing of Eruca sativa (mm)
	Year 1	Year 2	Year 3
Planting Systems
Bed Planting	28	78	64
Conventional Planting	26	75	58
Sem±	0.86	1.6	2.1
CD (p = 0.05)	NS	NS	NS
Crop Duration (Rainy Season)
50 Days	30	78	64
60 Days	25	74	57
Sem±	0.76	2.1	1.3
CD (p = 0.05)	2.24	NS	3.8
Intercropping Systems (Rainy Season)
Sole Sorghum	23	69	53
Sorghum + Sesbania	32	79	67
Sorghum + Cowpea	28	80	61
Sem±	0.93	2.5	1.6
CD (p = 0.05)	2.75	7.5	4.7
Contrast
Fallow–Eruca sativa	35	83	71
Rest	27	76	61
‘F’ test	Sig.	Sig.	Sig.

).

3.4. Yield Attributes and Yield of Post-Rainy-Season Crop (Eruca Sativa)

Amongst the planting systems, bed planting resulted in significantly higher values of yield attributes of Eruca sativa, i.e., silique per plant, during both years (Years 2 and 3) and 1000 seed weight during Year 2. However, these improvements in yield could not manifest into increased seed yield at significant levels over conventional planting (

Table 7. Effect of planting system, residuals of rainy-season cropping and gypsum application on yield attributes of Eruca sativa.

Treatments	Eruca sativa
	Plant Height (cm)		Silique/Plant		1000 Seed Weight (g)
	Year 2	Year 3	Year 2	Year 3	Year 2	Year 3
Planting Systems
Bed Planting	104	70	135.5	71.4	3.65	3.05
Conventional Planting	100	61	115.8	53.1	3.33	2.68
Sem±	2.4	1.0	3.2	2.8	0.04	0.07
CD (p = 0.05)	NS	6.0	19.6	17.3	0.27	NS
Crop Duration (Rainy Season)
50 Days	103	65	127.4	63.3	3.58	3.05
60 Days	101	65	123.9	61.3	3.40	2.68
Sem±	1.5	1.6	3.7	1.8	0.07	0.08
CD (p = 0.05)	NS	NS	NS	NS	NS	0.24
Intercropping Systems (Rainy Season)
Sole Sorghum	100	67	106.1	53.8	3.23	2.69
Sorghum + Sesbania	104	65	145.9	66.2	3.63	3.06
Sorghum + Cowpea	102	64	125.0	66.8	3.60	2.84
Sem±	1.8	1.9	4.6	2.2	0.08	0.10
CD (p = 0.05)	NS	NS	13.5	6.4	0.24	0.29
Gypsum (applied to Eruca sativa)
Gypsum at 250 kg ha−1	105	68	130.9	65.5	3.84	3.05
No Gypsum	99	62	120.4	59.1	3.14	2.68
Sem±	1.2	1.1	3.6	1.8	0.04	0.03
CD (p = 0.05)	3.4	3.1	10.4	5.1	0.12	0.09
Contrast
Fallow–Eruca sativa	105	64	133.0	120.0
Rest	102	66	125.4	91.3
‘F’ test	NS	NS	Sig.	Sig.

and

Table 8. Effect of planting system, residuals of rainy-season cropping, and gypsum application on seed yield of post-rainy-season Eruca sativa and system productivity.

Treatments	Post-Rainy-Season Productivity (Eruca sativa Seed Yield, kg ha−1)			System Productivity (Rainy + Post-Rainy) (as Eruca sativa Seed Equivalent Yield, kg ha−1)
	Year 1	Year 2	Year 3	Year 1	Year 2	Year 3
Planting System
Bed Planting	-	1002	485	559	1818	1203
Conventional Planting	-	933	424	493	1842	1184
Sem±		23	11	34	53	27
CD (p = 0.05)		NS	NS	NS	NS	NS
Crop Duration (Rainy Season)
50 Days	-	1027	486	455	1785	1138
60 Days	-	908	423	597	1875	1248
Sem±		20	13	25	31	26
CD (p = 0.05)		59	0.37	74	NS	76
Intercropping Systems (Rainy Season)
Sole Sorghum	-	940	425	580	1984	1297
Sorghum + Sesbania	-	1023	489	379	1640	1014
Sorghum + Cowpea	-	940	449	619	1866	1268
Sem±		24	15	31	39	31
CD (p = 0.05)		72	46	91	114	93
Gypsum (applied to Eruca sativa)
Gypsum at 250 kg ha−1	-	1070	486	-	1932	1224
No gypsum	-	865	423	-	1728	1162
Sem+		11	05		11	05
CD (p = 0.05)		33	14		33	14
Contrast
Fallow–Eruca sativa	-	1160	653	00	1160	653
Rest	-	968	454	526	1830	1194
‘F’ test		Sig.	Sig.	-	Sig.	Sig.

). Increasing the duration of the rainy-season crop by 10 days (i.e., 50 to 60 days) decreased the yield attributes and consequently the seed yield of Eruca sativa by 11.6% and 8.0% during Years 2 and 3, respectively. Sorghum + Sesbania system in the rainy season resulted in significantly higher yield attributes and seed yield of Eruca sativa compared to sole sorghum and sorghum + cowpea. Soil application of gypsum at 250 kg ha⁻¹ to Eruca sativa crop significantly improved yield attributes, i.e., branches per plant, silique per plant, 1000 seed weight, and finally seed yield by 9.5% and 23.7% over control during Years 2 and 3, respectively.

Averaged over the treatments, fallow replacement during the rainy season significantly reduced the seed yield of the succeeding Eruca sativa crop. The average reduction over the fallow–Eruca sativa system was 16.5% and 30.4% during Years 2 and 3, respectively.

3.5. System Productivity, Economics, and Rainfall Use Efficiency

Bed planting did not show its superiority over conventional planting in any of the economic parameters studied (Table 8 and

Table 9. Economics and rainfall use efficiency of cropping systems as influenced by fallow replacement and post-rainy-season cropping.

Treatments	Cost of Cultivation (Pooled, USD ha−1)		Net Returns (USD ha−1)									Economic Rainfall Use Efficiency (USD ha−1 mm−1)
	Rainy	Post-Rainy	Rainy Season			Post-Rainy Season						Rainy + Post-Rainy
			Year 1	Year 2	Year 3	Year 1	Year 2	Year 3	Year 1	Year 2	Year 3	Year 1	Year 2	Year 3
Planting Systems
Bed Planting	165.7	138.6	68.8	141.2	218.8	-	247.6	128.0	68.8	388.8	346.8	0.41	0.84	0.60
Conventional Planting	159.5	131.9	49.2	182.2	249.8	-	227.8	100.4	49.2	410.0	350.2	0.29	0.89	0.60
Sem±			12.9	11.1	10.3		8.6	6.2	12.9	19.7	15.5	0.08	0.04	0.03
CD (p = 0.05)			NS	NS	NS		NS	NS	NS	NS	NS	NS	NS	NS
Crop Duration (Rainy Season)
50 Days	158.3	135.3	36.7	127.1	190.7	-	260.0	132.0	36.7	387.1	322.7	0.22	0.84	0.56
60 Days	166.9	135.3	81.3	196.3	277.9	-	215.4	96.4	81.3	411.7	374.3	0.49	0.89	0.64
Sem±			9.4	8.5	11.8	-	7.5	7.2	9.4	11.8	14.7	0.06	0.03	0.03
CD (p = 0.05)			27.8	25.0	34.7		22.0	21.3	27.8	NS	43.3	0.17	0.08	0.07
Intercropping Systems (Rainy Season)
Sole Sorghum	168.5	135.3	62.2	224.4	304.1	-	227.2	97.5	62.2	451.6	401.6	0.37	0.98	0.69
Sorghum + Sesbania	158.3	135.3	16.8	73.1	115.8	-	258.5	133.7	16.8	331.6	249.5	0.10	0.72	0.43
Sorghum + Cowpea	161.0	135.3	98.0	187.6	283.0	-	227.4	111.4	98.0	415.0	381.0	0.58	0.90	0.68
Sem±			11.5	10.4	14.4		9.1	8.8	11.5	14.4	18.0	0.07	0.03	0.03
CD (p = 0.05)			34.0	30.7	42.5		26.9	26.1	34.0	42.6	53.0	0.20	0.09	0.09
Gypsum (applied to Eruca sativa)
Gypsum at 250 kg ha−1	-	139.5	-	-	-	-	272.1	127.6		433.8	361.8	-	0.94	0.62
No gypsum	-	131.1	-	-	-	-	203.2	100.8		364.9	335.2	-	0.79	0.58
Sem+										4.2	2.8		0.01	0.01
CD (p = 0.05)										12.3	8.1		0.03	0.02
Contrast
Fallow–Eruca sativa	-	141.2	-	-	-	-	304.3	221.5	-	304.3	221.5	-	0.66	0.38
Rest	-	135.3	58.7	106.4	234.3	58.7	237.7	114.2	59.0	399.4	348.5	0.36	0.87	0.60
‘F’ test		NS					Sig.	Sig.		Sig.	Sig.		Sig.	Sig.

). Extending the crop duration of rainy-season cropping from 50 to 60 days increased the system productivity and system net returns by 21.5 and 15.9%, respectively, during Years 2 and 3 (Table 8). Compared to the sole sorghum–Eruca sativa system, the system productivity of the sorghum + cowpea–Eruca sativa system was at par during two years of experimentation. Replacing 50% of the sorghum stand with a green manure crop (Sesbania) resulted in significantly less system productivity, net returns, and rainfall use efficiency. Gypsum application further improved the net returns of Eruca sativa by 33.9 and 26.6%, respectively, during Years 2 and 3.

When averaged over the treatments, fallow replacement with rainy-season cropping increased the system productivity by 57.7% and 82.8% during Years 2 and 3, respectively. The rainy-season cropping provided fodder equivalent to 526 kg ha⁻¹ Eruca sativa seed and net returns of 59.0 USD ha⁻¹. Rainy-season cropping reduced the net returns from Eruca sativa crop by 21.9 and 48%, but additional returns from them improved the system net returns by 31.2 and 57.3% during Years 2 and 3, respectively. There was a corresponding improvement in rainfall use efficiency in the fallow replacement system. It was 0.36, 0.87, and 0.60 USD mm⁻¹ ha⁻¹ under the fallow replacement–Eruca sativa system and 0, 0.66, and 0.38 USD mm⁻¹ ha⁻¹ rainfall under the fallow–Eruca sativa system during Years 1, 2, and 3, respectively.

3.6. Soil Fertility Status

After completion of the three cropping system cycles, soil under bed planting had significantly higher available N and dehydrogenase activity than the conventional system (

Table 10. Effect of planting systems, crop duration, and intercropping systems on soil properties measured at the end of three cropping cycles (April 2012).

Treatments	Soil Organic Carbon (%)	Available N (mg g−1 soil)	Available P (kg ha−1)	Dehydrogenase Activity (µg tpf g−1 hr−1)
Planting System
Bed Planting	0.39	81.29	12.94	9.45
Conventional Planting	0.37	78.22	12.06	7.46
Sem±	0.01	0.35	0.23	0.19
CD (p = 0.05)	NS	2.14	NS	1.18
Crop Duration (Rainy Season)
50 Days	0.38	83.13	13.14	8.54
60 Days	0.38	76.39	11.86	8.37
Sem±	0.01	1.67	0.23	0.22
CD (p = 0.05)	NS	4.94	0.68	NS
Intercropping System (Rainy Season)
Sole Sorghum	0.36	68.42	11.77	6.57
Sorghum + Sesbania	0.40	94.44	13.65	10.37
Sorghum + Cowpea	0.37	76.42	12.08	8.43
Sem±	0.01	2.05	0.28	0.27
CD (p = 0.05)	0.02	6.05	0.83	0.79
Contrast
Fallow–Eruca sativa	0.36	87.30	10.93	6.91
Rest	0.38	79.76	11.81	8.46
‘F’ test	Sig.	Sig.	NS	Sig.

). The longer crop duration (60 days) of fallow replacement crops significantly reduced available N and P in the soil. All the soil health parameters tested, i.e., SOC, available N, P, and dehydrogenase activity (DHA), improved significantly under the sorghum + Sesbania intercropping system, followed by sorghum + cowpea. Utilization of fallows for rainy-season cropping significantly increased the soil organic carbon (SOC) and dehydrogenase activity (DHA). However, the soil N was higher in the fallow–Eruca sativa system.

4. Discussion

The productivity of post-rainy-season crops was found to be strongly related to the extent of moisture conserved in the soil profile, as also evidenced by the reviewed literature [2,10,11,14]. The linear function of available soil moisture at sowing of Eruca sativa explained 31% of the variability in Eruca sativa grain yield during Year 2 and 64% during Year 3 (Figure 3). The temporal variation in response was due to the fact that during Year 2, the Eruca sativa crop received unusual rainfall (78.2 mm) in the second fortnight of November and few showers during the last week of December (Figure 2). It had overshadowed the effect of stored soil moisture measured at the sowing of the crop. On critical analysis of rainfall pattern vis a vis available soil moisture (ASM) at sowing of Eruca sativa, it was observed that ASM was more dependent on the quantum of rainfall received during the second half of the rainy season. For example, the total rainfall received was higher during Year 2 but the ASM was higher during Year 3 (e.g., 17% higher in fallow plots, Table 6). This could be understood from the fact that the rainfall received during the second half of the rainy season (i.e., 50 days after sowing of rainy-season crops) was higher during 2011(164.8 and 99.7 mm during Years 2 and 3, respectively). The soil moisture stored during the initial rains was exposed to evaporation and percolation losses for a longer duration which are much higher in an arid environment [46]. This confirms our hypothesis that the efficiency of soil moisture storage is higher from later rains, and hence initial rains could be utilized for the production of biomass in the current season. For efficient utilization of this pattern, it was important to select suitable rainy-season crops, their duration, and other agronomic practices.

Since the stover of Eruca sativa is non-edible, fodder crops sorghum in sole standand intercropped with legumes (Sesbania aculeata as green manure and cowpea as fodder) in the 2:2 proportion were tested. Sole sorghum produced maximum fodder, but the opportunity cost in terms of yield penalty in succeeding Eruca sativa crop was highest. This was mainly due to the reduction in available soil moisture stored in soil profile, soil fertility (available N and P), and biological activity (DHA) (Table 6 and Table 10). The competitive behavior of sorghum and legumes as intercrops indicated that sorghum was the dominant species (having positive aggressivity value) in sorghum–legume intercropping (Table 5). However, legumes have shown complementarities with sorghum, as indicated by LER values greater than unity. This might be due to improved nitrogen supply to sorghum from legume counterparts and better utilization of space due to differential plant architecture [28,47,48]. In the sorghum + Sesbania system, a significant amount of nitrogen-rich green biomass (2.71–2.86% N on dry weight basis) was added through green manuring of intercropped Sesbania (10.05–13.90 Mg ha⁻¹), and hence the highest SOC, available N, and DHA were measured after completion of three cropping cycles. This system also showed the highest ASM, because the field was half vacated after 35 days of sowing due to harvesting and incorporation of Sesbania, leading to less consumption of moisture per unit basis for the rest of the period. This resulted in an increased yield of the succeeding Eruca sativa crop by 8.8 and 15% over sole sorghum during Years 2 and 3, respectively, but it could not compensate for the fodder yield loss due to the utilization of 50% of the area for growing the green manure crop under the intercropping system during the rainy season. The sorghum + cowpea intercropping system appeared to be the optimum crop combination. Although the forage production potential of cowpea was less, it adequately compensated for the system productivity and profitability through a higher market price for more nutritious sorghum + cowpea mixed forage and yield improvements in succeeding Eruca sativa crop [32]. Though the above-ground biomass of cowpea was removed at harvest, stubbles were incorporated into the field. As the roots and rhizodeposits of legumes are rich in N [49,50,51]. The N-enriched compounds entering the soil are prone to mineralization and stimulate microbial activity, providing additional nitrate availability to succeeding Eruca sativa [50,52].

Increasing the duration of rainy-season cropping by a mere 10 days (i.e., from 50 to 60 days) improved the yields of fallow replacement crops by 25–34% but decreased the seed yield of succeeding Eruca sativa crop by 11–13% only, resulting in significantly higher system productivity, net returns, and rainfall use efficiency.

We further tried to improve the productivity of Eruca sativa through better nutrient management practices. Oilseed crops have a high demand for sulfur, with approximately 16 kg of sulfur required to produce 1 ton of seeds containing 91% dry matter [34,53]. A strong interaction between sulfur and nitrogen for seed and oil production in oilseed crops has been reported [36,54]. Hence, we applied sulfur to this oil seed crop (Eruca sativa) through a cheaper and easily available source, i.e., gypsum at 250 kg ha⁻¹, and it significantly improved the yield by 16.5–30.4%.

When averaged over treatments, fallow replacement reduced the available soil moisture at the sowing of Eruca sativa by 8.3–22.8% and its yield by 16.5–30.4% compared to the fallow–Eruca sativa system. By sacrificing this production, an additional rainy-season fodder crop was successfully grown, thus improving the system productivity by 57.7–82.8%, net returns by 31.2–57.3%, and rainfall use efficiency by 0.21–36 USD mm⁻¹ ha⁻¹. This system also indicated the potential to impart resilience to arid zone farming and judicious utilization of meager rainfall. For example, in this experiment, the rainfall received during Year 1 was only 168 mm (44% of normal rainfall), and hence the stored soil moisture was not sufficient to grow Eruca sativa. This implies that under the traditional fallow–Eruca sativa system, there would be complete crop failure with no production for one whole year. Mean while, in the fallow replacement system, there was a fodder production equivalent to 5.6 q ha⁻¹ and net returns of 49 USD ha⁻¹ from rainy-season cropping. Similarly, during Year 2, unusual rainfall during winters was effectively realized for yield gains of the Eruca sativa crop. The opportunity would have otherwise been lost if only rainy-season crops were taken. During Year 3, when rainfall was normal with respect to quantum and distribution, the dual cropping system improved the system productivity by 1.83 times and net returns by 1.57 times over the fallow–Eruca sativa system. This strategy of utilizing the rains for dual cropping appears more environmentally friendly as well. Fallowing systems improve the nutrient availability (especially N) mainly through ‘mining’ the soil and accelerating the depletion of the soil organic matter, as evident from the significantly lower OC content as measured after three cropping cycles [2]. By contrast, improvement in soil N status under a fallow replacement system could be attributed to environmentally friendly biological fixation in the roots of legumes and the addition of N-rich biomass as crop residue or green manure into the soil [55].

5. Conclusions

Through this experiment, we may conclude that fallow replacement and cropping intensification in drylands is a solution for the efficient use of rainfall and provides an opportunity to fulfill the additional demands for agricultural produce without exploring new farmlands. In arid regions of India, initial rains can be utilized for growing fodder sorghum + cowpea for a duration of sixty days, and later rains can replenish profile soil moisture even in Lithic Calciorthids soils having a shallow depth of 25–45 cm only that could be used for growing the drought-hardy Eruca sativa crop. Gypsum application of 250 kg per hectare is recommended for the Eruca sativa crop. This is one possibility of utilizing fallows in arid environments. Similar opportunities with different sets of crops and strategies need to be explored for utilizing fallow under different environments, as the scope for putting more land under agriculture is limited. Such strategies for fallow replacement are region-specific; hence, more such studies should be undertaken in other ecologies as well. They should also take into account the environmental issues related to fallowing.