Evaluation of Organic Weed Management Practices on Growth, Yield and Weed Control Efficiency in Soybean-chickpea Sequence under Irrigated Condition  

Soybean-chickpea is important cropping sequence adopted in Maharashtra State under irrigated condition. The area under soybean-chickpea cropping sequence in Maharashtra State is 5.20 lakh hectares (Anonymous, 2017). Soybean-chickpea cropping sequence faces severe weed competition during the early stages of crop growth resulting loss of 40 to 60% potential yield in soybean and up to 68% in chickpea crop (Mishra et al., 2002, Kumar et al., 2014).
       
Weeds are widely reported as a key constraint in organic agriculture. Farmers have struggled with the presence of weeds in their fields since the beginning of agriculture. Higher infestation of weeds in crop tends to decrease crop yield by increasing competition for water, sunlight and nutrients while serving as host plants for pests and diseases. Today, widespread use of herbicides has resulted in purporated environmental and health problem as well as residual problems to succeeding crops. It has also been found that in some cases herbicide use can cause some weed species to dominate fields because the weeds develop resistance to herbicides. In addition some herbicides are capable of destroying weeds that are harmless to crops resulting in potential decrease in biodiversity on farm (Patel et al., 2013).
       
In organic farming cultural and mechanical methods are necessary to break the weed cycle. In Marathwada region of Maharashtra state no any research work carried out on organic weed management in soybean-chickpea cropping sequence. Weed management is a serious problem in both the crop and it mostly controlled through chemical weed control. Now a days residue free food requirement is high. So, keeping this point in view present investigation was carried out to evaluate the cultural and mechanical weed management practices in soybean-chickpea cropping sequence on growth, yield and weed control under organic production system.

A field experiment was conducted at Experimental Farm of AICRP on Integrated Farming System, Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani (MS) during Kharif and Rabi seasons of 2017-18 and 2018-19.
       
The study involved ten treatments were T₁-Two hand weeding at 20-25 and 45-50 DAS, T₂-One hoeing 20-25 DAS + one hand weeding at 45-50 DAS, T₃ - Soybean + Sunhemp incorporation after 35-40 DAS in kharif season and Chickpea + Safflower (2:1) in rabi season,  T₄-Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS, T₅- Soil mulch at the time of sowing + one hand pulling at 25 DAS, T₆- Incorporation of neem cake 1.5 tonne/ ha 15 days before sowing + one hand  weeding at 25 DAS, T₇-Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS, T₈-Mulching with straw, T₉- Weed free and T_10- Weedy check which were evaluated in randomized block design with three replications. The experimental plots were 8.10 m wide and 5.5 m long laid out according to randomized block design with each treatment replicated thrice. The observation on weed density and weed dry matter were taken randomly from 1m² quadrat from net plot area from each treatment. Same were harvested and then oven dried for 48 hours at 70oC. Weed control efficiency (WCE) was calculated by using formula  
Where,
WCE = Weed control efficiency in percent
DWC = Weed dry weight in control plot.
DWT = Weed dry weight in treated plot.
The soybean equivalent yield was calculated by the following formulae for both the years.

Weed flora
 
During both the years of investigation.the predominant weed flora in soybean crop were Cynodon dactylon, Brachiria eruciformis, Commelina benghalensis, Cyperus rotundus, Phyllanthus niruri, Parthenium hysterophorus and Euphorbia geniculata. The predominant weed flora in chickpea crop were Cynodon dactylon, Cyperus rotundus, Phyllanthus niruri, Convolvulus arvensis and Amaranthus viridis. Weed density of monocot, dicot and total weeds at 40 days after sowing in soybean and chickpea given in Table 1 and 3 respectively.
 

 

 
Effect on weeds
Soybean
 
Treatment T₉ (Weed free) recorded lowest weed density of both monocot and dicot weeds followed by T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) at 40 DAS during both the year study. The higher weed density observed in T₁₀ (weedy check) (Table 1). Similar trend was observed in case of dry weight of both monocot and dicot weeds (Table 2). Highest weed control efficiency recorded by T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) at 40 DAS during both the year study (Table 5).
 

 

 
Chickpea
 
During both the year study, at 40 DAS the lowest weed density of  both monocot and dicot weeds was recorded by treatment T₉ (weed free) followed by T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS). The higher weed density observed in T₁₀ (weedy check) (Table 3). Similar trend was observed in case of dry weight of both monocot and dicot weeds (Table 4). Highest weed control efficiency recorded by T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) at 40 DAS during both the year study (Table 5).
 

 
Effect of organic weed management practices on growth and growth characters
 
Soybean
 
During both the year study, treatment T₄ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS) recorded highest plant height which was at par with treatment T₃ (Soybean + Sunhemp incorporation after 35-40 DAS) and significantly superior to rest of the weed management practices. Significantly lower plant height was observed under T₁₀ (Weedy check) treatment shown in Table 6.
 

       
Significantly higher growth characters per plant viz number of functional leaves, maximum number of branches; maximum number of pods and dry matter accumulation at harvest were recorded by weed free (T₉) treatment. It was at par with T₁ (Two hand weeding at 20-25 and 45-50 DAS) and T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) and recorded significantly higher growth characters of soybean as compared to rest of the treatments shown in Table 6. This is due to reduction in weed growth at critical crop growth stages by two hand weeding and weed free resulted in good aeration and nutrient availability to crop growth. It might be due to overall favorable growth and more photosynthesis. Similar results were reported by Bali et al., (2016). This is also due to failure of weeds germination as a result of no or less supply of oxygen due to soil solarization. Similar results were reported by Ahmad et al., (2015) and Sharma et al., (2016).
 
Chickpea
 
Application of T₄ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS)  and  T₃ -Gram + Safflower (2:1) were found equally effective in increasing plant height but significantly superior to rest of the weed management practices. Significantly lower plant height was observed under T₁₀ (Weedy check) treatment during both the year study given in Table 7. 
 

       
During both the year, significantly maximum number of functional leaves, number of branches per plant , maximum number of pods per plant and dry matter accumulation per plant at harvest were noticed by T₉ (weed free) treatment. It was at par with T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) and T₆ (Incorporation of neem cake 1.5 tonne/ ha 15 days before sowing + one hand weeding at 25 DAS) and found significantly superior over rest of the treatments. Lower values of growth character observed in T₁₀ (Weedy check) during both the year study presented in Table 7.
 
Effect of organic weed management practices on yield
 
Soybean
 
Data on seed yield of soybean (kg ha^-1) during first and second year along with pooled analysis are tabulated in Table 8. During first year, treatment T⁴ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS) recorded significantly more seed yield (2541 kg ha^-1) was on par with T⁹ (weed free) i.e. 2417 kg ha^-1 and T¹ (Two hand weeding at 20-25 and 45-50 DAS) treatment i.e. 2370 kg ha^-1 and it was significantly superior over rest of the weed control treatments. Similar trend was observed in second year and pooled analysis. It might be due to reduced population of weeds at initial stage due to stale seed bed and suppression of weed growth due to higher plant density by reduced spacing. Lower seed yield (1150 kg ha^-1) was noticed with T¹⁰ (weedy check) treatment. It was due to heavy infestation of weeds and suppresses the crop growth thus causing reduced yield. These finding are in agreement with results of Sanbagavalli et al., (2016) and Peer et al., (2013).
 

 
Chickpea
 
All the weed control treatments were found to be significantly superior over the weedy check treatment during both the year shown in Table 8. During first year, treatment (T³) Chickpea + Safflower (2:1) recorded significantly more seed yield (2771 kg ha^-1) which was at par with T⁴ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS), T⁹ (Weed free), T⁷ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS)  and T₆ (Incorporation of neem cake 1.5 tonne/ ha 15 days before sowing + one hand weeding at 25 DAS) treatments and significantly superior over rest of the treatments.
 
       
During second year, (T3) Chickpea + Safflower (2:1) treatment recorded significantly more grain yield (2471 kg ha^-1) which was at par with T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) , T₆ (Incorporation of neem cake 1.5 tonne/ ha 15 days before sowing + one hand weeding at 25 DAS), T₉ (Weed free), T₄ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS) and T₁ (Two hand weeding at 20-25 and 45-50 DAS) treatments and significantly superior over rest of the treatments. In pooled data, more seed yield was recorded by (T₃) Chickpea + Safflower (2:1) treatment (2621 kg ha^-1) which on par with T₄ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS), T₉ (Weed free), T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) , T₆ (Incorporation of neem cake 1.5 tonne/ ha 15 days before sowing + one hand weeding at 25 DAS) and T₁ (Two hand weeding at 20-25 and 45-50 DAS) treatments. It might be attributed to lesser competition offered by weeds for light, water and nutrients which resulted in more uptake of nutrients and produced more photosynthates. Lower yield was noticed with T₁₀ (Weedy check) treatment during both the years and in pooled result. This is due to more weed competition with crop for light, water and nutrients produced less photosynthates. Similar results reported by Rathod et al., (2017) and Pedde et al., (2013), Singh and Jain (2017) and Bhutada and Bhale (2015).
 
Soybean equivalent yield (SEY Kg ha^-1) of soybean-chickpea cropping system
 
During 2017-18, higher soybean equivalent yield of system was recorded by T₄ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS) treatment (5766 kg ha^-1) which was at par with T₃ (Chickpea + Safflower) (2:1), T₉ (Weed free), T₁ (Two hand weeding at 20-25 and 45-50 DAS), T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS) and T₆ (Incorporation of neem cake 1.5 tonne/ ha 15 days before sowing + one hand weeding at 25 DAS) and significantly superior over rest of the treatments. Lower soybean equivalent yield was observed with T₁₀ (Weedy check) treatment (3088 kg ha^-1). During 2018-19, T₄ (Stale seed bed + reduced spacing + 2 tonne of wheat straw + one hand weeding at 25 DAS) treatment recorded higher soybean equivalent yield of system ( 6021 kg ha^-1) which was at par with T₉ (Weed free), T₃ (Chickpea + Safflower) (2:1), T₇ (Soil solarization with 25 μ polythene mulch during summer + one hand weeding at 25 DAS), T₁ (Two hand weeding at 20-25 and 45-50 DAS) and T₆ (Incorporation of neem cake 1.5 tonne/ ha 15 days before sowing + one hand weeding at 25 DAS) treatments and found significantly superior over rest of the treatments. Lower soybean equivalent yield was observed with T₁₀ (weedy check) treatment (2812 kg ha^-1). Similar kind of trend was observed in pooled analysis shown in Table 8.