Alternative integrated weed control with cowpea to improve soil properties

Cover crop (CC) is a ground cover plant. This is one of the strategies to improve soil quality and suppress the use of herbicides. One of the CC is able to survive in a tropical climate and grows well in soil conditions with moderate to low fertility is cowpea. Therefore, this study attempts to examine the benefits of using cowpea as CC to improve soil quality. This research will be conducted with the experimental method. Moreover, this study used a randomized block design with 2 factorials. The first factor was weed control techniques (P), with levels: without weed control (P0), cover crop (P1), pre-emergence herbicides (P2), post-emergence herbicides (P3), and weed-free (by weeding) (P4). And the second factor is tillage technique (T), namely: without tillage (T0) and conventional tillage (T1). Based on the research conducted, it was found that the combination of using CC (P1) and no tillage (T0) treatments were able to improve soil quality, (P1) affects the nitrogen value of the soil due to the presence of root nodules. While the tillage technique (T0) affects the bulk density (BD) which tends to be stable, and the organic-C content is quite restrained due to no evaporation due to tillage.


Introduction
Weed control using herbicides has received attention because it is considered to have an effect on human health, biodiversity, and sustainable agricultural land due to the toxic chemicals in herbicides.Therefore, the European Union began targeting the EU Green Deal to reduce the use of pesticides, including herbicides at approximately 50% in 2030.This is to achieve a resilient and sustainable agricultural system [1].In addition, using the same type of herbicide repeatedly over a long period of time can lead to herbicide resistance [2].Based on this moment, we need a strategy to reduce the use of herbicides, without reducing the productivity of agricultural land.
Integrated weed control is one of the efforts to do.Integrated weed control is a component of a sustainable agroecosystem [3].Thus, non-chemical integrated weed management includes new cultivation techniques (intercropping, false nurseries, land reduction, crop rotation, and diversification, adjustment of density and planting date), non-chemical tools (burning, seed coating, beneficial microorganisms, mechanical weeding, biocontrol agents and natural herbicides), competitive plant materials (hybrids and cultivars, cover crops, service crops), and new technologies and precision farming tools (Decision Support Systems, robots, remote sensing, UAV, omics, and nanotechnology) [1].
However, cover crop (CC) as a way of integrated weed control based on competitive plant materials, by suppressing weed emergence on the soil surface.Weed control using CC can be carried out when CC is still actively growing and developing or when its growth period has ended, namely by forming mulch from CC biomass [3].Several CC suppresses the emergence of weeds in the presence of mulch cover 1230 (2023) 012058 IOP Publishing doi:10.1088/1755-1315/1230/1/012058 2 and some of them have allelopathic substances [4].
Cover crop (CC) has a multifunctional role.The role of CC as a suppressor of weed growth and also improving soil quality.According to [5], CC can help improve the physical, biological, and chemical characteristics of the soil.Improving soil quality in question includes soil structure, soil erosion control, and water absorption [6], as well as increasing soil nutrients from the decomposition of CC biomass.One of the plants that can be used as CC is cowpea (Vigna unguiculata).Some of the advantages of this cowpea plant as CC are that it can grow well in tropical climates, and on soils with moderate to low fertility [5].Cowpea (Vigna unguiculata Walp.) is increasingly planted as a second season crop in some region.The impact of cowpea inoculation with recommended rhizobium strains on biological nitrogen fixation (BNF) and grain yield [7].
Similarly, improving soil quality with the use of CC is expected to be able to help reduce the intensification of tillage on agricultural land.Intensification of conventional tillage can reduce soil quality, such as decreased biological activity and biodiversity (especially natural enemies of pests and weed seeds), increased soil erosion, damage to soil structure, loss of organic matter, and leaching of nutrients [8,9].This affects sustainable agricultural land.In addition, the intensification of tillage can also provide a great opportunity for seed banks stored in the soil to rise above the soil surface and they can germinate.Based on the description above, it is necessary to carry out activities to study the use of cowpea as a cover crop for alternative integrated weed control to improve soil quality to support sustainable agriculture.

Time and place
This research was conducted from July to December 2022 in UPT Palawija and Horticulture Tanjung Selamat, Pancur Batu District.

Tools and materials
This research used electric knapsack sprayers, measuring cups, tripe, hoes, tape measure, cutter, treatment stick, analytical scales, plastic sample, stationery, and cameras.Besides, the materials used in this study were cowpea seeds (Vigna unguiculata) as a cover crop, with white seeds and black eye pea (Albina IPB) varieties, pre-emergance herbicides with pendimethalin active ingredient, post-emergance herbicides with active ingredients of topramezone and atrazine.

Land preparation.
Land preparation was carried out by measuring using a tape measure and making stakes for each treatment plot.The size of each plot is 2.1 x 1.4 m. the distance between plots is 50 cm and the distance between blocks is 100 cm.In this plot, corn seeds will be planted with a spacing of 70 x 20 cm and cowpea seeds with a spacing of 40 x 10 cm.

Soil analysis I.
Soil analysis I was carried out before the treatment of both weed control techniques (P) and land management techniques (T) was carried out.Samples for this soil analysis were taken by random sampling and then composited from the study area with a depth of 0-20 cm using a hoe.Parameters to be analyzed included pH H 2O, Organic-C, total-N, available-P, bulk density, CEC, total microbes.1230 (2023) 012058 IOP Publishing doi:10.1088/1755-1315/1230/1/0120583 2.3.3.Soil processing.Soil tillage is manually using a hoe on conventional tillage treatment plots.The depth of tillage is 15 cm.The treatment of pre-emergence herbicide application and tillage, tillage activities are carried out when the cover crop has begun to be terminated.

Cover crop (CC) planting.
The type of CC used is cowpea or also called cowpea.The cowpea variety used was Albina IPB.CC planting is carried out immediately after the previously cultivated plants are harvested or after soil processing.The planting distance for cowpea is 40 x 10 cm.Each planting hole contains 2 cowpea seeds.Furthermore, thinning was carried out at 1 week after planting.

Cover crop maintenance.
Maintenance activities carried out on CC plants include watering using fanfare.It needs watering once a day.And if it rains, it does not need watering.

Post-emergence herbicide application.
The post-emergence herbicides used in this study were herbicides with the active ingredients topramezone and atrazine.The dose of the herbicide applied is the dose according to the recommended label.This pre-emergence herbicide is applied immediately after tillage or clearing of areas, when weeds have 3-5 leaves.Herbicide application is carried out in the morning and the weather conditions are not rainy.

2.3.7.
Pre-grown herbicide application.The pre-emergence herbicide used in this study was a herbicide with the active ingredient pendimethalin.The dose of the herbicide applied is the dose according to the recommended label.This pre-emergence herbicide is applied immediately after tillage or clearing of areas, prior to planting corn.Herbicide application is carried out in the morning and the weather conditions are not rainy.

Cover crop termination.
Termination of CC is done by cutting CC down to the base of the CC stem.This termination is carried out during the early flowering period of CC.After felling, the next important thing is to ensure that the CC is evenly distributed in the plot.Furthermore, CC will be allowed to stand for 2 weeks before conducting soil analysis II and planting corn.
2.3.9.Soil analysis II.Soil analysis I was carried out after the treatment of both weed control techniques (P) and land management techniques (T) was carried out.Samples for this soil analysis were taken as many as 30 plots from the research area with a depth of 0 -20 cm using a hoe and soil drill, then put them in a plastic sample.Parameters to be analyzed included pH H2O, Organic-C, N-total, bulk density, P-available, CEC, total microbes.

Observation parameters.
The physical properties of the soil tested were bulk density.Soil samples taken from each plot were calculated using the following formula: D = M / V, where: D: Bulk density (g/l) M: Weight of the full container (g) V: Container volume (l).The chemical properties of the soil tested were pH H2O, total-N, available-P, CEC.Soil samples taken from each plot were tested for pH H2O using the Electrometry method, total N using the Kjehldahl method, available P using the Bray II method, CEC using the exchange bases test method.The biological properties of the soil tested were Organic-C and total microbes.Soil samples taken from each plot were tested for Organic-C by the Walkley and Black method, and totalmicrobes with Total Plate Count method.

Results and discussion
The results of the pH analysis of the 10 treatments obtained an average value as shown in Figure 1.Based on Figure 1. it shows that the highest average soil pH was in the P4T1 treatment at approximately 5.753 (slightly acidic), while the lowest average soil pH was in the P0T1 treatment, is around 5.450 (acid).In this study, pH did not have a significant effect.However, it could be seen the difference in pH value in each treatment, pH was higher in the weed-free treatment with tillage (P4T1) compared to the treatment without control and tillage (P0T1).This is because weed control by tillage helps reduce residue from planting.Treatment without tillage (NT) will decrease the pH by 0.04 -0.10 in some soil conditions, but treatment with conventional tillage (CT) reduces the pH by 0.01-0.02 in various soil conditions [10].
Phosphorus content was higher in the treatment using pre-emergence with tillage (P2T1) compared to the treatment without weed control and with tillage (P0T1).One of the factors that affect the availability of phosphorus in the soil is soil microorganisms.This is because the substances contained in herbicides do not have a negative or neutral effect on the activity of soil microorganisms [11].The results of the phosphate analysis available by the Bray II method of the 10 treatments obtained the average value as shown in Figure 2. Based on Figure 2. it exhibits the highest average available phosphate content was in the P2T1 treatment around 3.055 ppm, while the lowest average available phosphate content was in the P0T1 treatment at approximately 1.762 ppm.The results of the bulk density (BD) analysis of the 10 treatments obtained an average value as shown in Figure 3. Based on Figure 3, it is known that the highest average soil bulk density value was in the P1T1 treatment around 1.266 g/cm 3 , while the lowest average soil bulk density value was in the P2T1 treatment at approximately 1.0 g/cm 3 .In Figure 4, it shows that T0 (without tillage) tends to show stable results in each weed control treatment (P0-P4).However, T1 (with tillage) showed differences between weed control treatments (P0-P4).On the other hand, tillage treatment and weed control did not significantly affect Bulk density, but it can be seen that without tillage (T0) the Bulk density values tend to be stable compared to tillage (T1).This is because there are no disturbances such as compaction and stretching of the pore space in the soil [12].
Based on the data on soil BD, the results show the correlation between BD and organic-C, which is in the T0 (without tillage) treatment, the stable data of BD makes the organic-C higher than in T1 (with tillage).This is because accumulation of soil organic C (SOC) with time may reduce the soil's susceptibility to compaction.T1 (with tillage) management-induced increase in SOC improves the soil's ability to resist compaction [13].The results of soil organic carbon analysis of the 10 treatments obtained the average value as shown in Figure 5. Based on Figure 5. it shows that the highest soil organic-C content was found in the P0T0 treatment around 1.090% while the lowest soil organic-C content was in the P3T1 treatment at 0.803%.Soil organic C content was higher in the treatment without weed control and without tillage (P0T0).This happens because the soil organic matter which is generally found on the surface of the soil does not get tillage or weed control.Therefore, the soil surface remains closed and there is no carbon that evaporates due to soil turning and weed control on it [14].
The results of the total microbial analysis of the 10 treatments obtained an average value as shown in Figure 6.Based on Figure 6, it is known that the highest average total microbial content was found in the P0T1 treatment at approximately 48, while the lowest average total microbial content was in the P1T1 treatment at 10.However, excessive use of herbicides and for a long time affects the population of microorganisms.This study found that the treatment without weed control and tillage (P0T1) had a higher population of soil microorganisms.This is influenced by the content of herbicides which are toxic and affect the stability of biochemistry in the soil [11].
The results of the analysis of N-Total soil from the 10 treatments obtained the average value as shown in Figure 7. Based on Figure 7, the highest soil total N content was in the P1T1 treatment at around 0.130%, while the lowest average available phosphate content was in the P0T1, P3T1, P4T0 treatments at approximately 0.090%.The total N-content in the soil is affected by the presence of legumes as cover crops (CC).It is known that the P1T1 treatment showed higher yields, where P1 was a weed control technique using cover crop (CC).This is because legume plants have root nodules which are the result of a symbiosis between rhizobium and leguminous plants.Rhizobium can absorb free nitrogen from the environment and convert it into a form that can be utilized by plants.This process is known as nitrogen fixation [7].
The results of the soil CEC analysis of the 10 treatments obtained the average value as shown in Figure 8.Based on Figure 8, it is known that the highest soil CEC was in the P1T1 and P2T1 treatments around 22.333 while the lowest average soil CEC was in the P1T0 treatment at approximately 15.333.One of the affects the CEC value is Organic-C.In this study, it was found that the treatment of weed control techniques using cover crop (CC) with tillage (P1T1) affected soil CEC but not significantly.This is caused by tillage only reducing soil porosity but does not affect the organic matter content in the soil [15].

Conclusions and suggestions
The weed control technique is the use of cover crop (CC) (P1), it only affects the nitrogen value in the soil due to the presence of root nodules.While the tillage technique (T0) affects the bulk density (BD) which tends to be stable and the Organic-C content is quite restrained due to no evaporation due to tillage.The use of cover crop (CC) and no-tillage can be an alternative to maintain soil quality.

Figure 1 .
Figure 1.The average value of soil pH.

Figure 2 .
Figure 2. The average value of soil available phosphate.

Figure 3 .
Figure 3.The average value of soil bulk density.

Figure 6 .
Figure 6.The average value of total microbes in soil.

Figure 7 .
Figure 7.The average value of soil total nitrogen.

Figure 8 .
Figure 8.The average value of soil CEC.
Systems 27 pp 68-80 [10] Zhao X, He C, Liu WS, Liu WX, Liu QY, Bai W, Li LJ, Lal R and Zhang HL 2022 Responses of soil pH to no-till and the factors affecting it: A global meta-analysis Global Change Biology 28 pp 154-66 [11] Riah W, Laval K, Laroche-Ajzenberg E, Mougin C, Latour X, Trinsoutrot-Gattin I 2014 Effects of pesticides on soil enzymes: a review Environmental chemistry letters 12 pp 257-73 [12] Jabro JD, Stevens WB, Iversen WM, Sainju UM, Allen BL 2021 Soil cone index and bulk of a sandy loam under no-till and conventional tillage in a corn-soybean rotation.Soil and Tillage Research 206 p104842 [13] Blanco-Canqui H, Stone LR, Schlegel AJ, Lyon DJ, Vigil MF, Mikha MM, Rice CW 2009 No-till induced increase in organic carbon reduces maximum bulk density of soils Soil Science Society of America Journal 73 pp 1871-9.[14] McBride SG, Osburn ED, Lucas JM, Simpson JS, Brown T, Barrett JE, Strickland MS 2022 Volatile and Dissolved Organic Carbon Sources Have Distinct Effects on Microbial Activity, Nitrogen Content, and Bacterial Communities in Soil Microbial Ecology pp.1-10.[15] Gao L, Becker E, Liang G, Houssou AA, Wu H, Wu X, Cai D, Degré A 2017 Effect of different tillage systems on aggregate structure and inner distribution of organic carbon Geoderma 288 pp 97-104. 9